Technical Note: Sorry for any recent performance issues. We are working on it.
To our readers who have followed the supposed ‘hockey stick controversy’, this press release from NCAR just out today, will be of interest.
Vindication! Great to hear! (Now let’s hope some policymakers take this message to heart.)
Never make a claim until the other side is heard from. Peculiar that this is announced / posted here just when M&M are before the public. Since this material is supposed to have been presented back in December, why hasn’t it been discussed here before?
[Response: Back in December there was an just a conference abstract of the work; now it is a submitted paper.-eric]
More details at http://tinyurl.com/82veh
Not that you really needed it but it is good that your analysis is confirmed. The sad fact is that GW skeptics have very successfully used this false controversy to generate much doubt in the minds of the public. It will take time to counter this.
It is good to see this post. Realclimate is doing a great job popularizing climate change science, but this is no easy task. We need the facts and RC is giving us them.
Stephen Gloor unfortunately is right. The skeptic spin machine has been successful using this false controversy to generate doubt. I was reading a national environmental group’s blog earlier. Environmentalists who desperately want to take action to control global warming have heard the things the skeptics are saying and these same environmentalists are making comments supporting what the skeptics are saying!
In re #2 the timing of this announcement by climate scientists could be suspicious. It is a little known fact that “conspiracy and plotting” is a required class in climatology school.
I love this from the link given by caerbannog (#3 above):
“In Summary, it can be clearly stated that none of the warm 15th century reconstructions turn out to be statistically and climatologically meaningful. The centering issue raised by McIntyre and McKitrick in GRL (2005a), if approached properly (i.e. using full standardization of individual records), is influencing the reconstruction in a minor way and is in fact confirming the robustness of the MBH reconstruction within its own framework.”
It’s what you guys have been saying all along. How long before the paleontologist Ammann and NCAR are attacked by the carbon industry? I give it a week at most. Hope I’m proved wrong.
Re: #2 “claim until the the other side is heard from…”
What other side? There is no controversy at all about the Hockey Stick and there never has been. In fact, I wonder if you (Dave Dardinger) are a “plant” from the skeptics to try to sow confusion here at RC.
[Response: Dave, please note that people's comments are assessed based solely on the content, rather than from 'where they come from'. We are trying to keep the discussion here focused on the issues. In this particular case, one could argue that the controversy was mis-informed, but I don't think you could argue that there wasn't a conroversy at all! - gavin]
This is a great day.
Re #5: Joseph, could you give me a link to that discussion? I’m *very* curious.
Re #2: I absolutely applaud this sort of “laying in wait,” if that’s what it is. MM should never be mentioned without reference to their stupendous error in substituting radian for degrees in their GRL paper, nor to the mass resignation of editors protesting the publication of that paper. Apparently the National Press Club has no standards whatsoever.
Correction to my last post: The radians/degrees problem and the mass resignation were at Climate Research, not GRL, and that particular particular paper was McKittrick and Michaels.
Sorry, yet another correction: The mass resignation was in response to publication of a prior paper disputing anthropogenic global warming, although the editor of this latter paper was the same as with MMichaels. There, I think I’ve got it striaght.
Re #6, sadly I’m sure the sceptics will make a great fuss about the fact that Ammann is a contributor to this website. Doubtless he will be painted as part of an evil circle of conspirators who are in this for the research grants and because they hate America or something.
OK, Gavin, I regret that comment. Here’s what I should have said.
Having read all of Mike’s posts on the subject, the only legitimate peer-reviewd paper mentioned (Here) is Von Storch et. al. So, I can’t argue that there is no controversy at all. So far, there has been no post on that work.
Outside of this lone exception, the dispute has involved people who are not climate scientists whose flawed work slipped through a sloppy peer-review process (as discussed in False Claims by McIntyre and McKitrick) and elsewhere on this site, or highly qualified people like Michael Crichton. For some history on all this, see the Contrarians page at Stephen Schneider’s website.
I repeat this material, which is familiar to readers of RC, because new people come online here all the time. If they read about not making claims until the other side is heard from, they should know what the “other side” amounts to.
The techniques used by climate science “skeptics” to cast doubt are clear. The strategy is explcitly put forward in this memo by political advisor Frank Luntz (as quoted in Elizabeth Kolbert’s “The Climate of Man (Part III)” – New Yorker, May 9, 2005.
The scientific debate is closing (against us) but not yet closed. There is still a window of opportunity to challenge the science…. Voters believe that there is no consensus about global warming in the scientific community. Should the public come to believe that the scientific issues are settled, their views about global warming will change accordingly. … The most important principle in any discussion of global warming is your commitment to sound science”.
This last phrase “sound science” is the current buzzword used by Paula Dobriansky and others in the current administration. Its use implies that the science is somehow not sound. In this case, many studies (“the Hockey Team”) outside of Mann et. al. 1998 have come to the same conclusions about the climate of the last 1000 years and the current anomaly. Put against this is one paper by Von Storch et. al. and the McIntyre and McKitrick paper.
So, when I see posts like #2, I am reminded that there is a concerted campaign being waged here in the United States to disseminate doubt about valid climate science results. I have no idea what Mr. Dardinger’s motivation is, perhaps he has simply internalized doubts that were cast by others or, as in many cases, is unwilling to believe the bad news that climate science brings. In any case, that comment creates doubt where in fact there is not a lot of controversy in the consensus view based on the best science available.
jaime beaucoup ce que parle votre blogue mais encoe plus que vous le mettiez en francais
Your response # 13 is somewhat better stated, but still misses the point. Science is a process of give and take as theories and data are presented and then rebutted. Ammann has presented (or submitted at least) his findings, but there has been no peer review, no paper released and no chance for M&M to respond yet. I was careful when the original M&M findings were announced to state on the forum I normally hang out on that I was withholding final judgement until their work was published & others had been heard from. Up till this point, their findings of methodological flaws in the original Mann paper have been upheld. This upcoming paper denies these flaws, as far as I can see, but until the paper itself is released and until M&M have had a chance to respond, it’s rather early to declare the second coming of Mann has arrived.
Due to the bizarre redirect, my published Stephen Schneider link will not work. Here’s a correction.
Also, I am pleased to announce that McIntyre and McKitrick spoke yesterday at the National Press Club in an event sponsored by the Cooler Heads Coalition and the Marshall Institute ($310,000 in funding from ExxonMobil from 2000 to 2003 – use the “event” link). The talk was titled “Hockey Stick or Slapstick?”. Regretfully, I was unable to attend but my favorite quote from the announcement is:
The authors of the original hockey stick papers and their allies initially conducted a furious counter-attack to defend their work and question the competence and motives of their critics. Recently, they have shifted their ground to claim that the hockey stick is an irrelevant distraction because there is a wealth of other evidence supporting their views.
Perhaps this refers to What If the Hockey Stick Were Wrong? posted here by Stefan. And of course I’ve read that Mike has or is going to “shift his ground” from Virgina to Pennsylvania. He’s on the run!
Re #9: To be fair to the National Press Club, it looks to me like they may have simply been renting out their conference rooms to the conservative think-tank George C. Marshall Institute (and Cooler Heads Coalition) for the presentation and may have not had any editorial control over the content of what was presented there. At least, I hope that is the case.
Re #15: “Up till this point, their findings of methodological flaws in the original Mann paper have been upheld.” Upheld by who exactly? All the information I’ve seen outside of those in the “skeptic community” (who tend in their own turn to be a bit thin on peer review) has been to the contrary. Anyway, here’s a link to the Tim Lambert’s blog page with more than anyone really needs to know about every one of McKitrick’s massive and apparently ongoing errors: http://cgi.cse.unsw.edu.au/~lambert/cgi-bin/blog/science/McKitrick/.
“Hocky Stick” graph vindicated.
The hockystick graph that has been widely identified as the symbol of Global Warming, has been reproduced by NCAR or National Center for Atmospheric Research using their own homebrew code
. This being a U.S. agency and all, its hard for anyone to cry …
This is extremely interesting, but shouldn’t we wait until the paper makes it past peer review before lauding its praises?
The New Yorker articles mentioned can be read by backtracking from here:
I’m new to all this, so maybe you can answer some newbie questions.
1. Why does the hockey stick use the surface temperature record for its most recent data and not the satelite data?
[Response:Because the overlap between the proxy records (many of which only go up to 1980) and the satellite record which starts in 1979, is too short. Plus the satellite record is not measuring surface air temperature which is the key variable that people are trying to reconstruct. -gavin]
2. Why doesn’t the hockey stick use tree-ring data to estimate the most recent temperature trend? What would it look like if it did?
[Response:Over the recent period, all the proxies (including tree rings) are calibrated to the recent data, and so it looks the same. ]
Another newbie question:
I was just noticing the scale on the vertical axis of the hockey stick. It shows variation of about 0.4 degrees over a 1,000 year period (for the smoothed series). How does this compare to long term temperature variation since the ice age? How much have temperatures changed since the last ice age? Over how long a period did it change? Is the temperature over the last 1,000 years unusually stable?
[Response: The global temperature change at the peak of the last ice age (about 20,000 years ago) were about 5 to 7 deg C colder than the present. Most of that seems to have warmed up by around 11,000 years ago, at which point temperatures in the mid to high latitude Northern Hemisphere were actually warmer (because of the orbital configuration). However, truly global estimates of the mean temperatures through the Holocene is extremely difficult and has only really been attempted for last couple of millennia. -gavin]
I am a bit confused by Gavin’s responses to #22.
I thought all of the prehistorical temperature reconstructions were plotted with “temperature anomalies” on the y-axis. Since all of the proxy sources are located at different latitudes and elevations and therefore have different ambient temperature conditions, this is the only way they can be compiled.
If the temperature anomalies for the individual proxy sites can be compiled this way, why can’t they be compared to the temperature anomaly data from any of the MSU data sets. Given that the absorption of IR energy in the troposphere and subsequent surface warming resulting from reduced heat transfer from the surface is supposed to be what’s driving surface global warming I would have thought that seeing this clearly presented would be important.
I was also under the impression that the IPCC had concluded that the global warming recorded in the first half of the 20th century was mostly “natural” and the warming observed in the second half of the 20th century (starting in 1975) was mostly “anthropogenic”. If this is true then this means the proxy record should only be able to show the anthropogenic warming between 1975 and 1980.
When I look at the Wikipedia “Image:1000 Year Temperature Comparison” it looks like all the proxy reconstructions show more warming in the first half of the 20th century than the second half of the 20th century. Shouldn’t it be a priority to update the major proxy records to the end 20th century to clearly demonstrate the anthropogenic impact?
[Response: You are correct. It is the anomaly temperature that is calibrated against. However, it does not matter which satellite record you are looking at, none of them are the surface air temperature (lower tropopshere is not the same thing), and you still have an overlap problem. You can even argue that the 100+ years of instrumental record are still not sufficient to calibrate the proxies for multidecadal and longer variability, the relatively few years available from the satellites (which of course have calibration issues themselves) is not going to help. Updating the proxy networks to the present day would of course be helpful, as would adding to the number of long (multi-centennial) records. -gavin]
I am a little bit confused by all the triumphalism, and I can’t see what the fuss is about.
The results that Wahl & Ammann get are just about identical to those reported by M&M; indeed, their major conclusion that omission of the Bristlecone pines leads to the 15th century temperature statistics lacking significance has also been noted by M&M.
Given that their results are so very similar to M&M, why all the hoo-haa ?
[Response: Not sure what you are referring to that we have said, but the reason why this is noteworthy is because it underlines our comments made earlier that the PC normalisation issue that was the basis for the M&M (2005) paper is irrelevant, and that the reconstructions only diverge (and get worse) if you start removing data. Thus the argument can move on from the methodology of MBH98 to more important issues. - gavin]
Wow. There was a lot of variation in temperatures over the past 20,000 years. A change of 5 to 6 degrees over 9,000 years is about 0.6 degrees per thousand years. You imply that there have been significant temperature swings since then also.
By contrast the hockey stick shows virtually no change over 1,000 years in the mean temperature and only a small variation in temperature over the past 1,000 years (+- 0.2 degrees variation from the mean) (ignoring the recent uptick in temperatures). Does this recent stability sound at all suspicious to you? A priori, wouldn’t you expect to see temperature swings more along the lines of Espers, Wahl & Ammann, and M&M, Soon and Baliunus etc.? To put it differently, which is more likely, that temperatures were unusually stable over the past 1,000 years or that the hockey stick is generated by a weak model unable to detect significant temperature swings from the tree-ring record?
To strenghten your case, you should address this frontally. After all, it is the heart of the debate, i.e., is a recent rise in temperatures of about 0.5 degrees so unusual that it must be anthropocentric? If different models give different results, which should we believe? It would help tremendously if you could show or at least explain why we should choose the model that produces highly stable temperatures over the ones that show significant fluctuations. Moreover, it would help if you could show why we should expect this temperature stability to continue into the future.
As I mentioned in another message, the most powerful argument you could make would be to calibrate your model from data that doesn’t include the recent warming and show that it can predict the recent warming. That should be easy to execute. That would show that your model has the power to predict large temperature swings. Since your model shows recent temperaturs to be far above anything seen in the last 1,000 years, the recent tree-ring record must be completely off the charts. Every year, we should be seeing observations never before seen in the 1,000 year tree-ring history. You should be able to see this in the data with the naked eye.
A couple of quick analyses should solve this question once and for all. Do it! Let’s prove that humans are causing this warming!
[Response:There seem to be a lot of misunderstandings in the above. The last 20 kyr includes the end of the last ice age, which was indeed a large change, but as you note, rather slow. It also includes large swings - D-O type stuff - within the last ice age. Those don't appear in any record from since the end of the ice age - ie, the holocene. You say, A priori, wouldn't you expect to see temperature swings, to which the answer is, No, why should you expect this a priori? You have to go by what the records show. Which is, that the holocene has indeed been an "unusually" stable period. You seem to be a bit confused about the reconstructions. W+A largely reproduce MBH; S+B don't have a reconstuction; neither, technically, do M&M. The swings in the Esper record are larger than the MBH version, but still show now to be unusually warm, and the recent warming to be unusually fast. And... this is only one small component of D+A - William]
Ice core records suggest the idea of Holocene stability (8.2ka even aside) but this notion is somewhat mythical. There are plenty of records, particularly from low latitudes that demonstrate rapid (and reasonably large scale, big enough to cause significant ecosystem responses) climate changes during the Holocene.
However, its a fallacy to suggest that just because temperatures have changed in the past we can’t be responsible for temperature changes now. Furthermore, the fact that climate changes in the Americas and the Middle East during the Holocene appear to have aided the decline of civilisations is an important cautionary tale.
While it is true the decline of cultures/civilizations is associated with climate change these declines are generally associated with periods of cooling.
I am not aware of a culture/civilization that declined as climate warmed. There are numerous examples of cultures/civilizations thriving during warmer periods.
I am not aware of any civilizations that did not occur during the Holocene.
Regarding post #28: “I am not aware of a culture/civilization that declined as climate warmed”
First, there is very little in the way of archaeological data about cvilzations during the transition from the last glaciation to the Holocene. There is therefore no record of any civilation disappearing for any clearly known reason. So the statement proves nothing.
Since sea surfaces rose by roughly 400 feet since the peak of the last ice age due to melting of glaciers, it is quite possible that a great many civilizations did decline or perish due to warming, and in fact perished so thoroughly that there is no trace of them. It is also possible that the sea level rise was gradual enough that the impact was mitigated on low-population hunter-gatherer societies that simply moved to higher ground. Unfortunately, New York, London and Tokyo are not low-population hunter-gatherer communities that can be easily uprooted. I’m not an economist, but I would have to guess that cost of moving all of the world’s modern cities that are close to sea-level to higher ground would be rather significant.
I remain unaware of any culture/civilization that declined as climate warmed.
There are numerous examples of cities that have had to deal with rising or lowering sea levels. To my knowledge none of these resulted in the decline of a culture/civilization. Current examples include Venice and New Orleans.
A great read on the topic is “The Long Summer” by Brian Fagan. He tells the story of how civilisation is impacted by climate.
Oh, and if climate change continues unchecked, sea levels will rise enough to devour Venice and New Orleans, not to mention Rio de Janeiro, Shanghai, and many hundreds of other cities that are located on coastlines at low elevations. Millions of people will have to relocate, leaving behind their livelihoods and dreams, which will cause the greatest refugee crisis the world has ever seen. I hate to sound the doomsday alarm, but the Pentagon also mentioned this in their report.
http://www.ems.org/climate/exec_pentagon_climatechange.pdf (The executive summary)
http://www.ems.org/climate/pentagon_climatechange.pdf (The full report)
Re #28: Try the Anasazi. Strictly speaking, it was the lack of rainfall that did them in, but this was during the medieval warm period. Even subtle changes in climate (hotter or colder) seem able to change rainfall patterns in ways that are very bad for human societies, in particular those in already-marginal climates.
Recently I was talking with a water manager for a local district here in the SF Bay Area, and he told that sediment records in Lake Tenaya (roughly in the middle of the western slopes of the Sierra Nevada mountains) showed a multi-year period in the 1200s with no sedimentation whatsoever, meaning essentially no precipitation. This was part of the same drought that got the Anasazi. A repeat of this entirely natural event would be a large-scale catastrophe for the western U.S., to say the least. Two years of such a complete drought would largely eliminate all natural water supplies for a population in the 50M range. Now let’s see, what can we humans do to bring on another such event as soon as possible?
Speaking of California, the geologic record proves that we get great earthquakes once every 200 years or so on the major fault sections, and are close to overdue at this point. The fact that public policy in CA continues to be directed toward packing as many humans as possible onto the major fault zones speaks for itself, and does not augur well with regard to our ability as a society to deal coherently with climate change.
Re #30, Ahhh, so you admit it’s warming then Jeff, you just don’t see it as a problem ;) That’s progress of a sort :)
Re The Holocene, surely it’s a time where global temperatures show no sign, until now, of (excluding the rise out of the ice age before that’s the cry) temperatures rising. Indeed the opposite seems to be the case, if my memory of the appropriate wiki page(s) serves me correctly. So, it’s unlikely any civilisations have faced problems associated with rising temperatures – until now.
Actually, civilization ‘collapse’ in the Holocene is often related to changes in precipitation (to more arid conditions) rather than temperature:
Hodell, D.A., Curtis, J.H. and Brenner, M. (1995) Possible role of climate in the collapse of classic Maya civilization. Nature, 375, 391-394.
Cullen, H.M., deMenocal, P.B., Hemming. S., Hemming. G., Brown, F.H., Guilderson, T. and Sirocko, F. (2000) Climate change and the collapse of the Akkadian empire: Evidence from the deep sea. Geology, 28, 379-382.
Huang, C.C., Zhao, S.C., Pang, J.L., Zhou, Q.Y., Chen, S., Li, P.H., Mao, L.J. and Ding, M. (2003) Climatic aridity and the relocations of the Zhou culture in the southern Loess Plateau of China. Cliamtic Change, 61, 361-378.
Anyway, the point I was making seems to have been missed in post #28, namely (and simply) that significant climate changes can have adverse effects on human populations. Furthermore, given that ‘global warming’ doesn’t mean that the whole world is simply going to get warmer (rather, climate changes will be complex), pointing out that civilizations in the past may not have been affected by warming is something of a red herring.
Re #9 Steve Bloom the environmental group blog I refered to is the NRDC’s actionblog. Some of the comments (from commentors but not from the NRDC) that support the skeptic’s claims about the hockey stick and Dr Mann are here:
A book that discusses climate change effects on human history is “Climate History and the Modern World” by Hubert Lamb. It’s not too technical and it’s a good summary of this topic.
So there was a medieval warm period and it did have climate impacts outside of Europe and the North Atlantic. I thought so.
Global temperatures increased during the 20th century. I have never doubted this. Perhaps you are confusing me with someone else.
If as Steve says there was a global medieval warm period, there must have been a time before that when it was less warm (there was). Therefore there must have been a period just prior to the medieval warm period when global temperatures increased.
I hope this helps with your progress.
Re#29: “There are numerous examples of cities that have had to deal with rising or lowering sea levels…Current examples include Venice and New Orleans”
You’re oversimplifying here – these are notable but IMHO poor examples. The underlying problem with these places is not sea level rise but poor location and engineering. It’s akin to building your house next to a dump and then complaining that it smells when the trash haulers dump their loads.
Venice’s major problem is subsidence, some of it due to pumping of water from underground aquifers, some of it due to development, and some of it “natural.” The MSL rise in the 20th century around Venice was measured to be 3 inches, while the mean subsidence of the land was measured to be twice that at 6 inches.
The problem with New Orleans is that most of it is below sea level – by as much as 6 feet. They have to pump out stormwater as it is. Developing marshland has just worsened the problem.
Coastal and floodprone areas will always have issues, regardless of global temps. Even when the global temps were cooler than today, Galveston, TX was practically wiped off the map by a hurricane in 1900. Prior to that, it was the booming fourth largest city in TX and the state’s main shipping port. It was also the financial center of TX and the world’s largest port for cotton. After that disaster, it was Houston with it’s shipping channel that took over while Galveston rebuilt, and the rest is history.
“You’re oversimplifying here – these are notable but IMHO poor examples. The underlying problem with these places is not sea level rise but poor location and engineering. It’s akin to building your house next to a dump and then complaining that it smells when the trash haulers dump their loads.”
This is a silly thing to say, since these cities were created before the world had to worry about rising sea levels being a result of human-caused global warming. Venice especially, since it was created millennia ago.
These were created as strategic port cities where merchants and tradesmen could buy and sell goods with ease and make it back home before too long. Had they had to go to, say, Kansas City or Minneapolis via the Mississippi (and over land a bit, too) instead of New Orleans, it would have taken them weeks longer, which would have really strained their resources and been far more dangerous, especially with the high prevalence of disease on these missions back in those days.
Back when these cities were created, there was no trash to be thrown out yet and the dump was only a pipe dream.
There is a reason that every city, town, village, subdivision, neighborhood, and home is built where it is. Venice and New Orleans are no exception – there are reasons they exist and grew. But the bad has to be taken with the good, as it has all along.
If you believe Nova http://www.pbs.org/wgbh/nova/venice/sieg_nf.html , the pumping of water from an aquifer underneath Venice from 1920-1970 is reportedly responsible for 4.5 inches of subsidence alone – 150% of the MSL rise of the 20th century. In other words, the location and engineering of those 50 yrs accelerated Venice’s flooding problems by well over a century. The fault of Venice’s founders? No. But it is still a consequence of the location and the surrounding geology particular to Venice.
Check out the wording in the first item #6 on the Nova link: “…In the 1600s, normal tides seldom rose over the stone footings at the base of buildings…” How many cities do you know of where “normal tides” EVER rise over footings? Note also that crude sea walls were built in the 1400s and again through the 1800s – clearly there was at least some issue with the location long ago. Once again, the bad was/is taken with the good.
Nobody is faulting people for settling and developing those cities. But they still always were and always will be problematic locations.
Check the comments above. Sea levels have been risen 400 feet since the end of the ice age. They will continue to rise regardless of whether we attempt to do anything about recent warming. The increase has been and will continue to be very slow and humans will adapt to it as they have for the past thousand years.
If you accept there was a Medieval Warm Period, then you accept that the hockey stick is wrong — it can’t detect it.
[Response:This is the sort of comment that we will typically screen out, because it increases the 'noise' relative to the 'signal' in the discussion. Even a cursory reading of our various previous posts, including our discussion of the Medieval Warm Period here , exposes the ignorance underlying this sort of statement]
BTW. I can’t think of any (reasonable) person that doesn’t believe the climate has warmed in the past hundred years and that it will (or may) continue to do so. The (seriously) debated questions are: what is the rate of increase, how sure are we that it will increase, can anything be done about it, and will it be beneficial or harmful. (BTW, it is undisputed (by serious people) that there will be many beneficial effects … the question is, do the negative effects outweight the positive ones.)
“The (seriously) debated questions are: what is the rate of increase, how sure are we that it will increase, can anything be done about it, and will it be beneficial or harmful. (BTW, it is undisputed (by serious people) that there will be many beneficial effects … the question is, do the negative effects outweight the positive ones.)”
The rate of increase (i.e. change in temperature per year) is increasing, so maybe the best way to tell is by comparing decadal changes.
Sure, things can be done to mitigate the changes (consuming less energy, wasting less, etc.). However, it looks as though there may have been irreparable damage done to the planet and that greenhouse gases will stay anomalously high for decades, even centuries, after we stop emitting greenhouse gases.
As for the effects of global warming, sure there are some that are beneficial. However, the negative effects far outweigh the positive, since the lives of millions of people will be (and perhaps are already) at high risk. The mass destabilisation of millions of people (perhaps up to a half-billion) cannot be outweighed by any benefit (such as the savings of money on heating during harsh winters in North America or expanded shipping routes through the Arctic) since it is people’s lives at stake (not to mention the likely extinction of millions of species of wildlife).
Let me add to Stephen Berg’s comment (42). The beneficial effects of gloabl warming are all on the low side of the warming, the negative effects are concentrated on the high side. As we go higher in global temperature the negative effects grow exponentially (maybe an exaggeration, but not much).
The high end of current estimates for climate sensitivity are already in very negative and serious terratory. The bad news is that the risks are seriously asymmetric and we are betting the house. The good news is that we still have a little time to take action without risking experiencing the worst consequences. The bad news is that humans mostly need to have the roof fall in before they start repairs.
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