PRINCETON UNIVERSITY
A recent analysis of the latest generation of climate models — known as a CMIP6 — provides a cautionary tale on interpreting climate simulations as scientists develop more sensitive and sophisticated projections of how the Earth will respond to increasing levels of carbon dioxide in the atmosphere.
Researchers at Princeton University and the University of Miami reported that newer models with a high “climate sensitivity” — meaning they predict much greater global warming from the same levels of atmospheric carbon dioxide as other models — do not provide a plausible scenario of Earth’s future climate.
Those models overstate the global cooling effect that arises from interactions between clouds and aerosols and project that clouds will moderate greenhouse gas-induced warming — particularly in the northern hemisphere — much more than climate records show actually happens, the researchers reported in the journal Geophysical Research Letters.
Instead, the researchers found that models with lower climate sensitivity are more consistent with observed differences in temperature between the northern and southern hemispheres, and, thus, are more accurate depictions of projected climate change than the newer models. The study was supported by the Carbon Mitigation Initiative (CMI) based in Princeton’s High Meadows Environmental Institute (HMEI).
These findings are potentially significant when it comes to climate-change policy, explained co-author Gabriel Vecchi, a Princeton professor of geosciences and the High Meadows Environmental Institute and principal investigator in CMI. Because models with higher climate sensitivity forecast greater warming from greenhouse gas emissions, they also project more dire — and imminent — consequences such as more extreme sea-level rise and heat waves.
The high climate-sensitivity models forecast an increase in global average temperature from 2 to 6 degrees Celsius under current carbon dioxide levels. The current scientific consensus is that the increase must be kept under 2 degrees to avoid catastrophic effects. The 2016 Paris Agreement sets the threshold to 1.5 degrees Celsius.
“A higher climate sensitivity would obviously necessitate much more aggressive carbon mitigation,” Vecchi said. “Society would need to reduce carbon emissions much more rapidly to meet the goals of the Paris Agreement and keep global warming below 2 degrees Celsius. Reducing the uncertainty in climate sensitivity helps us make a more reliable and accurate strategy to deal with climate change.”
The researchers found that both the high and low climate-sensitivity models match global temperatures observed during the 20th century. The higher-sensitivity models, however, include a stronger cooling effect from aerosol-cloud interaction that offsets the greater warming due to greenhouse gases. Moreover, the models have aerosol emissions occurring primarily in the northern hemisphere, which is not consistent with observations.
“Our results remind us that we should be cautious about a model result, even if the models accurately represent past global warming,” said first author Chenggong Wang, a Ph.D. candidate in Princeton’s Program in Atmospheric and Oceanic Sciences. “We show that the global average hides important details about the patterns of temperature change.”
In addition to the main findings, the study helps shed light on how clouds can moderate warming both in models and the real world at large and small scales.
“Clouds can amplify global warming and may cause warming to accelerate rapidly during the next century,” said co-author Wenchang Yang, an associate research scholar in geosciences at Princeton. “In short, improving our understanding and ability to correctly simulate clouds is really the key to more reliable predictions of the future.”
Scientists at Princeton and other institutions have recently turned their focus to the effect that clouds have on climate change. Related research includes two papers by Amilcare Porporato, Princeton’s Thomas J. Wu ’94 Professor of Civil and Environmental Engineering and the High Meadows Environmental Institute and a member of the CMI leadership team, that reported on the future effect of heat-induced clouds on solar power and how climate models underestimate the cooling effect of the daily cloud cycle.
“Understanding how clouds modulate climate change is at the forefront of climate research,” said co-author Brian Soden, a professor of atmospheric sciences at the University of Miami. “It is encouraging that, as this study shows, there are still many treasures we can exploit from historical climate observations that help refine the interpretations we get from global mean-temperature change.”
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The paper, “Compensation Between Cloud Feedback and Aerosol?Cloud Interaction in CMIP6 Models,” was published in the Feb. 28 edition of Geophysical Research Letters. The research was supported by the National Oceanic and Atmospheric Administration (grants NA20OAR4310393 and NA18OAR4310418) and the Carbon Mitigation Initiative based in Princeton University’s High Meadows Environmental Institute (HMEI).
No it does not! It says it would be really nice to keep it “much lower” than 2 deg C. It does not change the fictitious “threshold” which itself was pulled out of the air ( to put it politely ).
Who wrote the text of this post?
Which part(s)— if any— were part of the Princeton press release?
Which part(s)— if any— were written by Charles Rotter?
Why did earth not get stuck in a hot house scenario when CO2 was 2000 ppm ?
Answer: There are many negative feedback mechanism, most of them probably due to the fact that earth is covered to 73% by water. It is time for the climate gamers to install that into their toy models.
Researchers at Princeton University and the University of Miami reported that newer models with a high “climate sensitivity” — meaning they predict much greater global warming from the same levels of atmospheric carbon dioxide as other models — do not provide a plausible scenario of Earth’s future climate.
The above statement is the only segment I agree with. The remainder is propaganda.
This is an interesting paper that I’m still trying to unpack, but we should be careful in the implications being drawn from it. The results of this study indicate that the highest-sensitivity models are not capturing observed historic spatial patterns in cloud response, but it does not mean that climate sensitivity is low. I think it’s been known for a while that the highest CMIP6 estimates are almost certainly too high, this paper just sheds some light on why.
For anyone wondering where this latest troll spung forth from.
https://www.reddit.com/user/Weekly_Rise/
”Theres no established connection between the strength of the solar cycle and global temperature trends”
And if that isn’t weapons grade trolling i don’t now what is.
[QUOTE]Researchers at Princeton University and the University of Miami reported that newer models with a high “climate sensitivity” — meaning they predict much greater global warming from the same levels of atmospheric carbon dioxide as other models — do not provide a plausible scenario of Earth’s future climate.
Those models overstate the global cooling effect that arises from interactions between clouds and aerosols and project that clouds will moderate greenhouse gas-induced warming — particularly in the northern hemisphere — much more than climate records show actually happens, the researchers reported in the journal Geophysical Research Letters. [END QUOTE]
Why would models that “overstate the global cooling effect” due to clouds result in higher predicted temperatures? Wouldn’t they result in lower predicted temperatures?
Of course, the whole idea of a “climate sensitivity” to CO2, with a supposedly fixed temperature increase for every doubling of CO2 concentration, is not based in physical reality, but on a faulty equation proposed in 1906 by Svante Arrhenius, which the IPCC never bothered to revise or replace by an equation based on the physics of IR absorption by gases.
I wrote about this in detail in a previous post a few days ago, but in summary, the total warming due to CO2 in clear weather would follow a relationship of the form
dT(z) = K* Io [1 – exp(-ACz)]
where
dT (z) = temperature rise as a function of altitude
Io = IR radiation intensity from Earth’s surface, a function of temperature and wavelength
A = IR absorption coefficient, a function of wavelength
C = CO2 concentration
z = altitude above Earth’s surface
The constant K would have to be evaluated by integrating over all IR wavelengths. This equation is based on Beer’s law for IR absorption by gases.
First of all, the total possible warming due to CO2 is limited to K * Io, which is the limit of the function as C goes to infinity. This illustrates the saturation effect–if the CO2 concentration is high enough, all the available energy is absorbed, and further increases have no further warming effect, they only concentrate the warming at a lower altitude.
The net effect of a doubling of CO2 would also vary by wavelength and altitude. Suppose that, at a given wavelength at current CO2 concentrations, ACz = 2.0, which means that the current warming due to CO2 would be 0.8647 K*Io. If C is doubled, ACz becomes 4.0, in which case the total warming due to CO2 would be 0.9817 K*Io, so that doubling the CO2 concentration increases the temperature by 0.1170 K*Io. If the CO2 concentration is doubled again, ACz = 8.0, and the total warming becomes 0.9997 K*Io, so the second doubling produces a net increase of 0.0180 K*Io, or about 6.5 times less warming than the first doubling.
This shows that “climate sensitivity” to a doubling of CO2 concentration is NOT a constant, but it decreases sharply as CO2 concentrations increase. A third doubling would cause an increase of less than 0.0003 K*Io, which would be negligible.
“Why would models that “overstate the global cooling effect” due to clouds result in higher predicted temperatures?”
I noticed that, too, while reading the article.
I think the author meant to say “understate” rather than “overstate”.
Here’s an idea for a model. If you perform a simple mathematical transformation on GHG radiation in the Earth’s energy domain (atmosphere + surface) you get a rather interesting result. The transformation is: change every event (emission + reabsorption) to an average one. When you do this the overall energy flow should be identical. Each photon that leaves the surface will stop N times as it is reabsorbed. Each photon will travel a distance of X meters towards space before being reabsorbed. It will take T seconds for each event to complete.
Notice this transformed system has no downwelling IR. Yet, it is mathematically equivalent to our current atmosphere. So much for the greenhouse effect. Now, what will happen if you add more GHGs to the energy domain? Since GHGs already absorb all the radiation coming up from the surface that it can absorb, the most it can do on the absorption side is slow the process down slightly. N would get larger, X would get shorter and T a little longer. However, you are also adding more emitters which naturally has the opposite effect. The two would likely cancel out. The only way to warm the system is to add more energy to it.
Can anyone tell me why this isn’t a valid transformation? I think this is telling us something important.
You are proving the models failed?
Why would you accept “NASA’s Goddard Institute for Space Studies Surface Temperature Analysis project” data to be true?
We’re having failed models AND fake data here. None of the lines are anywhere correct, neither the red-, the blue- nor the black line.
Oddgeir