Study using paleoclimate data suggests climate sensitivity to CO2 doubling may be less severe than projected
25 November 2011
A new study, funded by the National Science Foundation’s Paleoclimate Program and published online this week in the journal Science, suggests that the rate of global warming from doubling of atmospheric carbon dioxide from pre-industrial times may be less than the most extreme estimates of some previous studies and may be less severe than that projected by the Intergovernmental Panel on Climate Change (IPCC) report in 2007.
The team combined extensive sea and land surface temperature reconstructions from the Last Glacial Maximum (LGM) with a climate model of intermediate complexity to estimate the equilibrium climate sensitivity for a doubling of atmospheric carbon dioxide concentrations (ECS2xC) from preindustrial times. (Climate sensitivity is the change in global mean surface air temperature caused by radiative forcing of Earth’s radiative balance at the top of the atmosphere with respect to a given reference state.)
Their results showed an estimated lower median temperature increase (2.3 K) and reduced uncertainty (1.7 to 2.6 K 66% probability). Assuming paleoclimatic constraints apply to the future as predicted by their model, the researchers concluded, their results imply lower probability of imminent extreme climatic change than previously thought.
The experiments collectively favor sensitivities between 1 and 3 K. However, we cannot exclude the possibility that the analysis is sensitive to uncertainties or statistical assumptions not considered here, and the underestimated land/sea contrast in the model, which leads to the difference between land and ocean based estimates of ECS2xC, remains an important caveat.
Our uncertainty analysis is not complete and does not explicitly consider uncertainties in radiative forcing due to ice sheet extent or different vegetation distributions. Our limited model ensemble does not scan the full parameter range, neglecting, for example, possible variations in shortwave radiation due to clouds. Non-linear cloud feedbacks in different complex models make the relation between LGM and 2×CO2 derived climate sensitivity more ambiguous than apparent in our simplified model ensemble. More work, in which these and other uncertainties are considered, will be required for a more complete assessment.
In summary, using a spatially extensive network of paleoclimate observations in combination with a climate model we find that climate sensitivities larger than 6 K are implausible, and that both the most likely value and the uncertainty range are smaller than previously thought. This demonstrates that paleoclimate data provide efficient constraints to reduce the uncertainty of future climate projections.
—Schmittner et al.
The authors emphasize that global warming is real and that increases in atmospheric CO2 will have multiple serious impacts. However, the most extreme projections of temperature increases from the doubling of CO2 are unlikely, according to their work.
Many previous climate sensitivity studies have looked at the past only from 1850 through today, and not fully integrated paleoclimate data, especially on a global scale. When you reconstruct sea and land surface temperatures from the peak of the last Ice Age 21,000 years ago—which is referred to as the Last Glacial Maximum—and compare it with climate model simulations of that period, you get a much different picture.
If these paleoclimatic constraints apply to the future, as predicted by our model, the results imply less probability of extreme climatic change than previously thought.
—Andreas Schmittner, Oregon State University researcher and lead author
Scientists have struggled for years trying to quantify climate sensitivity—how the Earth will respond to projected increases of atmospheric carbon dioxide. The 2007 IPCC report estimated that the air near the surface of the Earth would warm on average by 2 to 4.5 °C with a doubling of atmospheric CO2 from pre-industrial standards. The mean, or expected value increase in the IPCC estimates was 3.0 degrees; most climate model studies use the doubling of CO2 as a basic index.
Some previous studies have calculated the impacts could be much more severe—as much as 10 degrees or higher with a doubling of CO2. Studies based on data going back only to 1850 are affected by large uncertainties in the effects of dust and other small particles in the air that reflect sunlight and can influence clouds, known as “aerosol forcing,” or by the absorption of heat by the oceans, the researchers say.
To lower the degree of uncertainty, Schmittner and his colleagues used a climate model with more data and found that there are constraints that preclude very high levels of climate sensitivity.
The researchers compiled land and ocean surface temperature reconstructions from the Last Glacial Maximum and created a global map of those temperatures. During this time, atmospheric CO2 was about a third less than before the Industrial Revolution, and levels of methane and nitrous oxide were much lower. Because much of the northern latitudes were covered in ice and snow, sea levels were lower, the climate was drier (less precipitation), and there was more dust in the air. All these factors, which contributed to cooling the Earth’s surface, were included in their climate model simulations.
The new data changed the assessment of climate models in many ways, said Schmittner. The researchers’ reconstruction of temperatures has greater spatial coverage and showed less cooling during the Ice Age than most previous studies.
High sensitivity climate models—more than 6 degrees—suggest that the low levels of atmospheric CO2 during the Last Glacial Maximum would result in a runaway effect that would have left the Earth completely ice-covered.
Clearly, that didn’t happen. Though the Earth then was covered by much more ice and snow than it is today, the ice sheets didn’t extend beyond latitudes of about 40 degrees, and the tropics and subtropics were largely ice-free—except at high altitudes. These high-sensitivity models overestimate cooling.
—Andreas Schmittner
On the other hand, models with low climate sensitivity—less than 1.3 degrees—underestimate the cooling almost everywhere at the Last Glacial Maximum, the researchers say. The closest match, with a much lower degree of uncertainty than most other studies, suggests climate sensitivity is about 2.4 degrees.
Reconstructing sea and land surface temperatures from 21,000 years ago is a complex task involving the examination of ices cores, bore holes, fossils of marine and terrestrial organisms, seafloor sediments and other factors. Sediment cores, for example, contain different biological assemblages found in different temperature regimes and can be used to infer past temperatures based on analogs in modern ocean conditions.
When we first looked at the paleoclimatic data, I was struck by the small cooling of the ocean. On average, the ocean was only about two degrees (Celsius) cooler than it is today, yet the planet was completely different—huge ice sheets over North America and northern Europe, more sea ice and snow, different vegetation, lower sea levels and more dust in the air. It shows that even very small changes in the ocean’s surface temperature can have an enormous impact elsewhere, particularly over land areas at mid- to high-latitudes.
—Andreas Schmittner
Schmittner said continued unabated fossil fuel use could lead to similar warming of the sea surface as reconstruction shows happened between the Last Glacial Maximum and today.
Hence, drastic changes over land can be expected. However, our study implies that we still have time to prevent that from happening, if we make a concerted effort to change course soon.
—Andreas Schmittner
Other authors on the study include Peter Clark and Alan Mix of OSU; Nathan Urban, Princeton University; Jeremy Shakun, Harvard University; Natalie Mahowald, Cornell University; Patrick Bartlein, University of Oregon; and Antoni Rosell-Mele, University of Barcelona.
Resources
Andreas Schmittner, Nathan M. Urban, Jeremy D. Shakun, Natalie M. Mahowald, Peter U. Clark, Patrick J. Bartlein, Alan C. Mix, and Antoni Rosell-Melé (2011) Climate Sensitivity Estimated from Temperature Reconstructions of the Last Glacial Maximum. Science doi: 10.1126/science.1203513
This write up should get several responses, especially with the recent climatologist email leaks.
Posted by: Jimr | 25 November 2011 at 09:10 AM
I am bit puzzled that they base their work on the last ice age since temperature change in that case are not determined by increase of greenhouse gas but by change or sun radiance through earth orbit change. There is other work that focus on the oleocene transition when massive amount of CO2 where released and CO2 soared to 1500ppm, a massive climate changed followed that totally changed the face of planet earth in a very short period of time. if we burn all the fossil fuel that we can extract we will reach 1000ppm of CO2 in less than 2 centuries. And then the climate might warm up by 4 or 5C easily. The consequence are simply unthinkable. I prefer prediction that are a bit alarmist and encourage us to take action than prediction that tend to minimize the risk and tell no need to worry and makes lazy to act
Posted by: Treehugger | 25 November 2011 at 09:24 AM
Jimr is apparently referring to;
http://www.uea.ac.uk/mac/comm/media/press/CRUstatements/statements/CRUnov11
http://www.realclimate.org/index.php/archives/2011/11/two-year-old-turkey/
Rehashed quote mining.
Posted by: ai_vin | 25 November 2011 at 02:29 PM
Hmm, a double whammy on climate change today:
"This is a remarkable e-mail since it indicates that the NRC was in collusion with Phil Jones to suppress issues that I brought up as lead author on the CCSP chapter 6. Chapter 6 was tasked to focus on what further research issues need to be explored to reconcile surface and tropospheric temperature trends." Roger Pielke Sr.
https://pielkeclimatesci.wordpress.com/
Anyone else hear the sound of Martin Luther's hammer?? Heading for some rather thorough housecleaning it seems ;>(
Fortunately the transition to electrification and remarkable new forms of low, low cost heat - will be accelerated by these findings! And many new JOBS in SCIENCE and the ARTS are to be delivered. Just part of the very good news.
Posted by: Reel$$ | 25 November 2011 at 05:36 PM
I think there should be less concern about temperature change, and more about pollution. All pollutants are bad and need to be reduced. CO2 is arguably not a pollutant, but like anything else, excess can be bad. Excess CO2 is acidifying our oceans and destroying life, this can have severe consequences to us living on land in the future.
Regardless of climate forcing, reduction of all pollutants and CO2 emissions is paramount.
Best solution is to promote LFTRs. Liquid Flouride Thorium Reactors are inherently safe, produce no long term radio-active waste, and should produce energy cheaper than coal. See flibe-energy.com
Posted by: Roy_H | 25 November 2011 at 07:46 PM
Pielke has a somewhat nuanced position on climate change, which is sometimes taken for skepticism, a label that he explicitly renounces. He has said:
"the evidence of a human fingerprint on the global and regional climate is incontrovertible as clearly illustrated in the National Research Council report and in our research papers"
However, Pielke has criticized the IPCC for its conclusions regarding CO2 and global warming and accused it of selectively choosing data to support a selective view of the science.
In 2010 Pielke revisited a question provided by Andrew Revkin "Is most of the observed warming over the last 50 years likely to have been due to the increase in greenhouse gas concentrations", Pielke stated that the answer "remains No", and that "there are other equally or even more important significant human climate forcings".
http://en.wikipedia.org/wiki/Roger_A._Pielke
http://www.skepticalscience.com/pielke-sr-and-scientific-equivocation-dont-beat-around-the-bush-roger.html
Posted by: ai_vin | 25 November 2011 at 09:22 PM
What happens from here will have little to do with climate "science" and more to do with the ethical and moral failings that caused its corruption. A senior climate scientist has accused leadership of suppressing data and dissenting opinion. Dr. Pielke Sr., will not be going to jail. Others will.
Posted by: Reel$$ | 25 November 2011 at 11:01 PM
A number of separate independent reviews have supported the honesty and integrity of scientists in the Climatic Research Unit, and vindicated the science completely. Links to these reports are here;
http://www.uea.ac.uk/mac/comm/media/press/CRUstatements/independentreviews
Posted by: ai_vin | 26 November 2011 at 08:14 AM
The real ethical and moral failings belong to those who cherry-pick phrases and quote out of context;
http://www.uea.ac.uk/mac/comm/media/press/CRUstatements/rebuttalsandcorrections/phrasesexplained
Posted by: ai_vin | 26 November 2011 at 08:25 AM
http://m.ibtimes.com/police-investigating-climate-email-hackers-255011.html
In a statement immediately after the emails appeared on the Internet Tuesday, the university said: "This appears to be a carefully-timed attempt to reignite controversy over the science behind climate change when that science has been vindicated by three separate independent inquiries and a number of studies."
Posted by: ai_vin | 26 November 2011 at 08:40 AM
Good points RH....GHG is a serious climate issue but many other pollutants adversely affect the well being of humans and most other living entities. The recent rapid rise in autism, cancer, Alzheimer's and many other environment related deceases is still overlooked. Many types of birds and trees have disappeared in the vicinity of many cement, chemical plants and refineries.
The quality of what we drink, eat and breathe is more important than many of us are willing to admit.
Posted by: HarveyD | 26 November 2011 at 10:30 AM
This article and the new release of Climategate emails are simply two, small contributors to the 69% public opinion that some climate "scientists" corrupt data. Surprising? Are we surprised to learn politicians do "favors?" No investigation has been worthy of its title, since investigating one's colleagues rarely produces impartial result.
http://bit.ly/rsvmCq
But the climate campaign was long ago replaced with the positive and uplifting Energy Independence campaign. Where wealthy and poor nations together adopt a whole new source of low cost energy. Development is progressing rapidly now with recent disclosure that major federal agencies have been sponsoring LENR research including DTRA, DARPA, EPRI, and Japan's MITI.
And though some evidence shows DOE involved in manipulating climate data, they have no role in the international commercialization of LENR taking place today. The benefits of a wholly non-radiative, non-polluting, low, low cost source of heat/electricity will broaden the evolution of the human family.
Posted by: Reel$$ | 26 November 2011 at 12:30 PM
RE: http://bit.ly/rsvmCq
69% Say It’s Likely Scientists Have Falsified Global Warming Research
So what? that only goes to show that the wisdom of the masses is NOT wise.
80% believe in the magical sky daddy theory
http://www.rasmussenreports.com/public_content/lifestyle/general_lifestyle/april_2010/80_say_religious_faith_is_important_to_their_daily_lives
76% believe in a 2,000 year old jewish zombie.
http://www.rasmussenreports.com/public_content/lifestyle/holidays/easter_poll_76_believe_jesus_rose_from_the_dead
Depending on which state you live in 76 to 22% believe a group of bronze age goatherders were smarter than us. http://www.rasmussenreports.com/public_content/politics/general_politics/august_2006/75_in_arkansas_alabama_believe_bible_literally_true
and 45-50% believe god created the world less than 10,000 (which is an improvement on the 6,000 year date they believed in only 20 years ago) and that the only reason the dinosaurs aren't with us now is that they missed the boat.
And they elect people who believe as they do.
http://www.juancole.com/2010/11/energy-committee-chairman-candidate-says-god-promised-no-more-catastrophic-climate-change-after-noah.html
Posted by: ai_vin | 26 November 2011 at 02:39 PM
ai_vin, while your attempt to discredit the pollsters is typically plagued by error, it does not change public opinion. And as pointed out before, Pew Research says 51% of members APS believe in God or a "higher power." Whackos?
Details: Your link to the Easter resurrection poll errs greatly - Jesus arose three days after the hammer and nail incident - not 2000 years! And zombies are people infected by some disease: chemical, biological, metaphysical, technological... This link will help:
http://www.thezombienation.com/zombies-defined/
Though you elect to cast the skeptics as religious nutcases (APS!), isn't Lovelaces' Gaia and the cult of greens about the same?
Posted by: Reel$$ | 26 November 2011 at 08:00 PM
I wasn't trying to discredit the pollsters, rather it was the public they were polling.
It is one thing to believe in something you have no evidence for or against, it is quite another to deny the evidence when you have it.
Posted by: ai_vin | 26 November 2011 at 09:12 PM
BTW, I count myself as a skeptic; http://en.wikipedia.org/wiki/Skepticism
in contrast to your denialism; http://en.wikipedia.org/wiki/Denialism
Stop mixing up the two.
Posted by: ai_vin | 26 November 2011 at 09:36 PM
Evidence such as the new trove of Climategate emails??
"This is a remarkable e-mail since it indicates that the NRC was in collusion with Phil Jones to suppress issues that I brought up as lead author on the CCSP chapter 6. Chapter 6 was tasked to focus on what further research issues need to be explored to reconcile surface and tropospheric temperature trends." Dr. Roger Pielke Sr.
https://pielkeclimatesci.wordpress.com/
"Our study shows that very high climate sensitivities are virtually impossible, suggesting that we still have enough time..." said Dr. Andreas Schmittner... lead author.
Posted by: Reel$$ | 27 November 2011 at 02:03 PM
OH, come on ai_vin! Even the notorious Mikey Mann knows the difference between "alarmist" and "skeptic:"
"The panel is solid. Gerry North should do a good job in chairing this, and the other members are all solid. Chris[t]y is the token skeptic, but there are many others to keep him in check." M Mann
And why does a University Climate Research unit want a "strategic partnership" with Goldman (AIG fiasco) Sachs??
date: Mon, 18 May 1998 10:00:38 +010 ???
from: Trevor Davies
subject: goldman-sachs
to: ???@uea,???@uea,???@uea
Jean,
We (Mike H) have done a modest amount of work on degree-days for G-S. They now want to extend this. They are involved in dealing in the developing energy futures market.
G-S is the sort of company that we might be looking for a 'strategic alliance' with. I suggest the four of us meet with ?? (forgotten his name)for an hour on the afternoon of Friday 12 June (best guess for Phil & Jean
- he needs a date from us). Thanks.
Trevor
Professor Trevor D. Davies
Climatic Research Unit
University of East Anglia
http://www.forbes.com/sites/jamestaylor/2011/11/23/climategate-2-0-new-e-mails-rock-the-global-warming-debate/
Posted by: Reel$$ | 27 November 2011 at 02:38 PM
@Reel$$,
For someone who is trying to promote LENR, it seems odd to me that you seem to know all the details and knowledge about what the climate scientists are doing. Should you be informing us about the progress of LENR research and what AR is up to...how many people has AR sold his 1-MW E-Cat reactor to and who they are?
All the climate scientists are doing you a favor! They help warn the public about about the danger of fossil fuel consumption and help you sell LENR to the public. All those who are concerned about the environment should gather on the side of the climate scientists. Their techniques and approaches may not be perfect, but human are inherently imperfect. We should help each other perfect our techniques and method of data collection, instead of wholesale discreting all together those who are on our side, and selling them off to the other side!
Do you know why it is a good idea to align with G-S? For the same reason that presidential candidates need millions of dollars from donors to get their points across, and to overcome disinformation from those with opposing interests. Do you know what the "Golden Rules" are? It's "Those with the Gold make the Rule."
Gee, Reel$$, who has the deepest pocket that would stand to lose the most in the human's move away from fossil fuel? Please kindly help us on that one!
Posted by: Roger Pham | 27 November 2011 at 09:31 PM
Evidence such as the new trove of Climategate emails??
Ah but there's the rub, these aren't a new trove. Check the dates, they are part of the old emails that were investigated after the first "climategate" and three independent inquiries have already cleared the CRU.
Like I said before: Rehashed quote mining.
After you've taken the time to look at the links I've already given above you can also look at this;
http://www.youtube.com/watch?v=4OB2prBtVFo
and if you want to check out the actual emails to see the quotes in context? They are here;
http://foia2011.org/index.php?id=2
If the denialist's case was so solid why do they need to lie about the "evidence?"
Posted by: ai_vin | 27 November 2011 at 09:32 PM
The authors emphasize that global warming is real and that increases in atmospheric CO2 will have multiple serious impacts.
.
.
.
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"Hence, drastic changes over land can be expected. However, our study implies that we still have time to prevent that from happening, if we make a concerted effort to change course soon."
—Andreas Schmittner
Posted by: ai_vin | 28 November 2011 at 07:39 AM
Gentlemen, I do not disagree with the goal: replace fossil with alternative energy. The methods by which that comes about are to date, deficient. Specifically, the "climate campaign" now in final death throes. It is now and has always been an unbelievable strategy. Reliant on hyperbole, hysteria, and phony "science."
@Roger, of course I support LENR as perhaps THE most viable of all alternatives. But human beings do not need climate change to take the needed steps to Energy Independence. We need new sources of energy to accommodate growth at home and in developing nations!
Defending a supposed university "science institute" (Climate Research Unit) getting in bed with G-S, a Wall Street broker of carbon credits, points to extreme ignorance or complicity. The 99% "Occupy Movement" should rightfully camp on the door of CRU. Honesty condemns CRU's behavior.
As for the context of these emails - they are available intact as written for all the world to read and no less damning for it. Political activism in the guise of science regardless of intent - is not science. Never will be. The facts are the climate campaign failed because it relied on inaccurate computer modelling and self-aggrandizing "scientists." And still cannot admit error.
Posted by: Reel$$ | 28 November 2011 at 03:56 PM
Funny how deniers deny that global warming is occurring at all, yet they're all gung-ho over a hint that it may not be quite so bad as it could have been. Then, having no evidence to support their position, they trot out two-year-old gossip and backbiting. Ho hum.
Posted by: richard schumacher | 28 November 2011 at 07:06 PM
Yes, the Earth may be warming or not, as part of a global climate cycle. The campaign was initiated with good intent. Unfortunately once people realized how schemes like cap n' trade could milk TRILLION$$ from business - it went rogue.
We are now fully invested in developing disruptive energy resources. Disruptive short term - constructive long term. We need HELP. We greatly appreciate the HELP we are getting, and we need more. With this HELP the human race will finally be free of the bondage of fossil fuel and combustive energy.
Energy Independence means millions will have light, heat, and fresh water for the first time in (recent) history. This is a good thing. Yes, it realigns the power structure. Yes, it will be disruptive short term. But the opportunity for physical and spiritual growth this offers the human race is divinely inspired, and with HELP will flourish.
Posted by: Reel$$ | 29 November 2011 at 11:42 AM
The most important thing you can do for the long term wellbeing of people is educate them. Information is the one resource that frees the mind so people can find the best solution to their own circumstances.
Misinformation, like the kind you spread about AGW, will lead people to a less than optimal solution just as easily as misinformation about energy independence led them to "drill baby drill," corn ethanol and clean?!?!? coal.
Posted by: ai_vin | 29 November 2011 at 04:25 PM