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A warming pause?

Filed under: — stefan @ 6 October 2009 - (Español)

The blogosphere (and not only that) has been full of the “global warming is taking a break” meme lately. Although we have discussed this topic repeatedly, it is perhaps worthwhile reiterating two key points about the alleged pause here.

(1) This discussion focuses on just a short time period – starting 1998 or later – covering at most 11 years. Even under conditions of anthropogenic global warming (which would contribute a temperature rise of about 0.2 ºC over this period) a flat period or even cooling trend over such a short time span is nothing special and has happened repeatedly before (see 1987-1996). That simply is due to the fact that short-term natural variability has a similar magnitude (i.e. ~0.2 ºC) and can thus compensate for the anthropogenic effects. Of course, the warming trend keeps going up whilst natural variability just oscillates irregularly up and down, so over longer periods the warming trend wins and natural variability cancels out.

(2) It is highly questionable whether this “pause” is even real. It does show up to some extent (no cooling, but reduced 10-year warming trend) in the Hadley Center data, but it does not show in the GISS data, see Figure 1. There, the past ten 10-year trends (i.e. 1990-1999, 1991-2000 and so on) have all been between 0.17 and 0.34 ºC per decade, close to or above the expected anthropogenic trend, with the most recent one (1999-2008) equal to 0.19 ºC per decade – just as predicted by IPCC as response to anthropogenic forcing.

GISS temperature trends

Figure 1. Global temperature according to NASA GISS data since 1980. The red line shows annual data, the larger red square a preliminary value for 2009, based on January-August. The green line shows the 25-year linear trend (0.19 ºC per decade). The blue lines show the two most recent ten-year trends (0.18 ºC per decade for 1998-2007, 0.19 ºC per decade for 1999-2008) and illustrate that these recent decadal trends are entirely consistent with the long-term trend and IPCC predictions. Even the highly “cherry-picked” 11-year period starting with the warm 1998 and ending with the cold 2008 still shows a warming trend of 0.11 ºC per decade (which may surprise some lay people who tend to connect the end points, rather than include all ten data points into a proper trend calculation).


Why do these two surface temperature data sets differ over recent years? We analysed this a while ago here, and the reason is the “hole in the Arctic” in the Hadley data, just where recent warming has been greatest.

Mean temperature difference between the periods  2004-2008 and 1999-2003
Figure 2. The animated graph shows the temperature difference between the two 5-year periods 1999-2003 and 2004-2008. The largest warming has occurred over the Arctic in the past decade and is missing in the Hadley data.

If we want to relate global temperature to global forcings like greenhouse gases, we’d better not have a “hole” in our data set. That’s because global temperature follows a simple planetary heat budget, determined by the balance of what comes in and what goes out. But if data coverage is not really global, the heat budget is not closed. One would have to account for the heat flow across the boundary of the “hole”, i.e. in and out of the Arctic, and the whole thing becomes ill-determined (because we don’t know how much that is). Hence the GISS data are clearly more useful in this respect, and the supposed pause in warming turns out to be just an artifact of the “Arctic hole” in the Hadley data – we don’t even need to refer to natural variability to explain it.

Imagine you want to check whether the balance in your accounts is consistent with your income and spendings – and you find your bank accounts contain less money than you expected, so there is a puzzling shortfall. But then you realise you forgot one of your bank accounts when doing the sums – and voila, that is where the missing money is, so there is no shortfall after all. That missing bank account in the Hadley data is the Arctic – and we’ve shown that this is where the “missing warming” actually is, which is why there is no shortfall in the GISS data, and it is pointless to look for explanations for a warming pause.

It is noteworthy in this context that despite the record low in the brightness of the sun over the past three years (it’s been at its faintest since beginning of satellite measurements in the 1970s), a number of warming records have been broken during this time. March 2008 saw the warmest global land temperature of any March ever recorded in the past 130 years. June and August 2009 saw the warmest land and ocean temperatures in the Southern Hemisphere ever recorded for those months. The global ocean surface temperatures in 2009 broke all previous records for three consecutive months: June, July and August. The years 2007, 2008 and 2009 had the lowest summer Arctic sea ice cover ever recorded, and in 2008 for the first time in living memory the Northwest Passage and the Northeast Passage were simultaneously ice-free. This feat was repeated in 2009. Every single year of this century (2001-2008) has been warmer than all years of the 20th Century except 1998 (which sticks out well above the trend line due to a strong El Niño event).

The bottom line is: the observed warming over the last decade is 100% consistent with the expected anthropogenic warming trend of 0.2 ºC per decade, superimposed with short-term natural variability. It is no different in this respect from the two decades before. And with an El Niño developing in the Pacific right now, we wouldn’t be surprised if more temperature records were to be broken over the coming year or so.

Update: We were told there is a new paper by Simmons et al. in press with JGR that supports our analysis about the Hadley vs GISS trends (sorry, access to subscribers only).

Update: AP has just published an interesting story titled Statisticians reject global cooling, for which they “gave temperature data to four independent statisticians and asked them to look for trends, without telling them what the numbers represented”.


456 Responses to “A warming pause?”

  1. 151
    Patrick 027 says:

    OT but … I wanted to send a friend the web address for the “FAQ on climate models” parts I and II; I found part II but part I is missing – there is this website:
    http://www.realclimate.org/index.php/archives/2008/11/faq-on-climate-models/
    but it is not what it should be. Where did it go?

  2. 152
    Rod B says:

    Mark, if you don’t know the difference between making a guess — even a smart one, and having an sensor error in an actual measurement, I suggest, in Hank’s words, you google it.

  3. 153
    Jim Steele says:

    I am confused by just what natural variability means and how it can cause a cooling trend. It would appear that it depends on how what is being measured. If increased greenhouse gases are increasingly trapping heat, then that heat doesn’t disappear due to variability, or does it?

    This flattening of temperatures reflects surface temperatures. Therefore if these gases are trapping heat 1) I would expect the the total ocean heat content to still be increasing, despite declines in the average of surface temperature caused by natural variability. Is that true?

    or 2) If natural variability means that there is a mechanism that allows heat to escape, so that ocean heat content also flattens or drops, then I don’t see how the heating trend can just resume. I would only expect that with natural variability, the greenhouse gases trap heat during warming years and that merely balances out the lost heat during cooliong years. Can you explain how natural variability works more specifically?

  4. 154
    Martin Vermeer says:

    Paul Clark #126: see http://tamino.wordpress.com/2009/08/17/not-computer-models/
    Summary: lull in volcanism, bit of solar, and — yes — some CO2.

  5. 155
    Hank Roberts says:

    Jim, experiment.

    Take a glass of water, some ice cubes, and a thermometer.

    Put the ice in the water and the thermometer in the water.

    Check the temperature.

    Put the whole thing on a table and watch it for a while.

    The ice melts.

    The temperature doesn’t change.

    What’s happening?

  6. 156

    Jim Eager <a href="http://www.realclimate.org/index.php/archives/2009/10/a-warming-pause/comment-page-3/#comment-137710"#149. Another thing now you’re on the Medieval Warm Period: I’ve found a lot of data suggesting higher temperatures at different parts of the world, but when I line up the dates, they often don’t match. So there’s a case that there were multiple periods of regional warming, but not one single warm period. Ironically I found this at a denial site, where they were trumpeting this great find of dozens of papers to support their case (apparently a conspiracy to suppress all this evidence; some conspiracy if a bunch of amateur bloggers and retired scientists found so many papers). Sadly they did not appear to be able to assemble their own evidence and weigh it up.

  7. 157

    Jim Steele #153: the key thing to understand is that natural variability is not a trend: it’s blips that get cancelled out by other blips.

    There’s a great tool on Macs called Grapher. If you have a Mac, plot yourself sin x + 0.02x. Look at it in a highly zoomed in scale, and it looks like sin x. Look at it at a highly zoomed out scale, and it looks like y = 0.02x (a slowly rising straight line).

    Now think of the weather as having short-term cycles like sin x that vary up and down, but average out to zero, and climate change as a function that long-term looks like 0.02x. As with our graph, periods where the natural cycle goes down enough to overwhelm the long-term trend don’t count. The long-term trend is there in that the “down” phases of the cycle don’t go down as far as they otherwise would. If the sun puts out less energy, the earth will cool (low point of the solar cycle). If we have extra CO2 in the atmosphere that cooling will be reduced. If we have a big La Niña, the earth will cool – but not as much with extra CO2.

  8. 158
    Radge Havers says:

    Jack #119

    You can pounce on high-profile skeptics if you want

    So in other words, “carry on?”

    the average citizen that remains skeptical makes a good point

    No, they probably don’t really have a point. As long as people expect to get news from infotainment, they will have those expectations disappointed. I wish you could just turn on your trusty TV and get a one-stop-shop for reliable, intelligent and unbiased information in digest form. The reality is you can’t be a passive consumer of news AND be well informed. That’s just the way it is these days.

    So quit waging war like this, as if the real problem is that everyone is stupid, except for you.

    Um, I’ll admit that the heat surrounding this issue can be a little disconcerting, but I think it’s fair to say that there’s no assumption here that “everyone” is a stupid enemy. In fact, it seems to me that your hostile rebuke assumes that the scientists and others visiting this site are too stupid to understand the nature of the political attacks on AGW.

  9. 159
    Jim Steele says:

    Hank I am not sure what your point is. Are you attributing natural variability to latent heat? Are you saying that the flattening of global surface temperatures is due to heat latent heat absorbed as ice melts? That makes limited sense. During this flattening/cooling trend, there has not been any dramatic increase in melting glaciers and global sea ice has been increasing the past 2 years.

    I think your logic is too simplistic, For example southern hemisphere ice has been significantly increasing the past years http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.anom.south.jpg
    So why couldn’t I equaly argue that the latent heat released as the sea ice increases is masking a real cooling trend?

  10. 160
    oakwood says:

    My prediction: The next IPCC report will either (i) replace the HAD CRU graph with the GISS graph or (more likely (ii) combine them together. Option (i) would look just a bit too much like picking the result that fits the argument.

  11. 161
    Mark says:

    Bob Bob, if you don’t realise that interpolating between two values IS a guess, your capabilities in the lab are seriously hampered.

  12. 162
    Mark says:

    CTG in 176 proclaims:

    “The problem is that there are a lot of people who insist that the only two options to see if the plug is live are:

    a) touch it to see
    b) burn the house down to be safe”

    I think the number of people who do that figure into “a handful” at most. Out of the 6+Billion on the planet.

    I.e. to all intents and purposes: nobody.

    I.e. your point is bull.

  13. 163
    Paul Clark says:

    pjclarke @ 137: WFT data is all monthly, so actually that link doesn’t include any mythical Oct/Nov/Dec 2009 data, it just gives you the last 111 months, from June 2000. I suspect the poster was trying to get all data from 2000 – not sure why they didn’t use 117 if it was posted recently – so “from:2000″ would have been easier. The funny thing is, using “last:111″ on a live linked graph means that the graph will change as time goes by, so in a few year’s time it may go directly against the point they were trying to make. An interesting problem for historians… :-)

    Jim Eager @ 148: Thanks for your response and useful links – I chose 1910-1940 because it’s a 30 year period, and joins to the 1940-1970 period that someone else was talking about re cooling above. As you point out, if you go to 1945 the trend is even higher.

    I was aware of the acceleration of C02 and that linear trend wasn’t quite right, but I had also guessed (wrongly) that there was a step change shortly after WWII which would compensate for it – but your link shows this isn’t the case, thank you. Clearly the change in C02 over the period isn’t anything like what’s happened in the last 30 years, but it’s definitely there.

    On solar… Looking at sunspot numbers as a proxy, there was indeed an upward trend 1910-1940, but the much larger 11-year cycle has only a small effect on temperature (it is there in the noise if you filter for it) – or is this an issue of thermal inertia? Is the 11-year cycle being low-pass filtered by the Earth, so only the long-term trends remain?

    http://www.woodfortrees.org/plot/hadcrut3vgl/from:1910/to:2000/mean:36/plot/hadcrut3vgl/from:1910/to:1940/trend/plot/hadcrut3vgl/from:1940/to:1970/trend/plot/hadcrut3vgl/from:1970/to:2000/trend/plot/sidc-ssn/from:1910/to:2000/scale:0.01/mean:36/plot/sidc-ssn/from:1910/to:1940/trend/scale:0.01/plot/sidc-ssn/from:1940/to:1970/trend/scale:0.01/plot/sidc-ssn/from:1970/to:2000/trend/scale:0.01

    Martin Vermeer @ 154 also mentions a lull in volcanism as a cause of the 1910-1940 rise… Are there datasets for this I could put on WFT? What do they actually measure?

  14. 164
    Alan Ross says:

    “It does show up to some extent (no cooling, but reduced 10-year warming trend) in the Hadley Center data”
    Perhaps we should look at the Hadley graph, seems to show an accelerating cooling trend for the past 4 years!
    http://hadobs.metoffice.com/hadcrut3/diagnostics/comparison.html

  15. 165
    CTG says:

    Re #162 Mark.

    I’m not a denialist.

    You don’t need to put me down.

    I was agreeing with you, only you didn’t realise it.

    [edit]

    you think you are the only person in the entire world that is right, and that everyone else needs to be put in their place.

    So, although you believe in AGW, and mostly are on target, please don’t take it personally if I say (along with most readers here, I think):

    [edit]

  16. 166
    Dan Hover says:

    i love my nasa giss i love my nasa giss
    2005 is getting warmer and warmer, hansen is going crazy and you idiots
    try to find global warming with methods, i can only LOL

    YOU ARE SIK!

  17. 167
    Ray Ladbury says:

    Dan Hover,
    Off the meds again, huh?

  18. 168
    Ray Ladbury says:

    Jim Steele, By “natural variabliity” we mean the energy sources and sinks that influence global temperatures but tend not to result in a long-term trend. Volcanic eruptions, ENSO, PDO, NAO, the solar cycle, etc are examples. Volcanic eruptions occur at random, but rarely, and so can be modeled as a Poisson process occurring at some mean rate. As long as the mean doesn’t change, they don’t induce a long term trend. Other processes may affect cloud cover or the amount of heat going into the deep oceans. However, these processes donot continue indefinitely, and so over long time scales they don’t affect climate.

    In contrast, an increase in greenhouse gasses will over time push temperatures higher as the climate works toward a new state of radiative equilibrium. Hope that helps.

  19. 169
  20. 170

    Paul Clark #163: the forcings are here:

    http://data.giss.nasa.gov/modelforce/RadF.txt

    Column 8 “StratAer”. Don’t know how you could put these on WoodForTrees. Perhaps by downloading their software.

  21. 171
    Hank Roberts says:

    Jim Steele — dhogaza’s pointer to SkepticalScience is a much better answer than mine. That ought to be very helpful to you.

    One other thought — If your questions arise based on something that you have been reading elsewhere, please tell us your source or sources for your puzzles.

    Having a pointer can avoid a whole lot of recreational typing on everyone’s part if you’re reading something somewhere else and trying to check it out.

  22. 172
    Mark says:

    “Re #162 Mark.

    I’m not a denialist.

    You don’t need to put me down.”

    CTG, I don’t put people down for being a denialist. I put people down for [edit] their arguments.

    Now, almost all denialist arguments are idiotic, however, don’t let that make you think that that is the criterion.

    You [edit]

    [no more of this inflammatory stuff from either side, please. -editor]

  23. 173
    Mark says:

    Jim: “For example southern hemisphere ice has been significantly increasing the past years ”

    No, the extent of sea ice has increased.

    Sea ice extent increase != sea ice increase

    Please try again.

  24. 174
    Hugh Laue says:

    Nice articles by Joseph Romm and Gavin in October issue of Physics World that is being offered as a sample copy for free download http://physicsworld.com/cws/download/oct2009
    Clever titles “Publicize or Persih” and “Wrong but Useful” respectively.

  25. 175
    Paul Clark says:

    Martin Vermeer @ 169: Thanks for the link to the forcing data; I could easily add these (most sources are tabular files like this), but I’m not sure they are quite what I’m looking for, because this is model output rather than raw data. It would be an interesting addition to add model outputs but I’m not quite sure I’m ready for that yet… Presumably the GISS forcing model must have taken some raw data about vulcanology (number? total mass ejected?) to create these? If so, where from?

  26. 176
    Howard S. says:

    Mark,
    Despite your self image of superior intelligence I must point out that it’t not too tough to reduce the opposition to “almost all denialist arguments are idiotic” when you make up and/or morph their arguements to sound idiotic.

    As you did with your 134:
    “Scientist says “we may see periods of 10, maybe even 20 years where we get some cooling”
    Populist crap says “an IPCC scientist says we’re looking at 30 years cooling. 40 years. At least”.
    And guess what: when it warms over the next 10 years, it won’t be shown as proof there’s AGW by the populist crap, but as how the IPCC scientists got it wrong again.”

    I follow both sides of this debate and have never seen this denialist claim by anyone. Where did you find it?

    I suspect you made it up.

    In reality the skeptics case grows in specifics and weight which you are avoiding.
    It would be much more meaningful if you addressed their actual arguments instead of your own versions.

    You see there are many people who can tell the difference.
    Who do you think you are fooling?

    You could easily select and quote a specific skeptics argument to refute.

    In the RC camp you are the number one advocate. IMO

  27. 177
    Rod B says:

    Jim Eager (148), saying “we began burning fossil carbon fuels on an industrial scale in 1750″ is quite a stretch. While that is when the first coal was mined in the U.S. industrial scale use came almost 100 years later.

  28. 178
    Jim Steele says:

    Ray Ladbury, That was a clear explanation, and I basically understand exactly what you are saying. However the point I was asking more specifically was about heat input or release or redistribution of heat. Too often I read “natural variability” as a vague catch all that is thrown around to explain every change.

    I think there is a great need to distinguish “variability” caused by “heat redistribution processes” like ENSO vs changes in input and release such as the sun or green house gases. It seems that the distinction is currently based on the fact that CO2 is steadily climbing and other events are more “random” around a mean. But that seems dangerously overly simplistic to have predictive value.

    I think of ENSO as simply redistributing heat from the ocean to the atmosphere. That oscillation around a mean would have no effect on trends because it does not significantly impact the heat balance. However If variability is due to input, ie the sun, then the observed drop in solar activity, magnetism, and sunspots which is now approaching multi-century lows is changing our calculation of the mean. If this change in solar input is similar to other historic changes, then we may approach a new mean or set point similar to that seen in the early 1800’s of the Dalton minimum or 1600’s of the Maunder minimum. If the the heat content is lowered (using OHC as the best metric) then the trapping of heat by greenhouse gases would continue but at this lower set point.

    Also conversely that suggests the solar input during the 1900’s was above the mean. So if the sun input is reverting to a lower mean then it suggests a cooling trend is in store and we might not see the high average temperature’s of the 90’s or 2000’s for another hundred years. Would that still be called natural variability?

  29. 179
    Rod B says:

    PS doesn’t significantly alter your basic point, though…

  30. 180
    Jim Steele says:

    Mark #172 “Please try again.” ??? I can’t decipher the meaning of your reply!

  31. 181
    Jim Prall says:

    Minor nitpick:

    Back at post #24, the name of the first author got the footnote letter appended: it should be Swanson, not “Swansona”

    Great post, and good discussion thread too. Thanks everybody!

  32. 182
    Rod B says:

    Mark (172), isn’t sea ice extent highly proportional/related to sea ice (volume). Like “extent” is partially defined by concentration. Though, maybe concentration is only loosely correlated to volume??

  33. 183
    Hank Roberts says:

    Jim Steele, please tell us where you are reading or hearing the information you are quoting (we assume you didn’t go there yourself and do your own study).

    Once you say where you are getting what you believe, it will be much easier to help you go from that to the underlying science. If the source you are reading does not cite to the science papers, I suggest you look for a better source. Lots of people are pushing opinions based on other people’s opinions.

    Look at the definitions at the sea ice science sites for thickness, extent, and area covered. You know where to look? That should help make this clearer.

  34. 184
    Mark says:

    “Mark (172), isn’t sea ice extent highly proportional/related to sea ice (volume). ”

    Nope.

    The knob of butter on my knife is only a couple of grammes.

    Yet after I spread it on my bread it now occupies a greater surface area than the 500g tub of it.

  35. 185
    Mark says:

    “that oscillation around a mean would have no effect on trends because it does not significantly impact the heat balance. ”

    It does change the trends, though, if you pick your points of reference poorly.

    And even then, it DOES make a small difference: a cold ocean radiates less heat out, so the heat balance is “more in”.

    “Also conversely that suggests the solar input during the 1900’s was above the mean.”

    Period of that being…?

    “So if the sun input is reverting to a lower mean then it suggests a cooling trend is in store and we might not see the high average temperature’s of the 90’s or 2000’s for another hundred years.”

    Check up “begging the question”.

    The answer however is “no”. Because the warming from CO2 is bigger than the variation we see in the solar constant from the sun at a defined distance.

  36. 186
    Mark says:

    “Despite your self image of superior intelligence”

    Superior to some.

    But that’s a consequence of “we are not all alike”.

    So please get on to the point.

    “I follow both sides of this debate and have never seen this denialist claim by anyone. Where did you find it?”

    In the link I gave to the most recent Greenman Crock of the Week.

    Link given.

    That you missed this and made such a song-and-dance about it is WHY I deem [edit]

    http://www.youtube.com/watch?v=khikoh3sJg8

    Watch it. It’s in there.

    [edit-lets watch the inflammatory comments. we’ll discontinue this thread if you guys can’t keep it civil and on topic]

  37. 187
    Mark says:

    ” Jim Steele says:
    8 October 2009 at 10:37 AM

    Mark #172 “Please try again.” ??? I can’t decipher the meaning of your reply!”

    Please try again: your evidence is not evidence of there being more ice.

  38. 188
    Nefastus says:

    Rod B says:
    8 October 2009 at 11:03 AM
    Mark (172), isn’t sea ice extent highly proportional/related to sea ice (volume). Like “extent” is partially defined by concentration. Though, maybe concentration is only loosely correlated to volume??

    No.
    It is not the same.
    Extent is not partially defined by concentration.
    Concentration is not correlated to volume.

  39. 189
    Mark says:

    My point is that if you’re smart but don’t use it, [edit]

    And bad arguments are [edit]

    [edit]

    A good argument well made, even if wrong, remains a good argument and helps learning.

    A bad argument, or a good one poorly one, even if right doesn’t.

    [editor-ok, that’s enough of this particular thread]

  40. 190
    Krog says:

    113.#79 Krog

    My interpretation based on your answer is that you don’t care about learning the answer to your questions… So why did you ask? Is it that:

    1. You like to ask questions you don’t want answers for?
    2. You are ignoring the facts?
    3. You like disrupting the thread?
    4. You like wasting peoples time?
    5. You are inconsiderate?
    6. You like seeing your words online?
    7. You are bored and have nothing better to do?

    You should read page for of the IPCC report as suggested. It’s only one page (actually about two paragraphs and a graphic with a description). But I guess two paragraphs are a bit much to ask you to read. Are you opposed to educating yourself and science?

    To compare ‘a page’ in a report to War and Peace… Hmmm… How moronic.

    BTW The answer is more simple than you think. Just add up the positive and negative numbers and their ranges that are contained in the two paragraphs.

    Or am I grossly misinterpreting that which you apparently infer/state in your post?

    Comment by John P. Reisman (OSS Foundation) — 7 October 2009 @ 7:59 AM
    Only #6 is correct.
    I meant no offense.
    I thought that my ? would get a simple answer.
    The idea of heat content being a more meaningfull metric than temp was brought up by another poster. It made sense to me.
    I clicked to the IPCC site, was overwhelmed. Not a scientist, don’t have time to research the answer to my dumb questions.
    I learned that even simple questions have complicated answers.
    Was attempting humor, yes you may have “grossly misinterpreted” my post.
    Krog

  41. 191
    Rod B says:

    Mark, but if a couple of grams of butter melted and spread on its own (lets assume on a non-absorbing surface), wouldn’t its extent be far less than 500 grams doing the same thing?

  42. 192
    Rod B says:

    Nefastus (188), the Colo ice monitoring site defines “extent” as sea H2O where the ice concentration exceeds 15%. …as near as I understand it. Is this wrong? Or am I interpreting it incorrectly?

  43. 193
    colin Aldridge says:

    The evidence I have seen from DMI doesn’t suggest any warming over the last ten years.. it shows arctic tempreatures more or less at the 1958 – 2008 mean apart from 2007 and 2008. Wher do they get their temperature data from? Anybody know?

  44. 194
    Martin Vermeer says:

    Paul Clark #175: would that be http://data.giss.nasa.gov/modelforce/strataer/ ?
    Found by backtracking from tamino to GISS data file to GISS documentation… a useful skill to acquire ;-)

  45. 195
    Patrick 027 says:

    Re Jim Steele 178, 180 (aside from others’ responses) –

    There might be a conflation between natural variability and internal variability. Internal variability is a subset of natural variability. The other part of natural variability is forced variability. Obviously, if there is/were a significant unreversed change in natural forcings (which can be in the form of a change in temporal averages), the climatic response to that will be tend to be something more than fluctuation about a the same constant mean (if the time scales of positive and negative feedbacks are different in the right way, though, a sharp change in forcing could cause a large initial change that then decays with time – for example, ice sheet growth following continental drift, then followed by CO2 increase due to reduced chemical weathering (very long timescales, there)).

    Internal variability is unforced variability. Some form(s?) are approximately like internal clocks – for example, the QBO, which is a quasi-cyclical reversal of winds in the equatorial stratosphere that is caused by processes (vertical propagation of equatorial Rossby-gravity and Kelvin waves, etc, followed by wind-shear selected absorption of wave momentum fluxes.) that are not organized by any cause with such a periodicity. Other forms are more irregular (ENSO, NAM and SAM, sudden stratospheric warmings, shorter term weather). Consider small-scale vertical convection – radiative forcing tends to reduce static stability; sufficient perturbations can force lifting to the point where latent heating powers the updrafts. This is highly episodic over small time intervals but tends to approach an average rate as determined by energy supply, etc. ENSO variability is an example where a sea surface temperature anomaly drives or reinforces atmospheric circulation change (via latent heat releases) which itself can reinforce the sea surface temperature anomaly. It is also possible for redistributions of momentum (wind) to be self-reinforcing by shaping the momentum transports by waves/eddies. Droughts tend to sustain themselves. But even where longevity is not inherently finite to the subcomponent of the system, external perturbations (from other parts of the system) (which can be expected to come along with some probability distribution in time) can knock the weather patterns out of these conditions just as they can initiate them – if they can’t, then the climate would sooner or later settle into such a state for the long term and so it would no longer be a form of internal variability.

  46. 196
    Martin Vermeer says:

    Jim Steele #178: the distinction you’re after is between unforced and forced natural variability.
    Unforced NV looks random, sort-of, but is the result of the chaotic nature of the climate system; deterministic in principle, but ill-predictable. Some of it has a name, like el Nino; much of it has not. We have a pretty good idea how much variance there is here; this is the “real” NV that explains why model runs differ from each other and from the real world, and why temps don’t climb from year to year even if forcings do.
    Forced NV is greenhouse gasses, solar, Milankovich, etc. Fully deterministic and a very mixed bag.
    BTW I don’t think you’re being quite realistic about the kind of effect a quiet Sun could produce. The numbers I’ve seen are a few tenths of a degree max, meaning at best a postponement of the ongoing warming (at 0.2 degrees/decade!), hardly cooling.

  47. 197
    RichardC says:

    191 Rod asks, ” if a couple of grams of butter melted and spread on its own (lets assume on a non-absorbing surface), wouldn’t its extent be far less than 500 grams doing the same thing?”

    Not if the “butter” (ice) is constrained to a “bowl” (the arctic basin). Then, the volume will drop tremendously before the extent changes much at all.

  48. 198
    Hank Roberts says:

    > if a couple of grams of butter melted and spread on its own
    > (lets assume on a non-absorbing surface)….

    Analogy FAIL

    Sea ice — water ice. Open water can produce more sea ice. Solid ice can split up and blow around and make more open water.

  49. 199

    Lets have fun with the skeptical argument, otherwise all people of reason would despair at the waste of time spent to deal with it!

    THe Northeast passage appears still open!

    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/arctic.jpg

    for the Cryosphere today critics:

    http://manati.orbit.nesdis.noaa.gov/ice_image21/D09280.NHEAVEH.GIF

    this to compared with the skeptics favorite year:

    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/ARCHIVE/19981008.png

    See a resemblance? Are you satisfied of the cooling effect over the Polar ice cap?

    HAHA do you want me entertained further with your comedy?

  50. 200
    dhogaza says:

    Mark, but if a couple of grams of butter melted and spread on its own (lets assume on a non-absorbing surface), wouldn’t its extent be far less than 500 grams doing the same thing?

    But one of the key attributes of sea ice is that it’s not melted …

    And the way sea ice extent is measured by NSIDC and IJIS, just over 15% coverage by thin ice counts the same as if it were 100% covered by thick multiyear ice.


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