Cloud feedback to global warming

[vox_mundi]

Global Satellite Data Shows Clouds Will Amplify Global Heating
https://phys.org/news/2021-07-global-satellite-clouds-amplify.html

Research, by scientists at Imperial College London and the University of East Anglia, is the strongest evidence yet that clouds will amplify global heating over the long term, further exacerbating climate change.

The results, published today in Proceedings of the National Academy of Sciences, also suggest that at double atmospheric carbon dioxide (CO2) concentrations above pre-industrial levels, the climate is unlikely to warm below 2°C, and is more likely on average to warm more than 3°C.

Inspired by ideas from the artificial intelligence community, the researchers developed a new method to quantify relationships between state-of-the-art global satellite observations of clouds, and the associated temperature, humidity and wind conditions. From these observed relationships, they were then able to better constrain how clouds will change as the Earth warms.

They found it was very likely (more than 97.5% probability) that clouds will amplify global heating, by both reflecting less solar radiation and enhancing the greenhouse effect. These results also suggest that a doubling of CO2 concentrations will lead to around 3.2°C of warming. This is the highest confidence of any study so far, and is based on data from global observations, rather than local regions or specific cloud types.

Paulo Ceppi el al., "Observational evidence that cloud feedback amplifies global warming," PNAS (2021).
https://www.pnas.org/content/118/30/e2026290118

[The Walrus]

I find their reasoning rather dubious.  While the do show strong evidence that clouds will enhance the greenhouse effect, evidence supporting their conclusion that clouds will reduce the reflection of solar radiation is severely lacking.

[kassy]

Some details via Eurekalert:

Global satellite data shows clouds will amplify global heating

...

The largest uncertainty in climate sensitivity predictions is the influence of clouds, and how they may change in the future. This is because clouds, depending on properties such as their density and height in the atmosphere, can either enhance or dampen warming.

Co-author Dr Paulo Ceppi, from the Grantham Institute - Climate Change and the Environment at Imperial, said: "The value of the climate sensitivity is highly uncertain, and this translates into uncertainty in future global warming projections and in the remaining 'carbon budget' - how much we can emit before we reach common targets of 1.5°C or 2°C of global warming.

"There is therefore a critical need to more accurately quantify how clouds will affect future global warming. Our results will mean we are more confident in climate projections and we can get a clearer picture of the severity of future climate change. This should help us know our limits - and take action to stay within them."

Low clouds tend to have a cooling effect, as they block the sun from reaching the ground. High clouds, however, have a warming effect, as while they let solar energy reach the ground, the energy emitted back from the Earth is different. This energy can be trapped by the clouds, enhancing the greenhouse effect. Therefore, the type and amount of cloud a warming world will produce impacts further warming potential.

...

Co-author Dr Peer Nowack, from the School of Environmental Sciences and Climatic Research Unit at the University of East Anglia and Imperial's Grantham Institute and Data Science Institute, said: "Over the last few years, there's been a growing amount of evidence that clouds probably have an amplifying effect on global warming. However, our new approach allowed us for the first time to derive a global value for this feedback effect using only the highest quality satellite data as our preferred line of evidence.

https://www.eurekalert.org/pub_releases/2021-07/icl-gsd071521.php

So they have sat data which shows which type of clouds are where not in space but also in height.

In general as the atmosphere warms it holds more vapor which means that low clouds will form later if you keep all else the same.

[kassy]

This thread is for science about the cloud feedback to global warming in general.

Discussion of aerosols and their direct influence has it´s own thread:
https://forum.arctic-sea-ice.net/index.php/topic,1384.0.html

[oren]

You need to edit the subject of the top post.

[kassy]

You need to edit the subject of the top post.

Oops. Modified them all now.

[kassy]

Since the cloud effect has been uncertain, its accurate measurement also helps affirm other recent projections that a doubling of carbon dioxide in the atmosphere will warm the planet’s surface by about 5.8 degrees Fahrenheit, said said co-author Paulo Ceppi, a climate scientist with the Grantham Research Institute on Climate Change at Imperial College London.

“Most previous cloud studies focused only on certain regions or regimes, so say they look at places where there are low clouds and they look at low clouds only,” he said. “We did this analysis everywhere, at every point regardless of what type of cloud was there, and that allowed us to get a global picture.”

The new research is an important update to the scientific understanding of clouds in the climate system, said Piers Forster, director of the Priestley Centre at Leeds University.

“It is a really good step forward,” said Forster, who was not involved in the new study, but has worked on other recent research assessing the climate system’s response to building greenhouse gas levels.

“It really tells us how clouds respond to changes in local surface temperature, especially the reflectance of low clouds,” he said. “This is then used to make an accurate estimate of the total cloud feedback: the amplifying effect that clouds have on global warming.”

To get a sense of how important clouds are in the global warming equation, Ceppi said their effects can be compared to the warming effect of carbon dioxide.

“We calculate that, on average globally, clouds reflect something like 50 watts per square meter of solar radiation,” he said. “You can compare that to the forcing from a doubling of CO2, which would be about 4 watts per square meter, much smaller than the average effect of clouds on sunlight. So even a very small change in how much sunlight is reflected by clouds would be comparable to the effect of a CO2 doubling.”

In general, the new research confirms what some of those other studies have suggested, he said.

“People have argued that clouds will amplify global warming because of solar impacts, so less reflected sunlight from low clouds, but also because of the greenhouse effect of clouds, where high clouds rise, which makes them have a larger warming effect,” he said. “Our study finds evidence of both. I’m not aware of any other studies that have been able to show that, especially the greenhouse part.”

One recent study, led by University of Oslo researchers, shows global warming will reduce the amount of ice particles in widespread low clouds around Antarctica that currently reflect a huge amount of solar radiation back into space. That would make the clouds less reflective and amplify global warming, said cloud researcher Trude Storelvmo.

https://insideclimatenews.org/news/19072021/climate-driven-changes-in-clouds-are-likely-to-amplify-global-warming/

Even more detailed info on how clouds work/what they detected in general.

The last paragraph is a bonus mention of another troubling feed back.

[jai mitchell]

This thread is for science about the cloud feedback to global warming in general.

Discussion of aerosols and their direct influence has it´s own thread:
https://forum.arctic-sea-ice.net/index.php/topic,1384.0.html

The problem here is that the two are causally linked but this causation has not been proven conclusively through scientific analysis, either through lack of information and understanding or simply due to the lack of effort and focus on it.

For instance, scientific study in 2012 at UK Leeds showed that the Atlantic Multi-decadal Oscillation was driven by regional aerosol loading, this was called into question and now this result is still uncertain.

Similarly, Michael Mann led a paper recently that declared that the Pacific Decadal Oscillation was driving primarily by Volcanic activity.

However, if you look at the Pacific Decadal Oscillation series, you see quite clearly that high global aerosol loading is linked with a long and persistent negative phase of the PDO and that subsequent to short term Aerosol reduction activities the PDO swings positive. 

This happened during the swing in 1978, our most recent period of warming acceleration prior to 2014, when China successfully reduced their aerosol emissions enough to swing the PDO positive (who would have thought that SE Asian aerosols would have a stronger effect on the Pacific???)

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and now the point
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The pattern effect cloud studies have shown that the pattern effect from warming is only really extracted from the data after 2014 when the PDO went positive.

If I am correct, then we will see a strong positive PDO prevalence and that this will increase with forcing into a permanent positive PDO.  This will show that the pattern effect is a significant percentage of the total GHG forcing as a short-term feedback, adding to the lapse rate and water vapor feedbacks. 

And that ECS is greater than 4.5K

[kassy]

Clouds That Can No Longer Cool

The other recent cloud study, led by University of Oslo scientists, showed that global warming will eventually cut the volume of ice particles in massive cloud banks over the Southern Ocean, around Antarctica.

“The ice in those clouds makes them brighter and more reflective, but if we allow enough warming, there won’t be any more ice,” said University of Oslo climate researcher Trude Storelvmo, co-author of the study, published Oct. 26 in the journal Nature Geoscience.

The findings suggest that, if the average global temperature increases by 5 to 7 degrees Fahrenheit, the clouds over the Southern Ocean would lose their cooling effect and further raise the global temperature by an additional 2 to 3 degrees.

Figuring out exactly how sensitive the climate is to rising greenhouse gas concentrations depends in large part on knowing what happens to clouds, and the computer models have to use correct information to end up with accurate projections.

“We have to start at the right point to be able to simulate how it will change over time, and we haven’t had good measurements on this particular cloud property,” Storelvmo said. “But now we have these wonderful new measurements that have really changed things,” she continued, describing the lidar and radar readings that can show the ratio of water to ice inside the clouds much more accurately than just 10 years ago.

“In this model, we saw that, when we had warming of 3 to 4 degrees Celsius (5.4 to 7.2 degrees Fahrenheit), we had no more ice,” she said. At that point, the clouds lose their cooling effect.

https://insideclimatenews.org/news/10112020/clouds-cooling-climate-effects/