Apparently the answer to “…the question of what it would take for people to notice climate changing, since they only directly experience the weather…” depends on your ideological bent, at least in the USA. There is a nice piece on Ars Technica about the paper.
Yes, values will become apparent when those non-linear effects start kicking like a mule. Like the 1 degree higher effect on corn growth, when the corn suddenly dies. GW is apparent when you see it on your plate.
I may have mentioned it earlier, but it is also worth noting that a lot of infrastructure, buildings and installations have been designed and dimensioned based on the climate in Hansens baseline period.
Building codes are typically based on 100-year events, or some analog improbability, for the local climate. During Hansens baseline period building codes were changed from rough overestimates to scientifically optimized requirements, in order to make buildings cheaper to build.
Analog observations can be made for how power transmission, drainage, bridges have been constructed in the last 50 years.
Five sigma can become very expensive for insurance companies.
Comment by Poul-Henning Kamp — 19 Aug 2012 @ 4:28 AM
Hansen’s analysis and its implications seem clear for anyone used to thinking about probability distributions. It’s also clear that extreme weather events cause disproportionate damage to human and ecological systems. The probability distributions published by Hansen are a logical extention of his “loaded dice” analogy.
It is very helpful to get an clear commentary from an informed scientist like you on this paper. Thank you for all your contributions.
Is this line correct:
“the causation is for the metric “a monthly anomaly greater than 3 sigma above the mean”.”?
I thought that the anomaly that Hansen calculates is the anomaly for the three month JJA period, not for single months. This is relevant in Hansen’s analysis of the 1930′s droughts, where July and August were extreme but the three month anomaly was not three sigma off the reference period. Extreme weather like this year’s “summer in March” also do not show up in Hansen’s analysis, since it was only about a month long. Rahmstorf and Coumou’s result addresses these short term records while Hansen addresses longer term change.
Keep up your great work, your work raises the web conversation on other blogs.
[Response: Thanks. You are correct – it should be the seasonal change. – gavin]
You discuss the change in extremes by increasing the temperature 1C. Is there any reason to assume (as Hoerling and Mass do) that a 1C average increase in temperature would result in a 1C increase in extremes? It is well known that drought contributes to heat waves. If March, April and May were 1C warmer and evaporated a lot of water, wouldn’t that make it easier to have a 3C anomaly in summer since the ground is preconditioned for heat? Thus much more than 1C of the extreme heat could be due to global warming because of this local effect. There is data to show warming is greater in winter than summer. There is no a priori reason to suppose that a 1C increase in the annual temperature would lead to a 1C increase in extremes, the extremes might be greater or lesser. Hoerling and Mass have presented no reason to suppose that their basic premise is correct.
[Response: Indeed. I think there are certainly going to be non-linearities at the extremes – associated with soil moisture, fire, smog etc. – depending on where you are – and that makes the linear addition attribution metric even less satisfactory. But these issues are hard to quantify – both from the observations (since there are few occurrences) and models (which might not be complete/detailed enough to include these effects). – gavin]
Wouldn’t it make sense to parameterise the mean and the width of the gaussian distribution as a relatively smooth function of time (just a polynomial?), and then do an unbinned likelihood fit? That way you’d automatically take care of the effect of putting your data in bins of 10 years.
And then you could plot the resulting fitted functions versus time.
I’m genuinely curious if the gaussian is also getting wider, not just slowly shifting up.
Sorry for being a bit data-technical, and it would remain a bit of the problem to have nice convincing plots with data .. but doing an unbinned analysis does make sense, doesn’t it?
I recommend reading the “First Four Years” by Laura Ingalls Wilder. It was published posthumously in 1971 and might or might not be part of the Little House on the Prairie series (which was published in the 30′s and 40′s). In any event if you want to get a feeling for the effects of extreme weather it is a good one.
The incident from the book that I am thinking of is the following. Each year something happened to destroy their crops. One year everything was going perfect. They were finally going have a great harvest and pay off all their debt. Then, just before harvest time, a hot dry wind blew for three days and destroys their crops. If the change in wind had been averaged over the summer instead of occurring all in three days there’d have been no effect.
The Wilder book, “The Long Winter,” is another incredible portrayal of how weather effects life on the great plains.
Comment by John E. Pearson — 19 Aug 2012 @ 9:28 AM
You say the affects of a heat wave are very non-linear.
I can’t agree more. I work outside all summer. Sometimes doing work which requires wearing heavy clothing and carrying a lot of gear. I also exercise outside early in the morning when the daily temp is at it’s minimum. And I do this in Texas. The difference between 74f vs 77f, our climatological normal and what we’ve experienced these last two summers, is an incredible amount of distress.
Not everyone in the world runs from their house to the car to the office and can escape the increasing heat. When I think of the projections that show a 2C or 3.5F increase in average global temps in my lifetime it makes me feel hopeless. This will translate to 5 or 6 degrees F temperature increase experienced during my summer morning routine (expected increase in NH continental, summer, minimum temp) compared to the climatological norms my now retired coworkers used to deal with. I feel sorry for the poor folks next in line (my two kids).
Just curious, as the Thirties are held up by some as a natural time of heat events, what would Dr. Hansen’s method look like if the baseline was from 1921 to 1950? Would this in any way be able to tease out the natural from the anthropogenic?
[Response: While warm in the US, the 30s overall were not that warm, and so the percentage of 3 sigma + events globally was lower than the last decade. Hansen’s post-publication discussion has the data for 30s with respect to the 1951-1980 baseline, and the difference seen in using a 1931-1980 baseline (not much). – gavin]
An interesting analysis, but I can’t agree. Expressing climate change in terms of sigmas, and particularly exceedance of three sigmas, is less useful than other approaches, and potentially highly deceptive. In communicating with society and dealing with impacts, it is far more valuable to stay in true physical space. People understand temperature, not sigmas. The impacts are based on temperature and most official web sites, such as CPC, provide anomalies in C. Water freezes when temperature drops to 0C, pine beetles live if temperatures exceed a certain threshold. People can understand when you tell them 1 C of an anomaly is cased by global warming—it has meaning.
Using sigmas, and particularly a threshold of sigma, is quite deceiving. And examining a percent exceedance is worse. The truth is that many locations that exceeded 3 sigmas, would have been 2.8 sigma (or something like that!) without global warming–but no one says that. Hardly something that 99% of the folks would understand. Furthermore, 3 sigmas is entirely arbitrary and without physical meaning…unlike true temperature. But most serious of all, because of the highly non-linear shape of the gaussian, a relatively modest shift in temperature can cause a BIG change in percentage exceeding a threshold. A good way to scare people, but not a good way to communicate information. The implication given by many is that places that are exceeding 3 sigmas would have been normal without GW—this is simply not true.
Finally, the non-linearities in the impacts due to GW is an interesting issue, but it is not our place to juice our indices to be highly non-linear because we suspect such non-linearities exist. We need to give people the straight story….one they can understand…and that really needs to be in terms of physical temperature anomalies. …cliff
[Response: Before I get to the substance of your comment, I have to say that the use of terms like ‘deception’, ‘deceptive’, ‘deceiving’ and ‘juicing’, really are not appropriate for a scientific discussion. I think we can all agree that climate is complex, and there are multiple facets that can be communicated, but to say that someone who communicates a different view of the situation is deliberately out to deceive people is unfortunate at best, and offensive at worst. Given that there are people who regularly falsely accuse climate scientists of misconduct, fraud and deception for doing nothing more than reporting the facts, your use of these terms is inappropriate and not conducive to an improved public discourse.
Your first point seems to be that the public can’t deal with the concept of a distribution and so we shouldn’t talk about sigma’s because some people won’t understand. This is frankly bizarre. The public consist of many individuals who vary enormously in the attention they pay this discussion and in their background level of knowledge of statistics. Because someone might exist for whom this conversation is beyond them is no reason not to have it. But I even don’t agree with your basic assumption, most of the public have an intuitive grasp of distributions – look at the interest in playing poker, backgammon or craps. Statistical arguments given in terms that people can relate to, like dice throwing, are actually quite easily communicated.
Your second point is that absolute temperatures are more ‘real’ than sigmas, or presumably anomalies. I don’t really disagree, but it clearly isn’t the case the impact of 100ºF is the same everywhere – that is cool for a Phoenix summer day but almost unbelievable in Maine. Since climate is related to expectations – which differ enormously from place to place – anomalies allow you to look at similar levels of impacts and spatial coherence of the changes much more clearly. But obviously, anomalies aren’t ‘real’ in the sense you describe either, but are still very useful for scientists and lay people alike. Finally, dealing with distributions and deciles and sigmas is not that much of a leap – people understand the concepts of signal and noise with respect to the stock market, or tuning a radio and can grasp the idea with respect to climate and weather and extremes as well. There is nothing ‘deceitful’ in abstraction.
Your point about ice melting at 0ºC or temperature constraints on pine bark beetles actually reinforce my point and contradicts your second-to-last paragraph. Both of these effects are threshold events where any warming below the threshold is basically irrelevant, but the warming that crosses the threshold is responsible for all of the change. These are then classic cases where return time analysis and extremal exceedance are precisely the metrics that would be most tightly coupled to impacts. 3 sigma is of course arbitrary, but the same features are seen whatever threshold you pick, so that is hardly salient.
It might be obvious to you that shifts in the mean give rise to proportionately much greater numbers of warm extremes, but this isn’t necessarily true for anyone else. I don’t see how pointing this out, and showing that it is really occurring is ‘scaring’ people. Why is this fact something that should not be communicated? [For a very real example of the increasing impacts of small changes on the extremes, check out the graphs of Acqua Alta in Venice…]. And who has said that no heat waves would occur without GW? Or no El Niños or La Niñas? Not Hansen, Allen, Pall or Rahmstorf. If your beef is with distortions in the media or on headlines, then direct your criticisms to that, not to the scientists. – gavin]
[Response:I fully agree with Gavin, but here is an added simple point: if you prefer a temperature value rather than sigma, you could do the same analysis using the global mean of the sigma value (which is 0.6 degrees celsius). I.e., instead of plotting how often 3-sigma anomalies occur, you could plot how often anomalies exceeding 1.8 degrees occur. You’d get almost the same result as Hansen et al. Doing it that way would just be less sophisticated and informative, because in some places 1.8 degrees would just by nature of the local natural variability be exceeded much more easily than in some other places, so using that kind of threshold would not be as “fair” and even-handed as the 3-sigma threshold. -stefan]
It is so refreshing to read a logical, well reasoned interpretation of a paper without the hype and mis-interpretation [purposeful?] of the data and intent.
The Op-Ed in the WSJournal recently, is as bad an example of a comment I can imagine, that contributes nothing to a better understanding of this issue of climate change.
Thanks. Could you comment on the following in regards to whether Hansen’s type of analysis is relevant to daily extreme’s as well seasonal?
From Dr. Jeff Masters blog on the 15th of Aug the following data was provided.
Aug 13, 2012 Needles, CA, temp 118 F it started raining – a world record for hottest temp and rain
Jun 5, 2012 Mecca, SA, temp 109 F, rain, previous world record
July 10, 2010 Marrakech, Morocco, temp 109 F, rain, previous world record
Having world record daily weather events, such as the above, occur in such rapid sequence would seem to imply that Hansen’s type of analysis could be applied to daily events as well. The deviation between Jun 5 and Aug 13 (9 F) would seem to be very large. Is his research relevant or someone else’s?
Could you comment on the this. Thanks.
[Response: Hansen’s analysis was for seasonal anomalies – which are still averaging over a lot of weather. The shorter the time frame, and the more specific the extreme, the harder it is to detect a change, let alone attribute it. The most successful attempts to do this have used either global or continental statistics (as above), or thousands of model simulations of a local event (which use an initial condition ensemble to provide statistical power). It is certainly not the case that there is demonstrable link between every extreme and climate change (and indeed, some extremes – like bitter cold spells – are predicted to become less frequent). Looking at daily records can be insightful, but only when you have enough examples and a good metric to be comparing – the straight number of warm records is not good because even in a static climate you expect structure, but the ratio of warm to cool records is quite good because the expectation is that it should be 50:50 in the medium term (Meehl et al, 2010). Since the beginning of 2010, they are running ~4:1 in the continental US – though I am not sure about the rest of the world. – gavin]
Looking at specifics, Extremely Hot Summers (defined as a +3-sigma seasonal anomaly) increased from 0.1~0.2% of area in 1951-1981 base period to about 10% last decade (2001-2011). This is a factor of 50X~100x, or 5000% to 10,000% increase in 50 years. So now when a +3-sigma event happens, we know that the probability it was due to natural variation is 1/100 to 1/50 (1% to 2%) and the probability that it was due to global warming is 98~99%. That is for a single event. The probability that a string of such events are all due to natural variation is, as Dr. Hansen says, “minuscule, vanishingly small”.
In terms of return times, the Extremely Hot Summers used to occur every 500~1000 years at a particular location during the base period and they occurred about every 10 years during the last decade (and it is extremely likely that it will be more often this decade).
If this all wasn’t scary enough, +4-sigma events are now happening about 5% of the time and +5-sigma events, that formerly had a return time of about a million years , are now occurring about as often as 3-sigma events happened 50 years ago. With further warming, +4 and +5-sigma events will become “normal”.
“but it is not our place to juice our indices to be highly non-linear because we suspect such non-linearities exist. We need to give people the straight story…”
In my comment #10 I point out that non-linearities can go both ways. Your suggestion that I discussed only raising temperatures is a deliberate deception. We know nonlinear effects exist but we do not know whether they make the temperature higher or lower. In your blog commentaries you claim absolute attribution and do not mention these uncertainties in your analysis. It is you who are deceiving your readers since you conceal your uncertainty. It is well known that hot weather breeds more hot weather. Please provide evidence to support your wild claims that the expected temperature increase in heat waves would be the same as the annual temperature increase.
You have made a large number of insulting comments accusing other scientists of deceiving readers without providing any specific examples or allowing comments to the contrary on your blog. You need to provide specific examples or stop insulting others. It appears to me that you are wrong and Hanson is right. If you think your argument has merit write up a paper and see if anyone will publish it. What you have put in your blog will never see publication, it has too many obvious errors.
Considering that Cliff rather insultingly dismissed authors of other remarks on his critique as ill-equipped to discuss this topic, I must say I find Cliff’s remarks here remarkably undistinguished in terms of revealing any special capabilities for illumination. Strictly garden-variety personal opinion.
(5 sigmas are so rare that putting them within such a variable background as climate that it seems to me to be meaningless.)
But weather events aren’t a once a year event so I have a hard time understanding the denominator
[Response: Hansen et al. look at seasonal anomalies, especially those for the average temperature of June-July-August. This anomaly can be computed (at each point of the globe) exactly one time for each year. An event of this type with a 1/100 probability thus would be expected to occur once in a hundred years. -stefan]
Hansen is a great scientist, but group psychology is not his field.
Consider the 2010 Russia heat wave/ Pakistan flood. They were 3-sigma events, however NOAA promptly wrote an “attribution” calling the heat wave natural variation, and ignoring the related Pakistan flood.
And that was the professional weather community. Mostly, Americans ignored the event.
People will not take dramatic action on climate change until it bites them on their ass (e., g., a catastrophic, 9-sigma event). And, by then it may well be too late.
This summer we are seeing the 6th consecutive major Arctic sea ice melt event, and it has not even been mentioned in the presidential campaign. They have not tied this summer’s drought to AGW. They have not tied last winter’s South American drought to AGW. So look up and see what RC was saying, or equivocating and not saying about Arctic sea ice loss last April. What does RC say about five consecutive 4-sigma melt events in the same region?
As a certified “Alarmist” I must predict that we will see a substantially sea ice free Arctic — next summer. Will that prompt real action against AGW? Not unless it changes NH atmospheric circulation and we have another drought year, the crops fail, and the price of food goes up — a lot.
There are many ways to convince oneself that one is right. Most of them are not scientific in nature.
I have found that of those that do not understand climate science well, extraordinarily few have the needed expertise regarding the relevant scope of the field… Even when they themselves are professors or scientists.
Sophist argumentation based in a distinct lack of knowledge is not a foundation upon which anyone, especially scientists or professors should base their arguments upon.
The Dunning/Kruger Effect illustrated by Isaac Asimov as a false premise:
“My ignorance is just as good as your knowledge”
It seems some still think this is a good argument and that argumentum ad ignorantiam should hold an equal place in any debate?
Though those of a thoughtful nature may still shake their heads and wonder why…
Re- Gavin in his inline response in Comment by Clifford Mass — 19 Aug 2012 @ 10:37 AM:
I would like to add to your comment about the varying ability of the general public to understand climate science, that I also think that an even more important function is communication between scientists. A complicated problem is often dissected and studied in many different ways that are mostly understandable only by experts in the area. This is how most sciences proceed and to try to do teaching to the general public within research papers would require special sections in the journal, and external support for excess page charges and free public access to the journal articles.
It is easy to argue that the most important function of climate science to the general public is education for political purposes and I agree with this, but the best way to do this is to get the most accurate information from the scientists. Those who wish to spin scientific findings to favor their political or economic viewpoint do quite well twisting even the most straightforward data (e.g. surface temperature stations). Disseminating science to the public is a different specialty. Steve
It also depends on how you define extreme. Hot weather extremes may be more prevalent in some locations, but cold weather extremes which can be more injurious to agricultural interests seem to be decreasing. I was looking back at some historical Climatological Data reports for Ohio from the NCDC archives and you can certainly see the effects of climate change. Light frosts were reported to have occurred in July in many of the early years, with even a locally damaging frost in a couple of those years in outlying areas. This just simply doesn’t occur anymore. Frosts are very rare now even in June & August, when they used to be fairly common in the 19th Century.
Clifford Mass not only insults scientists as Gavin points out, but insults “society” by claiming we non-scientists must be spoon-fed the real world in simplistic terms that actually paint very fuzzy pictures, exactly as his blog post does – a bunch of hand waving that explains nothing while claiming to counter a reasoned and clear exposition of the true state of the climate. The paper in question and Gavins elaboration of it are waaay easier to follow and understand for this “average” layman.
Gavin in comment to to #18: “The shorter the time frame, and the more specific the extreme, the harder it is to detect a change, let alone attribute it.”
Yet that is exactly what the JASONs did back in 1992.
Their point was that the rate of new extreme values can be attributed and therefore their conclusion amounts to “Seing N new records…” (rather than “Seing this new record”) has odds of 1:1e5-1e6 of being climate change.
Extreme values (= weather records) are the inverse canary in the climate coal-mine: The more you see of them, the worse it is.
Comment by Poul-Henning Kamp — 19 Aug 2012 @ 3:53 PM
Re: Drought and high temp
Mueller and Seneviratne in PNAS address correlation between lo precip and subsequent hi T
The absence of such contributes to many social ills, whether failing to understand how health risks should be borne by a broad support to help curtail individual risk, the purpose of insurance, performance of social systems, or how reducing individual costs by allowing coastal construction in flood zones is based upon a lottery mindset. People think they can “get away with it”. Maybe that’s human, but it is also foolish. Jan
“Scientists have long warned of more frequent floods and droughts as the world’s climate changes. But for Mr Mainord and many like him, global warming is bogus. “It’s more God and nature’s dictates, rather than a man-made event,” the Missouri farmer said this week as he harvested a corn crop one-quarter of its normal size.”
Scientists have long warned of more frequent floods and droughts as the world’s climate changes. But for Mr Mainord and many like him, global warming is bogus. “It’s more God and nature’s dictates, rather than a man-made event,” the Missouri farmer said this week as he harvested a corn crop one-quarter of its normal size.
Good presentation for scientists, of which the majority agree with AGW. Clifford Mass disagreement is incoherent, not at all in line with reality, he has to make a case when significant sigmas show warming when there is actually GT cooling, actually I am sure that there are contrarians out there who believe in the looming coming ice age, but strictly looking at data from the Arctic, there is a great warming happening. I am not sure if WUWT fans know that here are no urban heat islands over the arctic ocean?? However most people know what is going on. Mr Mass presumably included. There is a lot more heat showing in all seasons especially in the Northern Hemisphere exactly where it should happen. So the claim for dishonesty is rather a political ploy, a practice that they usually do, of course, practicing incorrect interpretations always gives no respectable prediction results, which by miracle from chance, if they would do one would be quantified as a high sigma anomaly not respecting any trends.
Comment by David B. Benson — 19 Aug 2012 @ 5:57 PM
Hi Gavin, Great article. Very enlightening for someone with a Maths background and increasing understanding of climate change. I was interested in Chris Mass comment at #16. I would agree with him only in suggesting that most of the public have no clue about statistics of this level. Most people do not study Maths beyond standard deviation and mean, and rarely understand even that, so forget it very quickly after leaving school. So they would have no chance of following this article.
16 Clifford Mass wrote: “People can understand when you tell them 1 C of an anomaly is cased by global warming—it has meaning.”
I to only has meaning if you’ve done the analysis correctly and that is impossible to tell from your comment.
For the sake of discussion (FTSOD), assume we’ve had 1.5C change in mean temperature. Consider heat waves of some given magnitude, say 7.5C which FTSOD are once per century events without global warming and once per decade events with global warming. If I’ve understood you correctly you want to tell the people that the mean temperature increased by 1.5C and that it follows that 1.5C of the 7.5C heat wave is due to global warming and the rest is “natural”. It would be a reasonable to tell the people this only if there were 6C (7.5C-1.5C) heat waves every decade during the climatological period. This shouldn’t be difficult to check. Have you checked to see if your claim is correct? If you have I’d very much like to read it.
Comment by John E. Pearson — 19 Aug 2012 @ 9:18 PM
First, the definition of deceptive is:
“Giving an appearance or impression different from the true one”
Please don’t take the word further than I meant it. If you would prefer confusing, that is fine with me. You talk about using politic language as scientists…and then in the next paragraph you call my conclusions “bizarre.” I haven’t seen that word in many papers.
Regarding whether folks understand three sigmas, I give a lot of public talks and last week I asked a ground of roughly 150 highly educated folks how many understood what that meant—6 raised their hands. You can reach your own conclusions on this. I commend those laypersons comfortable with such stats…but most of the population and media don’t have a clue what it means.
You talk about anomalies being important…I agree…give them in degrees rather than sigmas to the general community if you want it understood.
And regarding transitions (like freezing)…there is no reason they would align on three sigmas or any other such basis. As noted in my original email, arbitrary lines in the sand like three sigma are inherent confusing and problematic. And the percentiles exceeding such 3 sigma thresholds increase rapidly with even moderate anomalies.
Folks…I know I am entering the lion’s den talking in this forum, but Hansen had no basis to say confidently that last summer’s heat wave was caused by global warming. …cliff
39 wayne davidson wrote “Clifford Mass disagreement is incoherent,”
I don’t agree that it is incoherent. Well, actually I re-read it and it isn’t exactly coherent, a bit of a rant I’d say, but he does have a legitimate point but it has to be checked. If global warming gave us dT of warming and we see extreme events with temperature dT_ext Clifford Mass claims that it is fair to say that of the extreme events dT is attributable to global warming and the rest is “natural”. This is a quantifiable claim. It isn’t a matter of opinion. If the frequency of dT_ext-dT events is the same before global warming as dT_ext events are after warming then Clifford is correct. If the frequency of dT_ext-dT events during the climatological period is much lower than the frequency of dT_ext events during the warm period then Clifford is incorrect.
Comment by John E. Pearson — 19 Aug 2012 @ 9:41 PM
” it is far more valuable to stay in true physical space. People understand temperature, not sigmas.”
Cliff, you managed to string a grand pair there! Made almost sorta reading your comment worthwhile.
The OP is about expectations and effects in the real world as it affects real people in local areas. If you want to know what a warmer world might be like for your town (ie, without surprises) then look to a period where that happened, as in the USA this year. Winter was grand, so the bugs didn’t die. Mosquitoes threatened. Fortunately, the rains failed and the skeeters died off. But the crops did too. And golly, the length of the hot events seemed longer than usual, and more than 2 degrees hotter, too…
It’s just anecdotal, but it’s probably pretty median. Of course, that’s just for an average year. Look at Hansen’s graphs and figure how wide the curve would be with the median at 3 sigma or so, and re-scale so the median is 0 sigma. Now visualize a 3 sigma event… better hope variability doesn’t keep increasing…
John Pearson @13 The incident from the Laura Ingalls Wilder book about hot, dry winds killing crops in an (until then) good year in the 1930s was probably based on an actual occurrence. Just such an incident was related to me by my father-in-law, who farmed in northeast Nebraska in the 1930s. He mentioned that he thought the crop finally looked good in 1937, until a hot, windy day killed the corn outright. I saw a confirming notation of dead corn in an observation log book kept by the Weather Bureau in Norfolk, Nebraska for August 15, 1937. They recorded a high of 106 with a strong southwest wind. Wind from this direction usually has very low humidity on the Great Plains.
So this is not just temperature, it is a multitude of factors which affect the damage output. Another example would be ozone levels which become more unhealthy with high temperatures or the heat index.
Never mind the heat – feel the humidity
A look at the combined effect of heat and humidity
At the time of writing, the early morning temperature in Doha was 37C – not too bad you might think. But the relative humidity was 60%. The combination of the two gives a heat index of 51C – definitely unpleasant conditions.
Now to contribute a single event to Global Warming, one has to look at the weather conditions, and if patterns are sighted which are tied to alteration of sea ice decline (our new atmosphere set up), we can connect the dots here too.
You are not entering the lions’ den, but are rather participating in a world of very bright scientists. Your claim that Hansen failed to establish a link between hot summers and global warming- something he established through temperature readings and detailed statistical variance analysis- is false.
Sorry, Cliff, we don’t have time for chumps here, especially the verbose kind, who have just enough knowledge to get in a lot of trouble.
Sigmas: Most people THINK they understand statistics. But Prob& Stat class was a real shock. I came out a different person.
Comment by Edward Greisch — 20 Aug 2012 @ 12:00 AM
#44 cliff mass
I will agree with you that most don’t really understand ’3 sigma’. I know I’m not a math or statistics expert.
But is a science paper the best place to ‘not’ use scientific language, or maybe it’s okay in science papers to be scientific and then to have folks such as yourself, talking to a non scientific audience, explain what it means using relatable percentages, such as the ‘roll of the dice’ analogy (which really isn’t that bad because it is relatable).
re. “Hansen had no basis to say confidently that last summer’s heat wave was caused by global warming”
This is where I get confused.
Are you saying that loading the climate system with 29 ZJ (increased RF) of energy every year or that the cumulative effects of increasing the loading over time, say more than a century, would not increase the odds of having heat waves?
Are you saying that all heat waves that are occurring right now are not occurring in a system loaded with said extra energy?
If so, upon what scientific basis? And if per chance your going to bring up the ‘Iris Hypothesis’ I would remind you that it has not been indicated as having significance in the available data and there are many reasons to doubt the strength of said self regulating mechanism such as: data indicates it ‘has’ been warmer in the past.
So upon what confidence do you base such a ‘claim’ that the enhanced greenhouse effect is not influencing heat waves right now?
Let me put it this way. Let’s say you are in a car, in the back seat, and the driver is heading south down highway 5. Are you saying it’s okay for you to claim without evidence that since you are not in agreement that the car is heading south on highway 5, such a fact/observation is specious? You might think the car is headed east, but thinking such does not make it so.
It’s true you are entitled to your own opinion, but you are not entitled to your own facts no matter how many times you tap your heals and wish the increased radiative forcing is not influencing heat waves.
The null hypothesis has been reversed. Can you prove that current extremes in heat waves are not human influenced?
That is something I would like to see. There’s a reasonably old saying don’t try to remove the splinter from your brothers eye until you remove the log from your own.
The gauntlet has been laid at your feet and you asked for it. Prove your point. It’s the ‘Chicago Way’. If Hansen makes a claim and you can show it is wrong, do it. But do it though scientific comment and the relevant peer review, not an email to Anthony Watts. It doesn’t make you look as good as you might think, even though you do get a lot of folks over there fawning over you. Whether you realize it or not, over there, you are fanning the flames of ignorance.
The concept of sigma as it relates to a bell curve is not a difficult concept. The name assigned (“sigma”) may be outside of normal everyday conversation, but the concept is not. If we hold our discourse to only what others can already understand, how will anyone learn anything? Humans can only make intelligent decisions about new phenomena by learning more about them.
You state: “Hansen had no basis to say confidently that last summer’s heat wave was caused by global warming…” Well, Hansen didn’t actually say that – he was much more specific about to what heat wave he was referring. And he put forward a very good argument for his statement, supported by some relatively simple, understandable math. Your statement above, on the other hand, has no such support. That type of logic is the kind of support that is required if you wish to be taken seriously in the lion’s den.
I live in central Texas. Last year’s heat wave was exceptional – and the drought associated with it is really not over. The entire state is having to reassess its water resources, and those numbers are all down. In some areas of the Texas Hill Country that I drove through yesterday, over 50% of the trees are dead. It is very real to us, and, believe me, people are paying very close attention.
You need to keep in mind that Hansen’s paper was published in PNAS. He used sigmas for a scientific audience. Hansen has publicly used the dice analogy to assist people to understand the concept. Here is a non-technical discussion of what sigmas mean.
You have not provided any data to support your wild claim that the annual average temperature change has a relationship to the temperature change in extreme events.
Hansen’s work is peer reviewed. Your work has been widely panned by scientists. Why should I listen to your unsupported opinions?
You still do not mention your uncertainty when you discuss this subject, which is deceptive.
Dutch climatologists Van Oldenborgh & De Laat who were recently quoted in a local newspaper (Volkskrant, August 11) saying:
A) that Hansen is too easily assuming that temperatures are distributed in a Bell curve.
B) that the climatological period 1951-1980 saw exceptionally few heatwaves.
It is suggested that these critiques have significant effects on the paper’ outcome.
Can anyone comment?
[Response: The first is neither are true nor material. The incidence of 3 sigma + events in any one decade is independent of what might be the best fit to the distribution and the Gaussian approximation doesn’t come into any of the calculations above. The second is the basic result – but it is only a relative statement. The number of heat waves (as defined above) was only slightly higher in earlier decades, but has become significantly much higher recently. – gavin]
Prof. Mass – if you’re still participating. I can’t agree with your assessment that your proposed approach is the best way to communicate this type of information. You cite your personal experience in giving talks to lay audiences. I’m a physician-scientist with an active clinical practice. Issues of shifting probability distributions – disease risk factors, differential effects of competing treatments, natural history of disease – are common features of clinical practice. While I don’t use the term sigma in my practice (except when seeing engineers as patients and they usually raise the term), many, many patients have little difficulty in grasping verbal analogues of the type of analysis presented in the Hansen paper. Now, it may be that patients concentrate harder when the questions involved relate to their health than when attending talks on climate science but the Hansen-type approach is, in my experience, readily grasped by individuals from a variety of educational backgrounds.
“Folks…I know I am entering the lion’s den talking in this forum, but Hansen had no basis to say confidently that last summer’s heat wave was caused by global warming. …cliff”
Right! The entire NH warms and there is no basis for Global Warming. Strong compelling nonsense. RC is not a Lion’s den but rather a reality check place, you will not get away with blank meaningless statements here.
A 7 sigma event would occur once in a 1.8 billion years. I can’t find reference to an 8 sigma event. It looks like one in 1.5 trillion. But even a 6 sigma event (1 in 6.5 million years) seems to me to be more exotic than meaningful. Milankovich cycles drastically change climate over a span of ~150,000 years so a 5 sigma event (1 in 58,000 years) is probably as rare as things can get.
As for the Missouri farmer who dismissed AGW and blamed the heat on God, it’s interesting the number of people who don’t know math but who do know the mind of The One who Is.
Heat waves have an origin. They are the superposition of a background field and the effects of the upper atmospheric wave pattern. Generally heat waves, like the ones in the Midwest this year and last, are usually associated with high amplitude and persistent ridging. Now it is clear that GW can increase the background field—but the amplitude so far in the midlatitudes is modest (0 to 2 F perhaps, considering where you are). More in the Arctic. The background does not explain the amplitude Midwest heat waves. But there was clearly high amplitude and persistent ridge during the recent events. Now the question then becomes—is the excessive ridging the last two summers the result of GW? Was the large scale flow pattern somehow enhanced by GW? There is no reason to expect this…either from modeling or theoretical results. So the conclusion we must draw is that these events were mainly from natural variability.
Does anyone know why PNAS editors required Hansen to drop any reference to “climate dice” in the title of this paper?
Hansen has repeatedly drawn attention to the fact that his choice for a title included “climate dice”, e.g.: “the publishers eliminated that phrase from the paper’s title”, and “we were not allowed to keep Climate Dice in the title”.
Ultimately, I think that what Cliff Mass fails to comprehend is that whether one is talking about “global mean” or “sigma”, one is talking summary statistics for a distribution. Merely saying that the mean has shifted by “x” is surely as potentially misleading as looking at the occurrence of 3 “sigma” events.
If Cliff is truly interested in keeping things grounded in “physical reality,” then what matters are the extreme events, as these tend by far to cause the greatest damage. As risk is the product of probability of an event and its consequences, both the probability and the consequences are important.
I do not agree that we must dumb down our discussion to the point where a high school dropout or an MBA could understand it.
I just saw this bit of stefan’s which was added some time later than Gavin’s response to Clifford Mass’s post 16. It’s worth repeating.
[Response:I fully agree with Gavin, but here is an added simple point: if you prefer a temperature value rather than sigma, you could do the same analysis using the global mean of the sigma value (which is 0.6 degrees celsius). I.e., instead of plotting how often 3-sigma anomalies occur, you could plot how often anomalies exceeding 1.8 degrees occur. You'd get almost the same result as Hansen et al. Doing it that way would just be less sophisticated and informative, because in some places 1.8 degrees would just by nature of the local natural variability be exceeded much more easily than in some other places, so using that kind of threshold would not be as "fair" and even-handed as the 3-sigma threshold. -stefan]
Comment by John E. Pearson — 20 Aug 2012 @ 11:23 AM
Gavin’s reply at 58:
“The first is neither are true nor material. The incidence of 3 sigma + events in any one decade is independent of what might be the best fit to the distribution and the Gaussian approximation doesn’t come into any of the calculations above.”
I assume the “are” is a typo, but even without this statement is a bit difficult to parse. Certainly a non-Gaussian distribution will have different probabilities. For 3 sigmas, the best that can be said for a general distribution is that the probability is between 0 and 1/9 (Chebyshev). Even if the distribution is fairly close to Gaussian, I would not be surprised if the probabilities for 4+ sigma events to be considerably larger (“heavy tails”) than Gaussian probabilities.
Comment by Charles Stanton — 20 Aug 2012 @ 11:37 AM
Professor Tony O’Hagan has just published online a summary of a discussion that occurred (raged?) at the International Society for Bayesian Analysis regarding the evidence for the Higgs Boson, and statistical means for demonstrating it. This is a follow-on to the references I posted at #35.
It is interesting that while the Higgs is “new physics”, and demands experimental confirmation, climate change prediction and explication is the application of really well understood physics, by experiment, theory, and in engineering, albeit to complicated systems. To the degree to which sheer system complexity cannot cause conservation of mass and energy to be violated, climate change is inevitable and there is, to me, a strong sense in which Professor Trenberth’s case that if physics is true, that climate change must be so, and that must be here is just being consistent. (I’m paraphrasing and mistakes or distortions are my responsibility.) Hence, the idea of “demonstrating climate change” is a distraction. That’s because the point seriously asks what are we trying to do? Show that climate change’s effects exist contingent upon physics being wrong?
Still I imagine that confirmation of effect, per Hansen, Sato, and Ruedy is a natural exercise, even if what’s available to be measured is an acceleration in the change, not before-and-after.
(@cynicus; Re: #58)
I did recently some statistical experiments with temperature series. I looked at the GISS global temperature data (1880-2011), estimated a quadratic trend (R=0.91), removed the trend from the data and looked for the distributions of the residuals. The distribution is a nearly perfect example for a normal distribution as shown by a quantil-quantil-plot.
Essentially, a 6-sigma (or higher) event means that the statistical baseline was in one system and very rare event means that the system is “out of control”. The system has inherently changed. See the work of Dr. Ed. Deming
This summer’s North American drought is not that rare an event. Last winter’s South American drought was not that rare an event. Now, what are the odds that there will be another drought this year in SA? What are the odds that there will be another drought next year in NA next year?
If we use the baseline data from the 20 th Century, then the odds of droughts in 4 successive agricultural crop seasons is near zero (eg 9 -sigma). However, if the loss of Arctic Sea ice has significantly changed global atmospheric circulation patterns, then we are dealing with a different system that has only been in existence since 2007, and we do not know how often to expect crop failures.
Our agricultural production system is closely linked to the climate as we knew it in the 20 th century (and the 2,000 previous years). It the climate has gone out of control, then the results are likely to be bad for agriculture.
Would somebody here, like to explain to me how we can lose Arctic Sea ice (in part or in whole) without changing the atmospheric circulation patterns? If reduced sea ice is changing circulation patterns, then we may have what a 20 th century weatherman would call a 9-sigma event every year. These are events that did not, and could not, happen in the old weather system.
(In the course of the Milankovich cycles, the system changes, so one would either consider the variance in the system over the entire cycle, in which case the whole cycle is in control and at ~one-sigma; or, one would break system cycle up into shorter segments and look at the variance during those limited periods. If we look at the period from 1,000 to 2,000 CE, the weather was rather stable compared to the last 5 years.)
Both IBM and Motorola insisted that I take Ed’s course on statistics and systems. So, I took it twice and passed it each time. However, my grandfather was a framer from the “Show me”! state
Ladies and Gentlemen, we have a new weather system.
Cliff Mass wrote > Folks…I know I am entering the lion’s den talking in this forum, but Hansen had no basis to say confidently that last summer’s heat wave was caused by global warming. …cliff
He didn’t. You are being deceptive. Let’s actually quote what Hansen et al wrote.
“It is not uncommon for meteorologists to reject global warming as a cause of these extreme events, offering instead a meteorological explanation. For example, it is said that the Moscow heat wave was caused by an extreme atmospheric “blocking” situation, or the Texas heat wave was caused by La Niña ocean temperature patterns. Certainly the locations of extreme anomalies in any given case depend on specific weather patterns. However, blocking patterns and La Niñas have always been common, yet the large areas of extreme warming have come into existence only with large global warming. Today’s extreme anomalies occur as a result of simultaneous contributions of specific weather patterns and global warming.”
You see that detail Cliff? Hansen was talking about extreme events in general, not just last summer’s heat wave, and he clearly states the cause to be both specific weather patterns and global warming. What you wrote gives “an appearance or impression different from the true one.”
This is only a lion’s den if you are here to misrepresent the literature, because here we actually read the primary sources. I’m sure elsewhere on the internet that claim you made is taken at face value as true, when clearly it is not. Details matter.
Comment by Unsettled Scientist — 20 Aug 2012 @ 12:51 PM
Prof. Mass seems disingenuous.
1)Using distributions and sigmas is perfectly valid for a paper in PNAS aimed at an audience of scientists, who presumably are familiar with mathematical language. Are we to understand that all higher math is stripped from papers written by Prof. Mass ? A brief review shows this is not the case. So why does he attack Hansen for doing the same as he does ? If Hansen is to be branded deceptive, what shall we call Prof. Mass ?
2)Hansen makes the case for increasing recurrence frequency of high temperatures in NH JJA. The argument is not about any single hot NH JJA, or the temperature of any particular NH JJA. This is important. Farmers, farming practices, indeed entire societies, have evolved in a climatology where a killing summer heat devastates more than a fraction f of yield every M years. Now the same society is subject to that killing heat destroying fraction f of the crop every M/10 years. The logic is simple, can the farmer or the society thrive or even survive when a heat wave that came one year in fifty year now comes once in five ?
3)From the first graph on this post, it seems that the distribution has broadened, and more to the right (Prof. Rabett has pointed this out before), while moving to the right by 1 sigma. If the shape were unchanged, we would expect that the probability of a n sigma event for the baseline (1951-1980) would be the same as the probability of an (n+1) sigma event for 2001-2011. Not so, the latter is larger, the extreme heat events are coming more frequently than a simple shift in the distribution would calculate. This adds to my concerns raised in point 2) above.
@44 Cliff Mass makes an issue of use of the word “bizarre” in an up-thread Response yet makes light of his own calling folk “deceptive.” Of course, there is a difference between a deceptive word and a deceptive person. But Cliff Mass makes plain he is playing the man not the ball when in his Aug 9 Blog Post he talks of the “…exaggerations of Hansen and his fellow travelers… …it is much worse that that.” “Let me prove to you now that Dr. Hansen’s claims are deceptive.”
And do we see here even in this one Blog Post of his, the dirty old pot calling the shiny electric kettle black? I think we do.
Under a graphic in his Blog Post showing how easily it is for a tenfold increase in “extreme hot weather” to occur, Mass concludes “So the result is that you seem more warm temperature records and less cold temperature records. We are in fact seeing this. The earth is warming and there are more maximum temperature records than cold ones. Hansen and friends make a big deal about this.” (My emphasis.) The word “hot” appears to have slipped form Mass’s vocabulary.
And his concluding assertion does make the attribution of extreme weather a serious issue, not something to dismiss out of hand as Mass appears to want happen. “Lets be clear here. Although the global warming signal is relatively weak today in most of the planet (outside of the Arctic), our best science indicates that the warming will greatly increase by the end of the century.” So if Texas 2011 was attributable to AGW (as Mass asserts it isn’t but with little supporting evidence), this intensity of event will have been relatively weak compared with what we should expect in the coming century.
Cliff Mass has gone into the same argument prior to his Aug 9 piece. On July 29th he discussed climate extremes using the analogy of the 2011 Japanese tsunami to represent natural extreme weather & 10 centimetres of sea level rise to represent the AGW signature. He mentions this because folk are “twisting” the situation so as “…to make the case that global warming is making the weather more extreme. They cite the latest weather/climate disasters as proof: the current heat wave/drought in the Midwest, the Russian Heat Wave of 2010, the Hurricane Katrina in 2005, the list is endless. And headline-thirsty media are happy to amplify this message, to the detriment of their readership. ” (His emphasis.)
“Some organizations, like Climate Central and extremists like Bill McGibben, hype every major weather anomaly as proof of the profound effects of human-induced global warming. ” “They believe by hyping the relatively small impacts during the past few decades that they can motivate people to act. A lie for a good cause.” (My emphasis.) “If you believe in the seriousness of global warming in the future, it is essential to stick to the truth.”
Of course Mass may feel that a linear regression of average Texas summer temperatures since 1895 provides conclusive evidence for his case that AGW is currently far too weak to play a significant role in the Texas 2011 heatwave (an argument he recycles in his Aug 9 blog post), but it is strange Mass picks on Rupp et al 2012 without mentioning Massey et al 2012 in the same collection of papers that similarly finds AGW impacts in excess of Mass’s method (3 times in excess by my calculation).
Cliff Mass presents arguments so utterly foolish that I have elsewhere called him a fool. The more I read of his work on this subject, the more I consider that my statement may have been fully justified.
Actually to understand Cliff Mass’s web site it would help to have had an introductory year on weather or climate. I have had neither, but I like his site on Northwest weather for precisely that reason. It stretches my understanding. He has not addressed the question of how much global warming is locked in at current and likely CO2 emission levels, and oddly attacks people like Gore and Krugman who have accepted common projections.
Ray Ladbury @~64
If we are looking for a layperson’s explanation, available to the untutored like myself, you’ve done it. Thanks.
whether one is talking about “global mean” or “sigma”, one is talking summary statistics for a distribution. Merely saying that the mean has shifted by “x” is surely as potentially misleading as looking at the occurrence of 3 “sigma” events.
… what matters are the extreme events, as these tend by far to cause the greatest damage. As risk is the product of probability of an event and its consequences, both the probability and the consequences are important.
I read Mass’ blog regularly, and when he sticks to Pacific NW weather it’s a great read. I also thought he made some legitimate points about flaws in the Rupp/Mote study, though his presentation was way too acerbic for my tastes.
Which leads to my criticisms: why he resorts to such over-the-top hyperbole re climate change “deception” is beyond me. Especially when he doesn’t (can’t?) back it up.
For instance his comments on this post mainly have to do with presenting the data in a way that the general public will understand. A topic reasonable people can disagree on. But if you read Mass’ blog post and follow-up comments there it’s clear he doesn’t think the Hansen paper is suitable even for other scientists. I.e. it shouldn’t have been published to begin with. Needless to say that’s a very serious criticism of a fellow scientist, requiring a much greater burden of proof than anything he’s presented so far.
I have a naive question about the first figure you use from the Hansen paper. Is there any simple way that doesn’t do violence to the data to plot temperature on the x-axis instead of standard distributions? I’d like to link the Hansen graph to the nice schematic graph that came from the University of Arizona (and they adapted it from the IPCC, I believe). The conceptual graph with temperatures on the x-axis is shown here (http://www.koomey.com/post/29130849206) and here (http://www.southwestclimatechange.org/figures/temperature-shift).
Responding to comments 14, 25, and 56: I’m a policy analyst in Seattle, well-read on the impacts of climate change, but also other global resource constraints–like peak oil, peak phosphorus and the limits of industrial agriculture, waters supply (closely related to climate), and human systems/governance. I have lived and breathed forests, fish, and water issues in the Pacific NW for many years. (Cf. the work of EPA scientist Robert Lackey (Portland OR) on the interactions between population, governance/growth management policies, and salmonids.
For years I have pressed my local governments to consider the very real limits to growth, with little success notwithstanding the clear degradation of the natural habitat and human quality of life in the region. Further, I have had to temper my lobbying with the realization that even if overall population stopped growing tomorrow, many could move from one place to another (America still being a democracy in terms of freedom of movement).
Recently, it has become clear to me that global climate change (warming) is another looming force that will upset advocacy for more effective growth management in the PNW. All projections I’ve seen (e.g., UW CIG) indicate this region will remain pleasantly habitable for people for longer than other areas (think Texas, Oklahoma, Arizona) under the pressure of increasing numbers and extremes of weather “anomalies.” (Western Washington has the lowest annual insolation in the continental U.S.) In other words, we are likely to be the recipient of many climate refugees in coming decades, and we should start preparing for them. Unfortunately, I see that preparation happening about the same time as Aaron Lewis (#25) says we’ll deal with AGW generally—when it bites us in the ass.
Regarding whether those ignorant in statistics can understand Hansen’s latest papers, I’m a perfect test case: My knowledge of stats is low (if I had ever heard the term “sigma” before, I don’t recall it), and only have a basic humanities major’s ability to grasp scientific arguments (well, maybe a little better since I work with scientists as expert witnesses). I would not have raised my hand in the audience Mass asked about knowledge of “sigma.” But that doesn’t mean I don’t get Hansen’s point. I’ll paraphrase what I think he said, and you all who know better can judge whether I “got it right”:
The number of extreme summer heat events has increased (at least in the Northern Hemisphere) in recent decades; they now occur about ten times more often (i.e., increase from c. 1% to c. 10% of the time/area) than during the base period(s) of the early/mid Twentieth Century. Because these events were rare before human GHG emissions forced more energy (heat) into the atmosphere, it is reasonable to conclude that AGW is responsible for (is the cause of) the most extreme events.
Is that close? I did it without rereading the abstract. The temporal and/or spacial extent of the increase is a little unclear to me…
Here’s a disturbing thought — it appears that over the past 30 years the distribution has shifted roughly up one sigma, so that what was 3 sigma is now about 2 sigma. Since it looks like the rise in mean temps is going to continue for at least another few decades, are we looking at what was 3 sigma events becoming 1 sigma and less? I know the there are calculations of the expected increase in the number of days above 90F or whatever, but this looks more frightening — somebody tell me what’s wrong with this reasoning. Please.
If you subtract the calculated expected physical warming based on the current attribution analysis would the climate system be expected to produce the same number of heat records as are now occurring on trend?
Survey says? No.
If you subtract (anthropogenic GHG’s, sulfates, ozone) the mean increase in RF due to human influence the model rather strongly suggests that the extremes would not be occurring.
As I said, reverse the null hypothesis. Prove current extremes are not human influenced. Good luck with that.
Voltaire: Le mieux est l’ennemi du bien. (The best is the enemy of the good.)
You seem to be foraging in the chaos of localized events in the noise to dissemble the significance of the anomaly trend in context of the historical trend. Do you really think that is scientifically wise when weighing the evidence in context of the supporting physics and probability analysis?
In other words, you are picking on “high amplitude and persistent ridging” as the red herring (short term events) to distract from the probability analysis (regarding the long term anomaly trend attributable to increased RF). Like I said, write a paper and get it to pass muster in a relevant peer review. Good luck.
“Folks…I know I am entering the lion’s den talking in this forum, but Hansen had no basis to say confidently that last summer’s heat wave was caused by global warming. …cliff”
Measurements of nature that affect human comfort are filled with value judgements like this (e.g. tropical cyclone strength categories). Technically all are arbitrary and approximate, yet they are useful.
It seems to me that the problem with your approach is that by the time the standard of proof is met everyone but historical climatologists will have ceased to care.
On your point about not wanting to give too much credit to global warming for the added increment of heat, here’s a very topical example where doing just that seems entirely appropriate. It turns out that the best metric of how the U.S. corn crop will do is the number of degree days exceeding 29C. The more of those there are, the worse the crop does. But the key point is that below that threshhold there is little damage. So in the instance of this season’s heat anomaly, why should global warming not get most of the credit?
Mr. afeman asks, insofar as i understand, if the NH JJA temperature distributions will continue evolving in a way similar to the last thirty years.
That is asking for a model forecast of the future course of climate evolution. I do not know what the models say in hindcasts over the past from 1931-2011 for the NH JJA distribution, nor what they predict. I will note that previous forecasts have, if anything, underestimated the speed and ferocity of the changes we see today.
…Generally heat waves, like the ones in the Midwest this year and last, are usually associated with high amplitude and persistent ridging. Now it is clear that GW can increase the background field—but the amplitude so far in the midlatitudes is modest (0 to 2 F perhaps, considering where you are). More in the Arctic. The background does not explain the amplitude Midwest heat waves. But there was clearly high amplitude and persistent ridge during the recent events. Now the question then becomes—is the excessive ridging the last two summers the result of GW?…
An excellent question, and refreshingly worthwhile for taking this conversation forward. Restating Cliff’s question, are mechanisms at play helping to make additional energy in the atmosphere inhomogeneously distributed? Is any given spot on Earth only going to experience the mean increase in temperature, as Cliff implies in his blog post, or can we expect differently?
Well, we know that energy is going appear in a lumpy form, at least if we accept that facts in the Arctic are not only accidentally coincident w/theory. But that’s not a matter of weather, it’s climate.
So what about shorter-wavelength features, weather? A brief search suggests there’s reason to entertain the possibility:
It might be nice to stop letting Cliff Mass suck up all the oxygen in the room, but before I take my own advice I’d like to observe that he appears to be confusing weather with climate. Since his part of the world has been mostly rather cool, he seems to think he knows better. Since the strongest indicator of opinion on global climate change is individual’s weather experience, isn’t that all to likely?
Comment by David B. Benson — 20 Aug 2012 @ 8:58 PM
I don’t think you’ve got this quite right:
“We have neither long enough nor good enough observational data to have a perfect knowledge of the extremes of heat waves given a steady climate, and so no claim along these lines can ever be for 100% causation, but the change is large enough to be classically ‘highly significant’.”
We certainly have long enough duration observations to know what three sigma is. Asking for a longer set only allows you to find out if the distribution near four or five sigma is non-gaussian since those events may not be well enough sampled at this point to tell. The mean and sigma just won’t change much with more data. But that knowledge about the five sigma event frequency really says nothing about causation. In our current crop of above three sigma anomalies, finding one that was not caused by warming is like finding a needle in a haystack, because we know the distribution is gaussian with regard to what three sigma is. Trying to find a five sigma event not caused by warming is not really relevant to the argument.
We don’t get to 100% causation because, over a long enough period of warming, we know there should be a needle in that haystack. Maybe one needle for every 30 straws of hay if we end emissions now. It does not have anything to do with trying to find a five sigma golden needle; for that you would need a very long period of warming indeed to get a large enough haystack to search through. Basically it is what we do know about the distribution, not what we don’t know (very rare wings) that tells us that we don’t get to 100% causation.
Susan, yeah. When one knows 7F + 1F = 8F (so the answer is 1/8, duh), then adding gobbledygoop just proves “you guys” don’t even know elementary school math, or you’re being deceitful. Yell, explain, teach all ya want, it’s not like you’re gonna prove 7F + 1F isn’t 8F. Unless…
Perhaps a way to squash this belief would be to subtract the global average increase in temperature and then calculate the sigmas. If Cliff is right, shouldn’t every decade essentially match the base period?
Doug Bostrom @87 asks are mechanisms at play helping to make additional energy in the atmosphere inhomogeneously distributed?
I assume the question is rhetorical, but just in case some reader is not yet sure, the answer is yes.
[reCAPTCHA agrees by proclaiming The yzeditu so now you know the reason.]
Comment by David B. Benson — 20 Aug 2012 @ 9:30 PM
Susan Anderson (#88): You’re charitable. I live in Pugetopolis as well, and we do have electricity and computers. In fact, not long ago, Cliff Mass was quoted in newspaper predicting that we would have more dreary foggy summer days due to global warming: Seattle Times, August 1, 2012. It’s a pattern we’re all used to, “marine push”. Anyway, it’s been a fine summer, so no excuse: July 2012 actual cf. average and August 2012 actual cf. average.
When one extreme event happens, we carry on, and recover. When two (or more) happen too close together, we struggle. When your house gets broken into, you think how unlucky you were. When it happens again, you start to question whether you should move to a different area, buy extra security etc.
So if climate related disasters happen too frequently, we will struggle psychologically.
90 Jim Larson wrote: “Perhaps a way to squash this belief would be to subtract the global average increase in temperature and then calculate the sigmas. If Cliff is right, shouldn’t every decade essentially match the base period?”
Yes. Similar to my 43 and 45. Clifford Mass’ hypothesis has nothing to do with “values”. It is fully calculable and the answer is sitting there in the data. The answer is in fact explicitly stated in Hansen’s PNAS in the first place: “In addition, the distribution has broadened, the shift being greater at the high temperature tail of the distribution.” and “This exposes the fact that the distribution is becoming broader and that there is a disproportionate increase of extreme hot outliers.”
The onus is on Clifford Mass to show precisely why this result of Hansen’s is wrong. If the only consequences of global warming were a uniform constant shift of temperature by the mean then the whole issue would be much less worrisome. The distinction between a shift of mean and a change in the distribution was hashed out in the letters to the editor section of my local newspaper 2 decades ago by two scientists. I am surprised to see it coming up now.
Comment by John E. Pearson — 21 Aug 2012 @ 3:49 AM
can someone comment on Dan Miller’s reply (reply #19), where he says:
> If this all wasn’t scary enough, +4-sigma events
> are now happening about 5% of the time and
> +5-sigma events, that formerly had a return time
> of about a million years , are now occurring
> about as often as 3-sigma events happened 50
> years ago. With further warming, +4 and +5-sigma
> events will become “normal”.
Comment by David M. Besonen — 21 Aug 2012 @ 5:00 AM
Prokaryotes, thanks for the posting of the link to the NASA animation of Hansen’s work. You shouldn’t really need to have much understanding of bell curves to see what is happening with this animation. However in some ways I have to agree with Cliff about what the public does understand. I would wager that something approaching 2 standard deviations of the population haven’t got a clue what a bell curve is, and who’s scientific and mathematical understanding is so poor that you would have to take a good half hour of one on one time to get a majority of them to grasp what a bell curve is and how it can be interpreted, and some never will. . The other problem is of course, it doesn’t matter how brilliantly you describe these matters to the lay population, if the media won’t give you room to do so. This is particularly true of television, which is where about 70% of the population get almost all their news and current affairs information; most folk could watch television for a million years and they’d still be no wiser, of course by then their brains would have dribbled out of their ears.
From Post #63 Now the question then becomes—is the excessive ridging the last two summers the result of GW? Was the large scale flow pattern somehow enhanced by GW? There is no reason to expect this…either from modeling or theoretical results
There is an excellent video explaining why this is the case here:
“Note that the change in spread shouldn’t be automatically equated with a change in climate variability, since a similar pattern would be seen as a result of regionally specific warming trends with constant local variability”
This seems like a distinction without a difference. Under this description, if you were to take a cut across a hardiness zone, you’d find regions where the hardiness description is less reliable owing to increased spatial variability. So, that would in fact be a change in climate variability.
Also, in the supporting link, the failure to reproduce the new paper’s results seem much more likely to be attributable to not using global data and not looking at summer time. If the mean shift is small compared to sigma then it is hard to say anything.
101 Eli wrote: “Second, if you put more energy into a system variability increases.
Third, if you put more energy into a system variability increases asymmetrically towards the direction favored by higher energy”
I’m not sure you meant this but the way those two points are stated makes it sound as if these statements are true in general, i.e. for systems other than the climate system. While I expect that they are true for the climate system it’s unlikely that they’re generally true as they would comprise new physical laws.
Comment by John E. Pearson — 21 Aug 2012 @ 11:27 AM
“There is no reason to expect this…either from modeling or theoretical results”
As you can see, Mass just waves away newer research showing the impact of melting arctic ice on NH atmospheric patterns. He feels the research is unconvincing, but I’ve yet to see him explain why. (If I’ve missed his explanation could someone point me too it?)
It’s not clear if he thinks it’s fundamentally flawed research, or just too new — e.g. not enough support from other studies/researchers. I wish he’d address this in his blog.
I applaud the fact that you link to Tamino’s explanation why the increased variance may simply be a natural artifact of regional variability and where the baseline was chosen, and *not* actual increased variability. Apparently not many people on this thread read it, or understood it.
The real blowback against Hansen has a lot more to do with the alarmist and scientifically unsupportable statements he makes in his op-eds at the WP and NYT. In this article you speak to how science communication to the public should occur, and I would submit that there is a lot more communication happening in these op-eds than the PNAS paper.
“To the contrary, our analysis shows that, for the extreme hot weather of the recent past, there is virtually no explanation other than climate change.”
“Sea levels would rise and destroy coastal cities. Global temperatures would become intolerable. Twenty to 50 percent of the planet’s species would be driven to extinction. Civilization would be at risk.”
Many of the cheerleaders hear may well agree with Hansen’s statements, made with absolute conviction and certainty, but I would venture to say that the consensus of scientists does not.
Cliff Mass, I can understand your point. Here is an article that would support your view. Blocking events have increased. Some think because of Global Warming but that may not be the case. There is a graph at the end of this article that shows blocking days in the North Atlantic since 1901 by decade. It clearly shows that the number of blocking events is variable by decade and that we are in a phase with more blocking days than the period of time used for the Hansen research of 1951 to 1980. Looking at the graph in the articl I am linking to, what were the frequency of heat or cold waves from 1921 to 1950 which show many more blocking days than the 1951 to 1980 time period.
‘Choose your leaders wisely’. I would say we ignore Hansen at our collective peril. All those scientist who think Hansen is being too alarmist have not put forward convincing arguments, as far as I know, why his reasoned suspicion of the risks of faster changes than the current scientific consensus allows for are not justified. As long as these suspicions are reasonable we should be precautious and take them seriously.
Comment by Lennart van der Linde — 21 Aug 2012 @ 4:30 PM
Case in point (verbatim):
GEOPHYSICAL RESEARCH LETTERS, VOL. 39, L16703, 7 PP., 2012
Trends in record-breaking temperatures for the conterminous United States
Standard methods of identifying record-setting trends are complex and not robust
Record low minimums decreasing, record high maximums increasing
Novel, simple method presented here will be useful for climate impact studies
Clinton M. Rowe
Department of Earth and Atmospheric Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
Logan E. Derry
Department of Earth and Atmospheric Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
In an unchanging climate, record-breaking temperatures are expected to decrease in frequency over time, as established records become increasingly more difficult to surpass. This inherent trend in the number of record-breaking events confounds the interpretation of actual trends in the presence of any underlying climate change. Here, a simple technique to remove the inherent trend is introduced so that any remaining trend can be examined separately for evidence of a climate change. As this technique does not use the standard definition of a broken record, our records* are differentiated by an asterisk. Results for the period 1961–2010 indicate that the number of record* low daily minimum temperatures has been significantly and steadily decreasing nearly everywhere across the United States while the number of record* high daily minimum temperatures has been predominantly increasing. Trends in record* low and record* high daily maximum temperatures are generally weaker and more spatially mixed in sign. These results are consistent with other studies examining changes expected in a warming climate.
#103 / John Pearson: 101 Eli wrote: “Second, if you put more energy into a system variability increases.
Third, if you put more energy into a system variability increases asymmetrically towards the direction favored by higher energy”
I’m not sure you meant this but the way those two points are stated makes it sound as if these statements are true in general, i.e. for systems other than the climate system. While I expect that they are true for the climate system it’s unlikely that they’re generally true as they would comprise new physical laws.
Eli thinks this is indeed a fairly general proposition rooted in statistical mechanics. All systems are constrained globally by conservation of energy but the possibility of local fluctuations depends on the amount of energy available locally, e.g. the distribution of energy in the system. The more energy in the system, the larger these local fluctuations can be. Examples can be found in many areas including protein folding and unfolding, molecular dynamics, etc. For example http://jcp.aip.org/resource/1/jcpsa6/v89/i9/p5852_s1
Many of the cheerleaders hear may well agree with Hansen’s statements, made with absolute conviction and certainty, but I would venture to say that the consensus of scientists does not.
Sure, because some guy said so on some blog. I guess that explains why many previous civilizations collapsed when their local climate changed as well, and their local sources of food and water became unreliable.
You understand the difference between local and global, right? You understand the difference between a few hundred or thousands of people having to evacuate their desert homes and seven to nine billion on a planet? I would venture to say you don’t have a clue about the physics and biology at play here.
> The more energy in the system, the larger these local fluctuations
I’d been trying to think of any case John P. could cite where you wouldn’t expect to see local fluctuations toward the high end while energy is being added, and toward the low end when energy is being removed. Short of a superconductor, anyhow.
Imagine a pot of water at 50C.
Drop in a block of iron at 1C; you’ll see fluctuations, bits of colder water coming off the cold iron and mixing. Nowhere does any of it go above 50C.
Instead drop in a block of iron at 99C; you’ll see some water almost at 99C swirling as the heat goes into the water — but none of it goes below 50C.
Example needed where change _isn’t_ in the direction suggested.
re John E Pearson (@103) and the “laws” concerning distribution of fluctuations in physical systems according to temperature (energy).
In general Eli’s postulates which you reproduce don’t constitute “new physical laws” since they’re already more or less contained within existing laws! Most notably Boltzmann’s law defining the distribution of states (that differ in energies) according to temperature.
According to Boltzmann’s law p ~ e^(-E/k.T), where p is probability of a state occurring, E is its energy and k is Boltzmann constant.
So as you increase the temperature of a system that is defined by a number of different states separated by different energies (a climate system, or perhaps a protein whose configuration in solution may be characterized by a set of fluctuations around the sort of structure one might observe in a crystal), you not only increase the variability by populating more states[*], but the distribution of sub-states shifts towards those that are favoured at higher temperature.
[*] Note that at any temperature all of the states exist according to the Boltzmann distribution. However according to an observer a particular state may not be apparent until it is sufficiently populated. Thus increasing the temperature may populate a particular protein fluctuational state at a level (say 1% of the total distribution) where it might be detectable spectroscopically…..and increasing the global temperature may increase the frequency of a particular climate state (e.g. a severe drought or heat-wave) so that it becomes annoyingly apparent.
In reality the climate system won’t accord strictly to Boltzmann’s laws of distribution of states due to it’s complexity and the possibility of threshold effects (phase changes)/feedbacks and so on. However this also applies to more simple physical systems like the protein..heat the protein sufficiently and it will undergo an abrupt phase change to an unfolded (denatured) state…
If those points are generally true then the constitute physical laws and their domain of validity ought to be specified, and of course they ought to have names Rabett’s second and third laws, I guess. I’m not sure they’re true in the case of hard turbulence.
Comment by JOhn E Pearson — 22 Aug 2012 @ 10:51 AM
117 Chris wrote about Boltzmann statistics:
The connection to equilibrium statistical mechanics is opaque because we’re talking about driven systems far from equilibrium. At least that is what I thought we were talking about.
Comment by JOhn E Pearson — 22 Aug 2012 @ 10:53 AM
It sounds plausible that a system with higher energy has greater variability, but under what conditions? And with what held constant? Is there a theorem about this, or is it just a plausibility argument? (And is this actually claimed as a general theorem in the Hansen article, as the summary in @101 seems to imply?)
Consider a box willed with gas, under two conditions: (1) the first box is in equilibrium, at high temperature, and thus has a high energy content; (2) the second box has low energy content, but is out of equilibrium: it is stirred by turbulent convection, produced by heating from below and cooling from above. Which box has more hydrodynamic fluctuations (i.e., weather)? It seems plausible to me from this thought experiment that while the amount of energy may affect the size of the fluctuations, the degree of disequilibrium is also important in determining their size.
@114 Hank Roberts. Here is an example of a system where there is locally a change in the wrong direction. Suppose we have a block of iron and a beaker of water, initially at the same temperature. The iron and the water are connected to a heat engine which is connected to an air conditioner in a room also at the same initial temperature. Now we add energy to the system by heating the iron block. The temperature of the room (and the energy in it) decreases. While this particular situation might not occur by chance in nature, it shows that it is not a law of nature that if you add energy to a system, all sub-parts of the system experience only fluctuations in the same direction.
Tom Scharf @105 ends his comment “Choose your leaders wisely.”
This may be indeed a criticism of Hansen who attempts instead (in one of the Op-Eds that Tom Scharf quotes from) to get action from a reluctant leader. “President Obama speaks of a “planet in peril,” but he does not provide the leadership needed to change the world’s course.”
However the actual brickbats Tom Scharf tosses in are far from well aimed.
The first Hansen Op-Ed quote Tom Scharf objects to begins “To the contrary…” so presumably Tom Scharf is more at ease with what is being disavowed by Hansen when he said “…it is no longer enough to say that global warming will increase the likelihood of extreme weather … (nor) to repeat the caveat that no individual weather event can be directly linked to climate change.” I suppose Tom S. thinks it still remains “enough to say…” That’s fine by me. It will always take some folk a bit of time to catch up with the game.
The second Hansen Op-Ed dates from May 2012 and the apocolyptic prediction is about a world following continued oil/coal/gas use as well as exploited tar sands. So this is what? 750ppm of atmospheric CO2? I would be difficult to argue that such a level would fail to leave a big legacy like flooded cities etc.
That is not to let Hansen off without a better aimed brickbat. He says “…concentrations of carbon dioxide in the atmosphere eventually would reach levels higher than in the Pliocene era, more than 2.5 million years ago…” Surely this is an error. It should be Paleogene 34 million years ago and you are not going to get full marks with mistakes like that.
80 Jonathan asks, “Is there any simple way that doesn’t do violence to the data to plot temperature on the x-axis instead of standard distributions?”
No. On Vancouver island, a 10 degree increase in temperature is astounding, but in Pheonix it’s a yawner. Since Vancouver Islanders often live without owning AC, such a change is more important than it would be in Pheonix. So, by using sigma instead of temperature, you automagically warp the data into something important to people.
(1) IF you consider the distribution of a sum of independent gaussian random variables the variance is the sum of the variances of the individual variables. Differences in the means don’t affect the variance. If I’ve understood Tamino he considered dependent variables. In particular he considered a distribution, p(x) which was a sum of distributions, p_i(x), with arbitrary means. In that case the variance of p is the arithmetic mean of the variances of the p_i + contributions due to differences in the means. It seems to me that one ought to be trying to ascertain the dependence/independence of different sites?
(2)That being said it becomes clear that Clifford Mass’ claim that you can only attribute the global mean anomaly to local heat waves is clearly wrong too. If it is correct that you can only attribute changes in mean temperature to heat waves it ought to be the change in the local mean, for example the anomaly in a particular region for a particular month averaged over, say, the last decade. Local anomalies can be much larger than the global anomaly because some places are warming more than others as everyone knows.
Comment by JOhn E Pearson — 22 Aug 2012 @ 11:34 AM
John @119, the connection to equilibrium statistical mechanics isn’t so opaque I think.
If we forget about enhanced greenhouse forcing (say the climate system has come to equilibrium with respect to enhanced greenhouse forcing), then a local seasonal climate will be characterised by a distribution of states that we might consider the equilbrium (e.g. so many days of such and such a temperature with characteristic minimum and maximum temperatures, some sort of charactersitic rainfall and wind patterns etc.). That’s pretty much what climate is at the local scale.
Now make the Earth’s global temperature warmer. This will shift the distribution of states on the local scale to a new equilibrium (i.e. a new climatology).
Of course where this differs from a true Boltzmann relationship is the presence of non-linear effects, thresholds, phase changes and complex second order effects that I referred to in my post. For example tropical storms (hurricanes) don’t form unless the sea surface temperature reaches a threshold temperature (~26.5 oC according to William Gray) and the while the hurricane wind speed increases around 5% for each 1 oC of temperature rise, the destructive power in monetory terms increases with something like the cube of the wind speed (e.g. Emanual Nature 436, 686 (2005)).
However we expect Rabbet’s laws of distribution of climate states to apply. Just like the distributions under Boltzman’s laws, the number of detectable states will increase (increased variability) and states characterstic of higher temperature will take an increasing share of the distribution as the temperature rises. That’s certainly what one expects in he majority of local climatologies in a warming world, although of course the local response to global warming will be larger in some areas than other and etc…
I see that my attempt to put in greater than and less than signs mangled my post. Let me try again.
Consider a system having a phase transition a temperature Tc, initially at temperature T less than Tc and I increase the temperature toward Tc. I will observe fluctuations which are correlated over large and larger regions of space and time, and increased variability.But this will also occur if I begin at T greater than Tc and _decrease_ the temperature toward Tc.
I am not implying that the global climate system may be close to a phase transition, but as we see, large parts of the Arctic Ocean are evolving toward seasonal ice free state.
John E. Pearson: On Vancouver island, a 10 degree increase in temperature is astounding, but in Pheonix it’s a yawner. Since Vancouver Islanders often live without owning AC, such a change is more important than it would be in Pheonix.
Phoenix is just concluded a heatwave setting records for consecutive days above 110F, perhaps more importantly nights not falling below 90F. Some local produce truck markets have suspended operations due to the impact on crops, won’t be operating again this year. The heat was a distinct hazard or even showstopper on construction sites and at other places where people must work outdoors.
Temperatures were about 10F above normal during this event.
Before anybody begins yapping about specific attribution (sophisticated meteorologists tell us that such record-breaking sequences are perfectly in keeping with an unchanging climate), I mention this as an example counter to Jim’s implication that living in a place with a torrid climate toughens the local culture. I’d offer that while that may be true, there’s also precious little headroom available.
125 Hank, I guess I don’t understand the constraints of the puzzle you posed. I thought that your challenge was to add energy to a system, and cause the temperature of some sub-part system to decrease spontaneously. Heat pumps do operate spontaneously, if you have a high temperature reservoir and a low temperature reservoir, so I don’t know why you would exclude them from the solution to your puzzle, but I’ll try again without using a heat pump.
My system is a balloon, a pulley, a rope, a rock, and the atmosphere. The balloon starts on the ground at neutral buoyancy. I raise the rock (adding energy to the system) and tie it to the rope. The rock then falls back to Earth, lifting the balloon. The balloon expands as it rises, losing energy by doing work on the atmosphere, and cooling adiabatically.
I suppose there are much simpler solutions to the problem I’ve attempted to address, which makes me think that I still haven’t understood what the question is.
This doesn’t seem to be related to the question of how to refrigerate the Earth as a whole. There is a low temperature reservoir available (outer space), but the problem, or so it seems to me, is that our thermal contact with it is poor, being essentially limited to radiation from the upper atmosphere. So what we need to do is to add giant heat sinks to the Earth, yes?
But this seems distant from the original topic of whether or not increasing the energy in the atmosphere leads to wider (or even counter-varying) variations in the local weather, which only requires energy transport within the system.
Chris in 124 went back to the specific case of “climate states” but Eli’s original phrasing was not climate-specific and it is the general claim that I have trouble with, not the specific case of climate. In any event I don’t want to be guilty of hijacking the thread any further off-topic.
Mike P.: So what we need to do is to add giant heat sinks to the Earth, yes?
Well, we already have a giant heat sink connecting Earth to space, a free gift, but we’re busily degrading its efficiency.
“I’m too warm because I’m wearing a sweater. I’ll put on another sweater, then call in a ventilation contractor to install air conditioning. While they’re doing their work and taking my money, I’ll continue bundling up with more sweaters.”
Not to pick on Mike P. but that’s a totally crazy path to take, unless we’re prepared to give up on ending our relationship with hydrocarbon slaves.
dbostrom “…living in a place with a torrid climate toughens the local culture. I’d offer that while that may be true, there’s also precious little headroom available.”
Absolutely. When we had our “once in 3000 years” heatwave a few years ago, it was at the same time as our major arts festival. Normally, there are thousands of people wandering, and bustling, around night and day to various events and installations. Skipping around all the crowded pavement cafes.
After a few days (we’re quite accustomed to a few days here and there of 38C+, but in summer not autumn), the whole city became like a ghost town on minimum speed. No building or other outside workers, lots of outdoor events cancelled. When it got to a fortnight, it was like the place had switched off. And people died.
Reading the paper, it is hard to find the three points that Eli gives in #101 within the paper. There is a QED point in the post publication discussion that sounds a little like Eli’s first point, but neither of the other two points seem to be touched on.
I would say that the chief point of the paper is:
“The climate dice are now loaded to a degree that a perceptive
person old enough to remember the climate of 1951–1980 should
recognize the existence of climate change, especially in summer.”
What we exprience directly as weather is also now a direct experience of climate change when we undergo heat anomalies. The variability that used to disguise climate change is now making it apparent.
When looking at PDFs that seem more-or-less-normal, it would be really nice to compute mean, S.D., skew and kurtosis, and maybe do a normality test.
I.le., first 4 moments.
As noted in the post, there may well not be enough data to be significant,
but when these are not shown in a little table, people sometimes make comments about whether or not a curve is skewed or tails weighted more heavily or not.
An author might explicitly say: there is not enough data to say anything meaningful about skew or tail-weighting, but if people are going to discuss those anyway, it seems helpful to compute the 3rd and 4th moments along ith the first two, rather than leaving it to eyeballs.
Thank you John Mashey for the pointer -into- the long Tamino thread. It stays interesting for quite a while after that (with a few excursions). Seems to reach a bottom line where MT comments and Tamino replies.
My brief excerpt of that:
MT: … This all said, would you agree that none of it matters in terms of the lesson for policy?
T: [Response: Yes.]
MT: With respect to baseline statistics, severe hot outliers are increasing to an impressive extent. That’s what matters no matter how you slice it. It’s important not to confuse an academically interesting disagreement with one that has practical policy implications.
T: [Response: I agree that pretty much any method will be prone to confusing trend and variation. Still I think it's an issue worthy of closer inspection -- as an academically interesting problem. From a practical policy viewpoint, any way you slice it severe hot outliers are increasing.]
140: This is not a mere academic challenge. It is important to quantify the the level to which the current weather has been influenced by climate change. Policy requires some level of agreement on the science. You can’t expect a group of policy makers (roughly half of whom don’t believe in anthropic warming no matter what the science says) to make policy if an iron clad case hasn’t been made that we’re seeing the effects of climate change now. For every op-ed piece Hansen writes Lindzen writes one saying the opposite.
Jim: For every op-ed piece Hansen writes Lindzen writes one saying the opposite.
We desperately need for Lindzen to be authoritatively contextualized, pronounced upon. Yes, there would be a hue and cry but that clamor would necessarily put Lindzen’s activities under the spotlight. “Why are they picking on poor Lindzen? Let’s take a look.” No pain, no gain.
Isn’t it remarkable that Hansen writes an op-ed with an apparent peripheral glitch poking out of a bulky and dire implication and the glitch becoming the topic of the day, while Lindzen can claim in his respective op-ed that there’s no recent statistical anomaly in record temperatures and get away with it without a peep?
An error versus… what? An oversight? Abject ignorance while speaking as an authority? Worse?
Enough of wrong with no opportunity costs, already. Great research done 40 years ago isn’t a free pass to waltz around the world changing governments in pursuit of romantic economic fantasies.
Lindzen is the Moby-Dick of this fiasco, drives some of us crazy.
142 dbostrom called me Jim and said: “Isn’t it remarkable that Hansen writes an op-ed with an apparent peripheral glitch poking out of a bulky and dire implication and the glitch becoming the topic of the day”
I believe what you are calling a “peripheral glitch” is the artifactual broadening of the anomaly distribution which Tamino suggests is due to spatial variance.
Hansen said in the opening paragraph of the first section, “Principal Findings” of the Discussion: Seasonal-mean temperature anomalies have changed dramatically in the past three decades, especially in sum- mer. The probability distribution for temperature anomalies has shifted more than one standard deviation toward higher values. In addition, the distribution has broadened, the shift being greater at the high temperature tail of the distribution.”
By my reading this is dead center. If it is really self-evident that the temperature extremes have gotten enormously hotter then there ought to be a valid analysis indicating that.
Comment by John E. Pearson — 24 Aug 2012 @ 7:37 AM
>> John E Pearson says: …
>> 140: This is not a mere academic challenge….
>> Policy requires … an iron clad case ….
Sorry, John, but you’re expressing hopelessness about politics there, which is not the same thing as assessing the question Tamino and MT are talking about.
The question Tamino raised is, as he says, an interesting academic one, which Hansen may want to think hard about while continuing to revise the paper — remember it’s a draft paper for comment. The thread at Tamino’s is comments on the draft. This is how science works.
When you say policy requires iron clad science papers, you’re dismissing the use of statistics — which is how the deniers work, they insist on the impossible.
It’s an interesting academic question Tamino raised over there — a question that doesn’t affect the implications of Hansen’s paper for policy, for any values of policy that rely on sensible consideration of the real world.
Yes, today, in the USA, policy decisions aren’t being made. Period.
No “iron clad” presentation is going to change the denial.
Work to get the science and statistics done right, including uncertainty.
Work on the politics where that work can be productive.
We need better politicians, not “iron clad” science.
I don’t see anything in either Hansen’s PNAS paper or discussion paper that accords with your assertion about temperature extremes:
“By my reading this is dead center. If it is really self-evident that the temperature extremes have gotten enormously hotter then there ought to be a valid analysis indicating that.”
Hansen doesn’t say/show that “temperature extremes have gotten enormously hotter”. He shows that hot/very hot temperatures (> 3 sigma) constitute a much higher proportion of the temperature distribution, and that the spatial extent of hot/very hot periods have considerably increased.
But I don’t see that this interpretation requires that temperature extremes have gotten hotter at all (let alone “enormously hotter”). For example since the temperature anomalies used in the analyses are local seasonal averages, then an increase in the value of a temperature anomaly might arise simply from a shift in the local temperature distribution. One could model an increase in a local summer anomaly of 21 oC (in 1951, say) to 24.6 oC (in 2011) by a shift in the seasonal distribution of 18 oC cool days and 28 oC hot days from a ratio of 2 in 1951 to 0.5 in 2011. No increase in maximum temperature at all, but a large effect on the anomaly.
Of course temperature extremes have gotten hotter as we can observe in the temperature records. But the point is that the analysis doesn’t indicate “temperature extremes have gotten enormously hotter” at all, and the “valid analysis” that indicates that temperature extremes have gotten a bit hotter are readily apparent simply by inspection of local temperature series.
The point about increased variability is a rather minor one I would have thought. I suspect that the increased variability relates to the global (or hemispheric) scale and not necessarily the local scale as others have indicated (including the top article).
In 144 I used the phrase “temperature extremes have gotten enormously hotter” which I meant as a paraphrase of Tamino who wrote: “any way you slice it severe hot outliers are increasing.” I submit that my phrase was not a severe distortion of Tamino’s meaning.
Everyone seems to claim that that hot outliers are increasing and that this is self-evident. I believe it might be so, but I’d like to see a published analysis.
Chris wrote “The point about increased variability is a rather minor one I would have thought.”
I think that a result presented in the 3rd sentence in the first paragraph of a section entitled “Principal Findings” is being presented as a principal finding of the manuscript in question.
Chris wrote “then an increase in the value of a temperature anomaly might arise simply from a shift in the local temperature distribution.”
I agree. It might. I suggested that in 123. I don’t know that anyone has done such an analysis. What seems reasonably clear to me (based on Tamino’s analysis and the discussion) is that Hansen’s analysis generates spurious variance. You cannot use the spurious variance to attribute hot outliers to a changed distribution.
You can play around with these maps to get some idea of where the local mean is higher. http://data.giss.nasa.gov/gistemp/maps/ but you quickly get to the point where “playing around” is inadequate.
“the “valid analysis” that indicates that temperature extremes have gotten a bit hotter are readily apparent simply by inspection of local temperature series.”
You can’t tell anything about the statistics of hot outliers by simple inspection of local time series. Statistical analysis is required. I once flipped 10 consecutive heads. My immediate response was that there was something wrong with the coin. 90 flips later the coin looked fair. If you can demonstrate that the outliers imply that the distribution is altered beyond a simple shift of the mean in a statistically meaningful way you should write it up and publish it.
Comment by John E. Pearson — 24 Aug 2012 @ 4:05 PM
to again quote Isaac Held (cited earlier), consider two descriptions that sound very different:
“the ‘number of very hot days increases dramatically’
‘the number of very hot days does not change but they are on average \delta T warmer’”
[and then he writes]
“My gut reactions to these two descriptions of the same physical situation are rather different. The goal has to be to relate these changes to impacts (things we care about) to decide what our level of concern should be, rather than relying on these emotional reactions to the way we phrase things.”
147 John said, ” If you can demonstrate that the outliers imply that the distribution is altered beyond a simple shift of the mean in a statistically meaningful way you should write it up and publish it.”
The shapes of the distribution curves has changed each decade as the mean has increased, so Hansen’s paper does show exactly that. Now, as I suggested earlier, subtracting the median change (local, regional, global?) before assigning the sigma rating would explicitly show the result you’re asking for. I hope some kind statistician does such an analysis.
I think that ultimately that this comes down to whether the temperature at different sites is independent or not. The central limit theorem says that the distribution of the mean of a bunch of independent random variables tends to be gaussian with variance that is the sum of the individual variances.
This is a fairly general result but you can’t relax the independent condition. My interpretation of Tamino’s discussion (particularly the 3rd and 4th figures here: http://tamino.wordpress.com/2012/07/21/increased-variability ) is that Hansen lumped together dependent variables and treated them as independent. I don’t think this means Hansen’s paper shouldn’t have been published but it means that the method he used to ascertain variance generates spurious variance so that that aspect of Hansen’s analysis is flawed.
Comment by John E. Pearson — 25 Aug 2012 @ 9:14 AM
Hank in 148 linked to a very interesting discussion and asked “So — what does the data show?”
It is incredibly difficult to tease out changes in the shape of distributions from such small amounts of data. I believe that these temperature extremes, heat waves, etc are a consequence of global warming, but that is a belief. Before the economic collapse I believed we were in a housing bubble. When I casually observed housing prices I could see a spike. Paul Krugman wrote for years before the collapse that we were in a bubble and I believed he was right. Alan Greenspan didn’t. I don’t think Greenspan was an idiot. I think that there was no rigorous analysis demonstrating that we were in a bubble possibly because a rigorous analysis is impossible with such small amounts of data. You look at a short stochastic time series and say “Gee prices are going up awfully fast.” or “Gee, temperatures are going up awfully fast” but showing that such increases are statistically meaningful is hard when you have a time series of about 130 years or so and want to argue in a statistically rigorous way that the last few decades are special. I think that doing this on the basis of time series analysis is somewhere between hard and impossible. I think more and better analyses are needed. I predict that no one will argue with that.
Comment by John E. Pearson — 25 Aug 2012 @ 9:58 AM
I agree with you completely. While we may think something will happen based on the evidence, drawing a conclusion will require more data. This can be confirmed (or refuted) with mroe and better analyses.
“…but you can’t relax the independent condition.” John E. Pearson — 25 Aug 2012 @ 9:14 AM
But if you impose a forcing (AGW) which changes the degree of independence, making the tails fatter/less Gaussian, doesn’t that mean the forcing ACTUALLY makes the probability of what were once 3,4,5 sigma events MUCH higher than indicated by tamino’s method of analysis, which removes these effects? Doesn’t using a “baseline for anomaly calculation” “equal to the time span being analyzed” decrease REAL extreme weather event probabilities much the same way as using a sliding baseline minimizes the slope of temperature increase? This appears to me to be using Middleton’s Method for Minimizing Risk.
reCAPTCHA – “spread thatdo” – Yes, it do spread that distribution &:>)
As a newby here, I want to raise an issue I haven’t seen addressed. The thrust of the present discussion, and most discussions I have seen related to climate change, is the effect of climate on weather. The long-term trend of temperature increase appears to enable more extreme weather events, covering a number of different definitions of ‘extreme’. But, what about the impact of weather on climate?
Because of the potential non-linearity, or non-hysteresis, of extreme events, mechanisms could be triggered by these extreme events that could impact climate. These are over and above those positive feedback mechanims triggered by evolving climate mechanisms. One could postulate, for example, an overly warm Arctic week that crosses a threshold and triggers a burst of methane that would not be triggered at even slightly lower temperatures. This, of course, would add GHG to the atmosphere, feeding into further warming. So, it appears there is a symbiosis between climate and warming, each feeding upon the other to exacerbate the situation. Is this weather-climate symbiosis considered in the models?
I am reading the book “Hockey Stick and the Climate Wars”. My 8-year-old asked what it is about and I did not know how to respond without overwhelming him. Can you recommend any books that are truthful about the upcoming effects of climate change that I can read to my son?
8 years is too young to be given ownership of this problem. Stick to generally modeling good values instead, that’s my advice. Or failing that, make a plan for communications that isn’t the equivalent of emptying a bag of hammers over a young mind.
Repeating some remarks I made at P3, my son was the inadvertent subject of well-intended willy-nilly environmental destruction narratives delivered by his parents, various teachers, NPR, the “Planet Earth” documentary, IMAX movies, nearly every magazine he picks up, etc. etc. etc.
The healthy response to this is to let the snorkel valve rise to the “flooded” position and shut off the source of emotional drowning. My son has his valves shut now, presumably will crack the hatch and peek out at some point in the future.