Paleoclimate data suggests CO2 “may have at least twice the effect on global temperatures than currently projected by computer models”
That’s the subheading of a piece over on Climate Progress covering a new review and analysis of CO2 and temperature data from our Earth’s history. The results are astounding because they show the possibility of much greater warming than climate computer models show due to positive feedback cycles (nothing climate scientists aren’t aware of, to be honest, since they know they do not include these tremendous feedbacks in their models, but something most lay readers are likely not aware of and something of tremendous importance). Here’s a full re-post of Dr Joe Romm’s piece, Science stunner: On our current emissions path, CO2 levels in 2100 will hit levels last seen when the Earth was 29°F (16°C) hotter, since it’s such an important one:
The disinformers claim that projections of dangerous future warming from greenhouse gas emissions are based on computer models. In fact, ClimateProgress readers know that the paleoclimate data is considerably more worrisome than the models (see Hansen: ‘Long-term’ climate sensitivity of 6°C for doubled CO2). That’s mainly because the vast majority of the models largely ignore key amplifying carbon-cycle feedbacks, such as the methane emissions from melting tundra (see Are Scientists Underestimating Climate Change).
Science has just published an important review and analysis of “real world” paleoclimate data in “Lessons from Earth’s Past” (subs. req’d) by National Center for Atmospheric Research (NCAR) scientist Jeffrey Kiehl. The NCAR release is here: “Earth’s hot past could be prologue to future climate.” The study begins by noting:
Climate models are invaluable tools for understanding Earth’s climate system. But examination of the real world also provides insights into the role of greenhouse gases (carbon dioxide) in determining Earth’s climate. Not only can much be learned by looking at the observational evidence from Earth’s past, but such know ledge can provide context for future climate change.
The atmospheric CO2 concentration currently is 390 parts per million by volume (ppmv), and continuing on a business-as-usual path of energy use based on fossil fuels will raise it to ∼900 to 1100 ppmv by the end of this century (see the first figure) (1). When was the last time the atmosphere contained ∼1000 ppmv of CO2? Recent reconstructions (2–4) of atmospheric CO2 concentrations through history indicate that it has been ∼30 to 100 million years since this concentration existed in the atmosphere (the range in time is due to uncertainty in proxy values of CO2). The data also reveal that the reduction of CO2 from this high level to the lower levels of the recent past took tens of millions of years. Through the burning of fossil fuels, the atmosphere will return to this concentration in a matter of a century. Thus, the rate of increase in atmospheric CO2 is unprecedented in Earth’s history.
I will repost the references at the end, since this is a review article (see also U.S. media largely ignores latest warning from climate scientists: “Recent observations confirm … the worst-case IPCC scenario trajectories (or even worse) are being realised” — 1000 ppm)
So now the question is — how much warmer was it back then?
What was Earth’s climate like at the time of past elevated CO2? Consider one example when CO2 was ∼1000 ppmv at ∼35 million years ago (Ma) (2). Temperature data (5, 6) for this time period indicate that tropical to subtropical sea surface temperatures were in the range of 35° to 40°C (versus present-day temperatures of ∼30°C) and that sea surface temperatures at polar latitudes in the South Pacific were 20° to 25°C (versus modern temperatures of ∼5°C). The paleogeography of this time was not radically different from present-day geography, so it is difficult to argue that this difference could explain these large differences in temperature. Also, solar physics findings show that the Sun was less luminous by ∼0.4% at that time (7). Thus, an increase of CO2from ∼300 ppmv to 1000 ppmv warmed the tropics by 5° to 10°C and the polar regions by even more (i.e., 15° to 20°C).
What can we learn from Earth’s past concerning the climate’s sensitivity to greenhouse gas increases? Accounting for the increase in CO2 and the reduction in solar irradiance, the net radiative forcing—the change in the difference between the incoming and outgoing radiation energy–of the climate system at 30 to 40 Ma was 6.5 to 10 W m−2 with an average of ∼8 W m−2. A similar magnitude of forcing existed for other past warm climate periods, such as the warm mid-Cretaceous of 100 Ma (8). Using the proxy temperature data and assuming, to first order, that latitudinal temperature can be fit with a cosine function in latitude (9), the global annual mean temperature at this time can be estimated to be ∼31°C, versus 15°C during pre-industrial times (around 1750) (10). Thus, Earth was ∼16°C warmer at 30 to 40 Ma. The ratio of change in surface temperature to radiative forcing is called the climate feedback factor (11). The data for 30 to 40 Ma indicate that Earth’s climate feedback factor was ∼2°C W−1 m−2. Estimates (1, 11) of the climate feedback factor from climate model simulations for a doubling of CO2 from the present-day climate state are ∼0.5 to 1°C W−1 m−2. The conclusion from this analysis—resting on data for CO2 levels, paleotemperatures, and radiative transfer knowledge—is that Earth’s sensitivity to CO2radiative forcing may be much greater than that obtained from climate models (12–14).
Indeed, in the release, Kiehl notes his study “found that carbon dioxide may have at least twice the effect on global temperatures than currently projected by computer models of global climate.”
Why is the ‘real world’ warming so much greater than the models? The vast majority of the models focus on the equilibrium climate sensitivity — typically estimated at about 3°C for double CO2 (equivalent to about ¾°C per W/m2) — only includes fast feedbacks, such as water vapor and sea ice. As Hansen has explained in deriving his 6°C ‘long-term’ sensitivity:
Elsewhere (Hansen et al. 2007a) we have described evidence that slower feedbacks, such as poleward expansion of forests, darkening and shrinking of ice sheets, and release of methane from melting tundra, are likely to be significant on decade-century time scales. This realization increases the urgency of estimating the level of climate change that would have dangerous consequences for humanity and other creatures on the planet, and the urgency of defining a realistic path that could avoid these dangerous consequence.
For background on the tundra (and methane), see Science: Vast East Siberian Arctic Shelf methane stores destabilizing and venting: NSF issues world a wake-up call: “Release of even a fraction of the methane stored in the shelf could trigger abrupt climate warming.”
Methane release from the not-so-perma-frost is the most dangerous amplifying feedback in the entire carbon cycle. The permafrost permamelt contains a staggering “1.5 trillion tons of frozen carbon, about twice as much carbon as contained in the atmosphere,” much of which would be released as methane. Methane is is 25 times as potent a heat-trapping gas as CO2 over a 100 year time horizon, but 72 times as potent over 20 years! The carbon is locked in a freezer in the part of the planet warming up the fastest (see “Tundra 4: Permafrost loss linked to Arctic sea ice loss“). Half the land-based permafrost would vanish by mid-century on our current emissions path (see “Tundra, Part 2: The point of no return” and below). No climate model currently incorporates the amplifying feedback from methane released by a defrosting tundra.
Kiehl’s work is in line with other major studies, like this one:
Scientists analyzed data from a major expedition to retrieve deep marine sediments beneath the Arctic to understand the Paleocene Eocene thermal maximum, a brief period some 55 million years ago of “widespread, extreme climatic warming that was associated with massive atmospheric greenhouse gas input.” This 2006 study, published in Nature (subs. req’d), found Artic temperatures almost beyond imagination–above 23°C (74°F)–temperatures more than 18°F warmer than current climate models had predicted when applied to this period. The three dozen authors conclude that existing climate models are missing crucial feedbacks that can significantly amplify polar warming.
How long might it take for the extra warming to kick in? That isn’t known for certain, but two major studies looking at paleoclimate data that Kiehl didn’t cite suggest it’s sooner rather than later:
A study published in Geophysical Research Letters (subs. req’d) looked at temperature and atmospheric changes during the Middle Ages. This 2006 study found that the effect of amplifying feedbacks in the climate system–where global warming boosts atmospheric CO2 levels–”will promote warming by an extra 15 percent to 78 percent on a century-scale” compared to typical estimates by the U.N.’s Intergovernmental Panel on Climate Change. The study notes these results may even be “conservative” because they ignore other greenhouse gases such as methane, whose levels will likely be boosted as temperatures warm.
A second study, published in Geophysical Research Letters, “Missing feedbacks, asymmetric uncertainties, and the underestimation of future warming” (subs. req’d), looked at temperature and atmospheric changes during the past 400,000 years. This study found evidence for significant increases in both CO2 and methane (CH4) levels as temperatures rise. The conclusion: If our current climate models correctly accounted for such “missing feedbacks,” then “we would be predicting a significantly greater increase in global warming than is currently forecast over the next century and beyond”–as much as 1.5°C warmer this century alone.
In the longer term, past 2100, if we were to get anywhere near the kind of warming that Kiehl’s analysis of the paleoclimate data suggests we are headed to, that could render large tracts of the planet uninhabitable. That was the conclusion of a recent PNAS paper coauthored by Matthew Huber, professor of earth and atmospheric sciences at Purdue (release here). I haven’t blogged on it, but I guess I will have to now. The bottom line:
“We found that a warming of 12 degrees Fahrenheit would cause some areas of the world to surpass the wet-bulb temperature limit, and a 21-degree warming would put half of the world’s population in an uninhabitable environment,” Huber said. “When it comes to evaluating the risk of carbon emissions, such worst-case scenarios need to be taken into account. It’s the difference between a game of roulette and playing Russian roulette with a pistol. Sometimes the stakes are too high, even if there is only a small chance of losing.”
So don’t even think about what 29°F warming could mean.
Kiehl concludes:
The above arguments weave together a number of threads in the discussion of climate that have appeared over the past few years. They rest on observations and geochemical modeling studies. Of course, uncertainties still exist in deduced CO2and surface temperatures, but some basic conclusions can be drawn. Earth’s CO2concentration is rapidly rising to a level not seen in ∼30 to 100 million years, and Earth’s climate was extremely warm at these levels of CO2. If the world reaches such concentrations of atmospheric CO2, positive feedback processes can amplify global warming beyond current modeling estimates. The human species and global ecosystems will be placed in a climate state never before experienced in their evolutionary history and at an unprecedented rate. Note that these conclusions arise from observations from Earth’s past and not specifically from climate models. Will we, as a species, listen to these messages from the past in order to avoid repeating history?
Will we?
Photo Credit: Roberto Rizzato ►pix jockey◄ Facebook resident
JDoddsGW:
>> First if CO2 causes excess warming the temperature goes up & the Earth radiates the heat away returning to its equilibrium.
So you are saying that if you close the oven door (ie, add insulation), the rise in temperature will be met by more heat loss to the cooler kitchen environment until the temperature inside the oven with the closed door returns back to where it started with the door open?
No, a *new* equilibrium at a higher temperature is created when more insulation is added. This is consistent with the mathematics of the relevant physics of heat loss.
The sun is the power being supplied to the earth/oven. The CO2 is the improved insulation (closing the oven door).
And, no, CO2 gas radiative greenhouse effect across miles of atmosphere doesn’t work exactly like an oven door, but the insulative effect is as real.
>> Second in all these so called feedbacks, just where do they get the extra energy to warm it up? Do they create it out of nothingness.
The sun provides the energy. With greater insulation, the energy dissipates more slowly into space so the average temperature in the heated region is higher since the average quantity of energy at any given point in time is at higher concentration. [This is a rough qualitative description.]
>> Third, there is the simple fact that there is excess GHGs both water vapor and CO2 in the air.
I don’t know what you mean, but at higher temperature more water vapor can dissolve into the air and will leave the oceans. Ditto for CO2 that might be in the oceans; however, so much CO2 is in the air for the current temperature that there is a net movement of CO2 today from the air into the oceans. This trend is slowing, which means a greater fraction of the CO2 being put into the air is staying there.
>> WHen the CO2 is added by man, all the CO2 absorbable photons have already been put to work, there are no more to be absorbed
The sun has a virtually infinite supply of photons it sends our way. The more CO2 (and even if we add other nonGHG gases by increasing the pressure.. as long as there is at least some GHG gases to work as the conduit), the more photons will remain longer in the atmosphere.
>> MOre GHGs does NOT means more warming if all the photons are already in use and there are excess GHGs.
If you have math to support your claims, please debate this with atmospheric and radiation physicists.
There is another, even more inconvenient truth. Climate scientists for the most part base their predictions on the effects of CO2, and to a lesser extent methane, whether using models or comparing levels of CO2 in the atmosphere in the past to temperature.
They almost universally do not factor in the other emissions from burning fuel, even though they are more potent, because they exist in much smaller quantities and they also do not persist for centuries as will CO2.
However, this leads them to discount two crucial problems.
1. The aerosols are blocking out the sun, reducing the amount of sunlight that reaches earth’s surface by significant amounts. If the aerosols weren’t there, climate change would already be much more accelerated than it already is. If we stop polluting – either because it’s a bad thing to do, or because industrial civilization collapses due to, say, peak oil, it will become very much hotter, very quickly.
2. The background level of tropospheric ozone is inexorably rising as volatile organic compounds are released from burning coal and oil. There is no paleoclimatic comparison for what this might mean, because there has never before been a significant amount of ozone at ground level. Unfortunately, it turns out that ozone is toxic, causing cancer, emphysema, asthma, allergies, diabetes and autism in humans. Worse still, it is even more poisonous to plants. Ozone interferes with the ability of vegetation to photosynthesize. NASA estimates annual crop yield reductions in the US in the billions of dollars. Every major crop around the globe is being stunted, from rice to wheat to cotton to soybeans.
Think then of what the cumulative exposure does to longer-lived species like trees. They are dying at a rapidly accelerating rate. In addition, they are producing fewer nuts and seeds, which are of declining nutritive value. You’d expect with the root systems of vegetation shrinking there would be mudslides all over the world, and wild animals like birds wouldn’t have enough to eat and would be falling, dead, out of the skies…
oh, wait.
excellent additional points, WitsEnd
some climate scientists and papers discuss methane and other factors but, as you said, mostly left out, underestimating likely effects
global warming is the greatest hoax!!!!
mbmbmb, thanks for your insightful comment. you must have missed the memo, though. it is not a hoax & your children and grandchildren (if you have them) will likely look down on you for thinking so
Why did we scare our kids with the CO2 death threat just to get them to turn the lights out and the thermostat down more often?
Pollution was real but this fear mongering wasn’t sustainable, especially for progressivism that preaches love and harmony.
Climate Change was a mistake, our Iraq War and is now dividing progressivism and environmentalism. The deniers won.
We need System Change, not Climate Change and let’s act like real liberals again. Real liberals don’t lick the boots of the likes of fat politicians as he promises to take our taxes and make the weather colder.
Let’s admit the deniers have won and admit our exaggerations and put this insanity behind us and get back to responsible stewardship of the planet.
John Larl, i don’t know why you think deniers have won. the only way you could view it that way is by seeing that the U.S. Republican party is the only major party in the world to deny climate science (and even science in general in some instances) bcs it is bought out by the dirty energy industry, and the same dirty energy industry has convinced much of the American public that climate change is a hoax. it is far from it. my bet is that those who understand this matter are not traumatizing their kids either, but more likely educating them to understand science and grow up to be a good, mature adult
What uneducated “scientists”
First if CO2 causes excess warming the temperature goes up & the Earth radiates the heat away returning to its equilibrium.
Second in all these so called feedbacks, just where do they get the extra energy to warm it up? Do they create it out of nothingness.
Third, there is the simple fact that there is excess GHGs both water vapor and CO2 in the air. If there is excess then it is the number of energy photons that dictates how much Greenhouse warming we can get, otherwise the excess water vapor (in the ocean) would just continue warming as it all vaporized. WHICH IT DOES NOT. This means that Arrhenius was wrong in 1896, when he said more GHGs means more warming. It is the available number of photons that dictates the GHE Warming. MOre sunshine or more gravity or more Potetnial energy from passing planets means more warming- ALL of which Man can NOT control.
What energy, not GHGs, as in morning warming by the sun, controlling the GHE warming means is that the HAnsen water vapor feedback effect does not exist. When man adds more CO2 it just adds to the excess in the air. What water vapor GHE heating occurs actually happens by direct sunlight to IR to water vapor absorbtion. WHen the CO2 is added by man, all the CO2 absorbable photons have already been put to work, there are no more to be absorbed, so the added CO2 does NOT cause added warming, which does NOT result in more added WV or added WV warming , so there is no WV “feedback” effect. What WV warming there is comes form the WV absorbing the photons up until they put all the photons to use.
WHat this means is that the computer models are not accurate. MOre GHGs does NOT means more warming if all the photons are already in use and there are excess GHGs.
IN other words, the climate scientists can not do climate science very well/ starting with Arrhenius and going through Hansen, to Kiehl et al.
JDoddsGW: this is so off and full of holes it is funny. i’m sorry, but your very simplistic and flawed explanation of how the climate is effected by different things does not disprove the sound scientific findings of these climate scientists, whose work has been vindicated by some of the top scientific organizations in the world
If it is so full of holes, flawed and simplistic, feel free to use your own detailed scientific knowledge to refute it.
Or is this just a case of only listening to selected scientists who say what you want to hear, and ignoring everything said by scientists whose findings run counter to your prejudices?
What holes? Prove it! Cite the flaws in the logic.
Look at the Arrhenius paper. Arrhenius doesn’t even look at the reality of how much CO2 in on the Earth, he just assumes there is enough photons for all the CO2. Why does teh GHE stop at about 33C? His science equation doesn’t even allow for a limitation on either the number of photons OR the number of CO2s. Which obviously will stop the GHE.
Can you deny that the greenhouse effect requires an energy photon plus a GHG?
Then which one is in the majority? Is there more energy than GHGs In which case why doesn’t the warming effect continue until all the water is vaporized? SO it must be that the number of energy photons is in the minority. IN which case the warming continues until all the energy is in use, at which time you can NOT get any more warming.
It is simple common sense scientific logic that seems to be lacking in the science of climate scientists. WHo just like Arrhenius want to prove a preconceived notion even if it is absurd.
As for the scientific organizations do you think they are going to say global warming is natural, we can’t do anything about it, so we do not want your research money?
John & Autonomous Mind: it is a rambling, scattered explanation not worth spending time on. I mean, seriously, if you believe what is written there, I don’t think there’s much counter-argument that’s going to add sense to your thinking. I’ve had a million and one back-and-forths around such topics — can spot a hopeless cause when it walks into the room.
We just love you arm chair amateur climatologists. As a climate change believer, you are to obey, not think. Get back in line and do as you are told and spare us your personal and non scientific definitions of THE END IS NEAR.
Cathy Keen, I’ve learned about climate science in-depth for a long time now. i did not pursue it in school years ago as I chose to pursue solutions to it instead. I’m sure I’ve spent a lot more time reading the scientific literature on climate change than you can imagine, though. of course, that is all rigged, isn’t it? (your news sources would probably have you think so)
The evidence is accumulating. We have ruined our planet, and are sliding helplessly into an extinction event that includes humanity in its scope.
What can now prevent methane catastrophe?
Bill, thanks a lot for your comment. & yes, if we don’t switch to a clean energy economy and this climate feedback occurs, that could be a leading questions scientists and big govt will have to address. ironic that deniers are afraid of addressing climate change now bcs of big govt, given that big govt will have to step in to such a greater degree in the future if we delay now
The Deniers Have Won.
Now we charge the news editors with treason for leading us to a Bush-like false war against a false enemy of climate change.
Climate Change did to journalism and science what abusive priests did to religion.
Drop the CO2 and restart environmentalism anew with courage, instead of fear.
odd remark considering that the public is far more doubtful and confused about climate change than the scientists and given the fact that journalists and the mass media give approx. equal weight to the arguments of 3% of publishing climate scientists as they do to 97% of publishing climate scientists (to keep the debate “even”)
It’s easy to be a glowbull Doomer or climate change blamer still because personal definitions of climate crisis give you faded Doomers a free pass. Times up and as you feel squeezed when threatening other people’s kids with your CO2 death threats, just wait till the Senate hearings.
We never got Bush for his WMD’s but we will not miss this opportunity for SYSTEM CHANGE, NOT CLIMATE CHANGE.
Let’s be REAL liberals again and REAL environmentalists again.
Harry Leen, human-accelerated climate change is not a political claim — it is a scientific fact. clearly, an important point.