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???)

--------------
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/

[kassy]

One of climate change's great mysteries is finally being solved


For over a decade, the largest scientific uncertainty about how the planet will respond to warming temperatures hasn’t come from how much carbon dioxide will be soaked up by the ocean or absorbed by the trees. It’s come, instead, from clouds.

The fluffy, whimsical collections of water droplets floating in the air have, for some time, confounded climate scientists and models alike. Scientist have long known that depending on how clouds respond to warming temperatures, the world could become even warmer or a little bit cooler. They just haven’t known which.

But in the past few years, scientists have begun to nail down exactly how clouds will change shape and location in the rapidly warming world. The result is good news for science – but not good news for humanity.

“We’ve found evidence of the amplifying impact of clouds on global warming,” said Paulo Ceppi, a climate scientist at Imperial College London.

Scientists have long known that clouds have two primary influences on the global climate. First, clouds are reflective – their white surfaces reflect the sun’s rays away from Earth, creating a cooling effect. (If the planet were suddenly devoid of these fluffy parasols, the planet would be roughly five times hotter than even the most disastrous global warming projections.)

But clouds also create a warming effect – certain types of clouds insulate the Earth’s radiation, keeping the planet warm much like carbon dioxide released from the burning of fossil fuels.

Which effect is stronger depends on the type of cloud. Cirrus clouds – high, wispy clouds visible in the distant atmosphere on relatively clear days – absorb and trap more radiation, warming the Earth. Stratus or stratocumulus clouds – plump, fluffy clouds that often hover over the ocean on overcast days – reflect more sunlight, cooling the Earth.

How exactly those two factors will balance out as the world warms has been uncertain. That’s mostly because, even though clouds can look gigantic – when you are flying through them in a plane or looking up at them from the ground – they form at microscopic levels, when water vapour condenses around a particle of dust or a droplet.

As a result, they are essentially impossible to model in the standard big climate models. (Clouds form at the micrometer level, while the models that most climate scientists use separate the world into blocks hundreds of kilometres in width.)

“We have a really tough time simulating with any fidelity how clouds actually behave in the real world,” said Timothy Myers, a postdoctoral researcher at the Lawrence Livermore National Laboratory in California.

But in recent years, scientists have gained increasing clarity on what will happen – and what is already happening – to clouds as the planet warms.

First, the high, wispy cirrus clouds that trap the Earth’s radiation are expected to shift upward in the atmosphere, to lower temperature zones. Thanks to a complicated relationship between clouds and the radiation of the Earth, that will increase the amount of radiation that the cirrus clouds trap in the atmosphere.

“When they rise, their greenhouse effect, or warming effect, on the Earth tends to increase,” Myers said.

That result has been known for about a decade, and indicates that clouds are likely to amplify global warming. But just in the past few years, researchers have also discovered that the number of low-level stratus or stratocumulus clouds are expected to decrease as the planet continues to warm.

One study, in the journal Nature Climate Change, used satellite observations to discover how cloud formation is affected by ocean temperatures, wind speed, humidity and other factors – and then analysed how those factors will change as the world warms.

“We concluded that as the ocean warms, the low-level clouds over the oceans tend to dissipate,” said Myers, one of the authors of the study. That means that there are fewer clouds to reflect sunlight and cool the earth – and the change in low-level clouds will also amplify global warming.

Another paper, in the Proceedings of the National Academy of Sciences, found a similar result, also using observational techniques. Research based on high resolution models – which are better able to model cloud formation than general, larger-scale climate models – have also concluded that clouds are likely to amplify global warming.

...

According to another study released last month in the Proceedings of the National Academy of Sciences, sulfate aerosols have spurred cloud formation, thus masking some of the global warming that has already occurred.

...

Scientists once estimated that if CO2 reached 560 ppm, the temperature would increase between 1.5 and 4C – a range that spans a “still very liveable planet” to “near-apocalypse levels of warming”.

A great deal of that uncertainty has stemmed from the question of clouds. Because clouds are so influential on the Earth’s climate already, even small changes in clouds as the world warms can have large effects on future temperature change.

The new cloud research indicates that the lower estimates for warming are highly unlikely. Instead, the recent papers estimate that CO2 levels of 560 ppm would probably result in at least 3 or 3.5 degrees of warming.

...

https://www.stuff.co.nz/environment/climate-news/300763418/one-of-climate-changes-great-mysteries-is-finally-being-solved

[jai mitchell]

Paper just came out that shows the total climate feedback (including cloud and pattern effect) is enough forcing to be responsible for ALL of the observed warming from 1980-2014

This means that there is still a lot of warming left

https://journals.ametsoc.org/view/journals/clim/36/18/JCLI-D-22-0862.1.xml
Observational Constraints on the Cloud Feedback Pattern Effect
Timothy A. Myers, Mark D. Zelinka , and Stephen A. Klein
Online Publication: 28 Aug 2023

Abstract
Model evidence for the “pattern effect” assumes that global climate models (GCMs) faithfully simulate how clouds respond to varying sea surface temperature (SST) patterns and associated meteorological perturbations. We exploit time-invariant satellite-based estimates of the sensitivity of marine low clouds to meteorological perturbations to estimate how these clouds responded to time-varying SST patterns and meteorology between 1870 and 2014. GCMs and reanalyses provide estimates of the historical meteorological changes. Observations suggest that increasing estimated inversion strength (EIS) between 1980 and 2014 produced a negative low cloud feedback, opposite to the positive feedback expected from increasing CO2. This indicates that the processes responsible for marine cloud changes from 1980 to the near present are distinct from those associated with an increase in CO2. We also observationally constrain the difference between the historical near-global marine low cloud feedback, λhistcloudand that arising from increasing CO2. We find that this cloud feedback pattern effect depends strongly on time period and reanalysis dataset, and that varying changes in EIS and SST with warming explain much of its variability. Between 1980 and 2014, we estimate that 0.78 (90% confidence) assuming meteorological changes from the Multiple Reanalysis Ensemble, implying a total pattern effect (that arising from all climate feedbacks) of 1.86 ± 0.45 W m−2 K−1. This observational evidence corroborates previous quantitative estimates of the pattern effect, which heretofore relied largely upon GCM-based cloud changes. However, disparate historical meteorological changes across individual reanalyses contribute to considerable uncertainty in its magnitude.

[kassy]

Rise In Global Thunderstorm Activity Might Increase The Quantity Of Wispy Cirrus Clouds – Accelerating Global Warming


A new study has found a significant statistical correlation between thunderstorms occurring around the world and the formation of wispy cirrus clouds – which might increase global warming. The researchers: “We know that cirrus clouds can contribute to global warming. However, it is very difficult to track these clouds and obtain accurate data about them. Our findings indicate that a rise in the number of thunderstorms occurring globally might significantly increase the quantity of cirrus clouds, thereby exacerbating the climate crisis.”

...

Prof. Price explains: “Cirrus clouds, those feathery clouds we see in the sky, significantly impact the earth’s climate. An increase of these clouds will act as a blanket that increases warming, while a decrease will allow the heat of the Earth to rise and escape from the atmosphere. This is why climate researchers are highly interested in cirrus clouds, trying to predict potential changes due to the rise in greenhouse gases and global warming. But here we encounter a significant problem: it is very hard to obtain accurate, comprehensive data about cirrus clouds. Being so wispy, they can be invisible to the human eye and even to satellites, plus they form in the upper atmosphere, far from the monitoring stations operating on the ground.”

To address this challenge the researchers explored the possibility of predicting the quantity of cirrus clouds on the basis of readily available data about thunderstorms and lightning activity. They explain that the brilliant flash of lightning is formed when a huge electric field is discharged instantaneously, generating a very high temperature of up to 30,000 degrees Centigrade in the lightning channel. The light waves and radio waves emitted by the lightning discharge can be detected even thousands of kilometers away, enabling long-term monitoring and mapping of thunderstorms.

The present study is based on thunderstorm data collected worldwide over a period of 6 years by the NASA satellite ISS-LIS that detects the light emitted by lightning. The researchers compared these data with data on cirrus clouds (the partial information available combined with supplementary models), looking for a correlation between lightning activity on a specific day, month, or year, and the amount of cirrus clouds formed in the upper atmosphere. Findings indicate a statistically significant correlation, with the quantity of cirrus clouds increasing with the number of thunderstorms. According to the researchers, this means that thunderstorms, which are easy to detect and measure, can in fact be used as a reliable indicator for the amount of cirrus clouds in the atmosphere, today and in the future.

Prof. Price: “We discovered that thunderstorms are a major mechanism in the formation of cirrus clouds, and that lightning activity can account for over 70% of the changes in the quantity of cirrus clouds in the world. Thunderstorms act as an enormous ”vacuum cleaner”, lifting moisture from the surface of the planet, especially above oceans and forests, to higher levels of the atmosphere. There, at an altitude of about 10km, this moisture turns into ice crystals that form the cirrus clouds.”

...

https://scienceblog.com/539613/rise-in-global-thunderstorm-activity-might-increase-the-quantity-of-wispy-cirrus-clouds-accelerating-global-warming/

[kassy]

How rising water vapour in the atmosphere is amplifying warming and making extreme weather worse


This year’s string of record-breaking disasters – from deadly wildfires and catastrophic floods to record-high ocean temperatures and record-low sea ice in Antarctica – seems like an acceleration of human-induced climate change.

And it is. But not only because greenhouse gas emissions continue to rise. What we are also observing is the long-predicted water vapour feedback within the climate system.

Since the late 1800s, global average surface temperatures have increased by about 1.1°C, driven by human activities, most notably the burning of fossil fuels which adds greenhouse gases (carbon dioxide and methane) to the atmosphere.

As the atmosphere warms, it can hold more moisture in the form of water vapour, which is also a greenhouse gas. This in turn amplifies the warming caused by our emissions of other greenhouse gases.

Some people mistakenly believe water vapour is a driver of Earth’s current warming. But as I explain below, water vapour is part of Earth’s hydrological cycle and plays an important role in the natural greenhouse effect. Its rise is a consequence of the atmospheric warming caused by our emissions arising especially from burning fossil fuels.

Water vapour: the other greenhouse gas
For every degree Celsius in warming, the water-holding capacity of the atmosphere increases by about 7%. Record-high sea temperatures ensure there is more moisture (in the form of water vapour) in the atmosphere, by an estimated 5-15% compared to before the 1970s, when global temperature rise began in earnest.

Water vapour is a powerful greenhouse gas. Since the 1970s, its rise likely increased global heating by an amount comparable to that from rising carbon dioxide. We are now seeing the consequences.

In many ways, water vapour is the most important greenhouse gas as it makes Earth habitable. But human-induced climate change is primarily caused by increases in the long-lived greenhouse gases carbon dioxide, nitrous oxide, methane and chlorofluorocarbons (CFCs).

As a general rule, any molecule with three or more atoms is a greenhouse gas, owing to the way the atoms can vibrate and rotate within the molecule. A greenhouse gas absorbs and re-emits thermal (infrared) radiation and has a blanketing effect.

Clouds have a blanketing effect similar to that of greenhouse gases but they are also bright reflectors of solar radiation and act to cool the surface by day. In the current climate, for average all-sky conditions, water vapour is estimated to account for 50% of the total greenhouse effect, carbon dioxide 19%, ozone 4% and other gases 3%. Clouds make up about a quarter of the greenhouse effect.

Why is water vapour different?
The main greenhouse gases – carbon dioxide, methane, nitrous oxide and ozone – don’t condense and precipitate. Water vapour does, which means its lifetime in the atmosphere is much shorter, by orders of magnitude, compared to other greenhouse gases.

On average, water vapour only lasts nine days, while carbon dioxide stays in the atmosphere for centuries or even millennia, methane lasts for a decade or two and nitrous oxide a century. These gases serve as the backbone of atmospheric heating, and the resulting rise in temperature is what enables the observed increase in water vapour levels.

The rise in carbon dioxide doesn’t depend on weather. It comes primarily from the burning of fossil fuels. Atmospheric carbon dioxide has increased from pre-industrial levels of 280ppmv to 420ppmv (an increase of 50%) and about half of that increase has happened since 1985.

This accounts for about 75% of the anthropogenic heating from long-lived greenhouse gases. The rest of human-induced atmospheric warming mainly comes from methane and nitrous oxide, with offsets from pollution aerosols.

The extra heating from water vapour has been on a par with that from increased carbon dioxide since the 1970s.

...

Water is the air conditioner of the planet. It not only keeps the surface cooler (albeit at the expense of making it moister) but rain also washes a lot of pollution out of the atmosphere to everyone’s benefit.

Precipitation is vitally important. It nourishes vegetation and supports various ecosystems as long as the rate is moderate. But as the climate warms, higher moisture levels increase the potential for heavier rainfall and the risk of flooding.

Moreover, the latent energy that went into evaporation is returned to the atmosphere, adding to heating and causing air to rise, invigorating storms and making weather extremes greater and less manageable.

These changes mean that where it is not raining, drought and wildfire risk increase, but where it is raining, it pours.

https://theconversation.com/how-rising-water-vapour-in-the-atmosphere-is-amplifying-warming-and-making-extreme-weather-worse-213347

[kassy]

Luminous ‘mother-of-pearl’ clouds explain why climate models miss so much Arctic and Antarctic warming


Our planet has warmed by about 1.2°C since 1850. But this warming is not uniform. Warming at the poles, especially the Arctic, has been three to four times faster than the rest of the globe. It’s a phenomenon known as “polar amplification”.

Climate models simulate this effect, but when tested against the past 40 years of warming, these models fall short. The situation is even worse when it comes to modelling past climates with very high levels of greenhouse gases.

This is a problem because these are the same models used to project into the future and forecast how the climate will change. They are likely to underestimate what will happen later this century, including risks such as ice sheet melting or permafrost thawing.

In our new research published today in Nature Geoscience we used a high-resolution model of the atmosphere that includes the stratosphere. We found a special type of cloud appears over polar regions when greenhouse gas concentrations are very high. The role of this type of cloud has been overlooked so far. This is one of the reasons why our models are too cold at the poles.

Back to the future
Looking into past climates can give us glimpses of possible futures for a range of extreme conditions. For us, this means we can use Earth’s history to find out how well our climate models perform. We can test our models by simulating episodes in the past when Earth was much warmer. The advantage of this is that we have temperature reconstructions for these episodes to evaluate the models, as opposed to the future, for which measurements are not available.

If we go back 50 million years or so, our planet was very hot. Carbon dioxide (CO₂) concentrations ranged between 900 and 1,900 parts per million (ppm), compared with 415 ppm today. Methane (CH₄) concentrations were likely also much higher.

Canada’s arctic archipelago was covered in lush rainforests inhabited by alligators, turtles, lizards and mammals.

For these plants and animals to survive, conditions must have been warm and ice-free year-round. Indeed, surface ocean temperatures exceeded 20°C near the north pole (at about 87°N) and 25°C in the Southern Ocean (at about 67°S).

This period called the early Eocene is a perfect test bed for our models, because it was globally very warm, and the poles were even warmer, meaning it was a climate with extreme polar amplification. In addition, the Eocene is recent enough for temperature reconstructions to be available.

But as it turns out, the models fail again. They are much too cold at high latitudes. What are our models missing?

Polar stratospheric clouds
In 1992 American paleoclimatologist Lisa Sloan suggested polar stratospheric clouds might have caused extreme warming at high latitudes in the past.

These clouds are a rare and beautiful sight today. They are also called nacreous or mother-of-pearl clouds for their vivid and sometimes luminous colours.

They form at very high altitudes (in the stratosphere) and at very low temperatures (over the poles). In the present day climate, they appear mainly over Antarctica, but have also been observed during winter months over Scotland, Scandinavia and Alaska, at times when the stratosphere was particularly cold.

Just like greenhouse gases, they absorb infrared radiation emitted by the Earth’s surface and re-emit a portion of this energy back to the surface. This suggests polar stratospheric clouds could be one of the missing puzzle pieces.

They warm the surface. And their effect could be significant, especially in winter, when the sun does not rise. But they are difficult to simulate in a climate model, so most models ignore them. This omission could explain why climate models miss some of the polar warming, because they miss a process that warms the poles.

Three decades after Sloan’s paper, a few atmosphere models are finally complex enough to allow us to test her hypothesis. In our research we use one of them and find that under certain conditions, the additional warming due to these polar stratospheric clouds exceeds 7°C during the winter months. This significantly reduces the gap between climate models and temperature evidence from the early Eocene. Sloan was right.

Implications for future projections
Our research explains why climate models don’t work so well for past climates when greenhouse gas levels were much higher than they are today. But what about the future? Should we be concerned?

There is some good news. While polar stratospheric clouds do warm the poles, they won’t be as common in the future as they were in the distant past, even if both CO₂ and CH₄ reach very high levels.

This is due to another difference between the Eocene and today: the position of continents and mountains, which were different back then and which also influence the formation of polar stratospheric clouds. So even if we hit early Eocene levels of CH₄ and CO₂ in the future, we would expect less polar stratospheric cloud to be formed. This suggests the standard climate models are better at predicting the future than the past.

...

https://theconversation.com/luminous-mother-of-pearl-clouds-explain-why-climate-models-miss-so-much-arctic-and-antarctic-warming-217066

Early Eocene low orography and high methane enhance Arctic warming via polar stratospheric clouds

Abstract
Proxy data suggest that the early Eocene (∼56–47.8 million years ago) was characterized by a much weaker equator-to-pole temperature gradient than today. However, general circulation models consistently underestimate high-latitude temperatures indicated by proxy records, suggesting that they may miss important processes. Previous studies hypothesized that wintertime polar stratospheric clouds may have played an important role in Arctic warming through greenhouse forcing, but these studies did not consider the effects of atmospheric chemistry or the early Eocene topography. Here we examine these factors using a high-top atmospheric model with interactive chemistry. The lower orography in the low- to mid-latitude Northern Hemisphere early Eocene weakens the stratospheric circulation which, in combination with sufficiently high methane concentrations, leads to a substantial increase in polar stratospheric clouds in the Arctic winter. Furthermore, an increase in early Eocene polar stratospheric clouds due to a 16- to 64-fold higher than pre-industrial methane concentration results in a radiative forcing larger than the direct greenhouse effect from the methane itself. This polar stratospheric cloud-induced radiative forcing could cause up to 7.4 K of Arctic surface warming. These results point to the potential for nonlinear interactions between individual forcings.

https://www.nature.com/articles/s41561-023-01298-w

[kassy]

Future floods: Global warming intensifies heavy rain -- even more than expected

The intensity and frequency of extreme rainfall increases exponentially with global warming, a new study finds. The analysis shows that state-of-the-art climate models significantly underestimate how much extreme rainfall increases under global warming -- meaning that extreme rainfall could increase quicker than climate models suggest.

...

While most land-areas exhibit increases in both the intensity and frequency of extremes, stronger increases are typically found across tropical regions, according to the study. Significant changes most often occur across the tropics and high-latitudes, like in Southeast Asia or Northern Canada. The fact that these changes follow the Clausius-Clapeyron relation underpins the fact that thermodynamics, i.e. temperature and not dynamics, i.e. winds, dominate the global change of extreme rainfall events. "The good news is that this makes it easier to predict the future of extreme rainfall. The bad news is: It will get worse, if we keep pushing up global temperatures by emitting greenhouse gases," Anders Levermann adds.

https://www.sciencedaily.com/releases/2023/11/231127132446.htm

[kassy]

Study links changes in global water cycle to higher temperatures

A new study takes an important step toward reconstructing a global history of water over the past 2,000 years. Using geologic and biologic evidence preserved in natural archives -- including 759 different paleoclimate records from globally distributed corals, trees, ice, cave formations and sediments -- the researchers showed that the global water cycle has changed during periods of higher and lower temperatures in the recent past.

...

"The global water cycle is intimately linked to global temperature," said Konecky, an assistant professor of earth, environmental and planetary sciences in Arts & Sciences at Washington University and lead author of the new study in Nature Geoscience.

"We found that during periods of time when temperature is changing at a global scale, we also see changes in the way that water moves around the planet," she said.

The water cycle is complex, and rainfall in particular has geographic variations that are much more drastic than air temperature. This has made it difficult for scientists to evaluate how rainfall has changed over the past 2,000 years.

"We decided to start with water isotope records because they reflect holistic signals and because they're recorded in all kinds of different natural archives," Konecky said. "This is a first step toward reconstructing drought or rainfall patterns at the global scale during the past 2,000 years."

An intertwined cycle

The global water cycle is vast and intertwined. Water evaporates from the surface of the Earth, rises into the atmosphere, cools and condenses into rain or snow in clouds, and falls again to the surface as precipitation. Each water molecule that is part of the cycle has a certain isotopic 'fingerprint,' or composition, which reflects small variations in the atomic weight of the oxygen and hydrogen atoms that comprise the molecule. So, individual water molecules can be heavier or lighter.

With this new study, the scientists found that when global temperature is higher, rain and other environmental waters become more isotopically heavy. The researchers interpreted these isotopic changes and determined their timeline by synthesizing data from across a wide variety of natural archive sources from the past 2,000 years of Earth history.

...

Global scale relationships between temperature and the isotopic composition of certain environmental waters, like seawater and glacial ice, have long been recognized as the planet moves in and out of ice age cycles. Local scale relationships with temperature on timescales of minutes to months are also well established.

But this study provides the first evidence that temperature and the isotopic composition of environmental waters go hand in hand at timescales in between these two -- that is, over decades to centuries.

It's a rapid adjustment, Konecky said. "As the planet warms and cools, it affects the behavior of water as it leaves the oceans and the vigor of its motions through the atmosphere," she said. "The isotopic signals in these waters are very responsive to temperature changes."

The scientists found that global mean surface temperature exerted a coherent influence on the isotopic composition of global precipitation and "meteoric water" (water in lakes, rivers and ice melts) throughout the past 2,000 years. The changes they observed were driven by global ocean evaporation and condensation processes, with lower values during the period of time known as the Little Ice Age (1450-1850) and higher values after the onset of human-caused climate warming starting around 1850.

When it comes to the specific impact of these changes on future rainfall and water availability, it is too early to predict who will win and who will lose. But this study's data from the last 2,000 years suggest that more water cycle changes are likely as global temperatures continue to increase. June, July and August 2023 were the hottest months on record for our planet.

"The way water behaves when it leaves the oceans and moves around the atmosphere and rains out -- that behavior is strongly impacted by changes in atmospheric temperature," Konecky said.

https://www.sciencedaily.com/releases/2023/11/231102134954.htm


Abstract of the paper since the summery given above is very general:

Abstract
The response of the global water cycle to changes in global surface temperature remains an outstanding question in future climate projections and in past climate reconstructions. The stable hydrogen and oxygen isotope compositions of precipitation (δprecip), meteoric water (δMW) and seawater (δSW) integrate processes from microphysical to global scales and thus are uniquely positioned to track global hydroclimate variations. Here we evaluate global hydroclimate during the past 2,000 years using a globally distributed compilation of proxies for δprecip, δMW and δSW. We show that global mean surface temperature exerted a coherent influence on global δprecip and δMW throughout the past two millennia, driven by global ocean evaporation and condensation processes, with lower values during the Little Ice Age (1450–1850) and higher values after the onset of anthropogenic warming (~1850). The Pacific Walker Circulation is a predominant source of regional variability, particularly since 1850. Our results demonstrate rapid adjustments in global precipitation and atmospheric circulation patterns—within decades—as the planet warms and cools.

https://www.nature.com/articles/s41561-023-01291-3

paywalled

[kassy]

High-resolution lidar sees birth zone of cloud droplets


A team led by atmospheric scientists at the U.S. Department of Energy's Brookhaven National Laboratory has demonstrated the first-ever remote observations of the fine-scale structure at the base of clouds. The results, just published in the Nature publication NPJ Climate and Atmospheric Science, show that the air-cloud interface is not a perfect boundary but rather is a transition zone where aerosol particles suspended in Earth's atmosphere give rise to the droplets that ultimately form clouds.

"We are interested in this 'droplet activation zone,' where most cloud droplets are initially formed at the cloud base, because the number of droplets formed there will affect the later stages and properties of the cloud -- including how much sunlight a cloud reflects and the likelihood of precipitation," said Brookhaven atmospheric scientist Fan Yang, the first author on the paper.

"If there are more aerosols in the atmosphere, clouds tend to have more droplets, but the droplets will each be smaller, which means they can reflect more sunlight," Yang said. "This might help to cool our warming Earth," he noted.

But to accurately predict the impacts of these aerosol-cloud interactions on the climate system, scientists need a way to measure cloud droplet number concentrations -- without having to fly up into lots of clouds to collect samples.

"This remains one of the biggest challenges in our field," Yang said.

The new remote-sensing measurements and method provide a novel way to estimate droplet concentration, which will enable scientists to gain insight into how changes in atmospheric aerosol levels could affect clouds and climate.

Seeing clouds in finer detail

Atmospheric lidars -- which send laser beams into the atmosphere and measure the signals of light backscattered from molecules, aerosols, and cloud droplets in the atmosphere -- have been widely used to measure the distance to the cloud base. But traditional lidars can't resolve detailed structures within the cloud base because they typically have a resolution of 10 meters or more.

"Ten meters is like the height of a building," said Yang, noting the ability of this scale to detect large objects. "But to know how many floors or windows that building has, you'd need much finer resolution."

To see details within the cloud base, the Brookhaven team worked with colleagues at Stevens Institute of Technology (SIT) and Raymetrics S.A. to build a new kind of lidar. Their device, described in an earlier publication, is a time-gated, time-correlated, single-photon counting lidar (T2 lidar) with a resolution down to 10 centimeters. That's two orders of magnitude higher resolution than traditional atmospheric lidars.

"With such a high resolution, the T2 lidar observations reveal the transition zone where aerosol particles absorb water vapor to be transformed into cloud droplets," Yang said.

"We used our unprecedented fine-scale T2 observations of the cloud base region to develop a theoretical model to estimate cloud droplet concentration based on T2-measured backscatter signals," he added.

One unique feature of the T2 lidar is the application of the time-gating technique -- forcing the detector to open its "eye" to make measurements in a narrow observational window in the atmosphere.

"This time gating allows us to 'look' at a specific region of interest within the cloud. This is different from a conventional lidar, where the lidar's 'eye' is generally open, being ready to capture back-scattered photons nearly all the time," Yang said.

By setting the time delay between the T2 lidar's laser pulse and the eye opening to different time intervals, the scientists can sample signals at different regions through the cloud.

The device also has a very high repetition rate, firing 20,000 laser pulses per second.

"We can learn about cloud properties from how the back-scattered signals are distributed within the observational window," Yang said.

and more:
https://www.sciencedaily.com/releases/2024/04/240424111527.htm

[kassy]

And then there is this:

How light can vaporize water without the need for heat


It's the most fundamental of processes -- the evaporation of water from the surfaces of oceans and lakes, the burning off of fog in the morning sun, and the drying of briny ponds that leaves solid salt behind. Evaporation is all around us, and humans have been observing it and making use of it for as long as we have existed.

And yet, it turns out, we've been missing a major part of the picture all along.

In a series of painstakingly precise experiments, a team of researchers at MIT has demonstrated that heat isn't alone in causing water to evaporate. Light, striking the water's surface where air and water meet, can break water molecules away and float them into the air, causing evaporation in the absence of any source of heat.

The astonishing new discovery could have a wide range of significant implications. It could help explain mysterious measurements over the years of how sunlight affects clouds, and therefore affect calculations of the effects of climate change on cloud cover and precipitation. It could also lead to new ways of designing industrial processes such as solar-powered desalination or drying of materials.

...

A newfound phenomenon

The new work builds on research reported last year, which described this new "photomolecular effect" but only under very specialized conditions: on the surface of specially prepared hydrogels soaked with water. In the new study, the researchers demonstrate that the hydrogel is not necessary for the process; it occurs at any water surface exposed to light, whether it's a flat surface like a body of water or a curved surface like a droplet of cloud vapor.

Because the effect was so unexpected, the team worked to prove its existence with as many different lines of evidence as possible. In this study, they report 14 different kinds of tests and measurements they carried out to establish that water was indeed evaporating -- that is, molecules of water were being knocked loose from the water's surface and wafted into the air -- due to the light alone, not by heat, which was long assumed to be the only mechanism involved.

One key indicator, which showed up consistently in four different kinds of experiments under different conditions, was that as the water began to evaporate from a test container under visible light, the air temperature measured above the water's surface cooled down and then leveled off, showing that thermal energy was not the driving force behind the effect.

Other key indicators that showed up included the way the evaporation effect varied depending on the angle of the light, the exact color of the light, and its polarization. None of these varying characteristics should happen because at these wavelengths, water hardly absorbs light at all -- and yet the researchers observed them.

The effect is strongest when light hits the water surface at an angle of 45 degrees. It is also strongest with a certain type of polarization, called transverse magnetic tion. And it peaks in green light -- which, oddly, is the color for which water is most transparent and thus interacts the least.

Chen and his co-researchers have proposed a physical mechanism that can explain the angle and polarization dependence of the effect, showing that the photons of light can impart a net force on water molecules at the water surface that is sufficient to knock them loose from the body of water. But they cannot yet account for the color dependence, which they say will require further study.

...

https://www.sciencedaily.com/releases/2024/04/240424160652.htm

[kassy]

The cleanest air in the world is at Tasmania's Kennaook/Cape Grim. It's helping solve a climate puzzle

In short: For nearly five decades, the Kennaook/Cape Grim air-monitoring station on Tasmania's north-west tip has been pivotal in tracking human-induced changes to the global atmosphere.

Australian and US scientists have teamed up to analyse "super-cooled" liquid clouds over the Southern Ocean, which are skewing climate models because of a lack of data.

What's next: The "CAPE-K" project will run until late next year, with the aim of improving our ability to forecast long-term changes to the climate.


...

Twenty-five kilometres up the coast from his property is one of the world's three "premier" stations that monitor baseline air pollution.

Established in 1976, the Kennaook/Cape Grim facility can accurately measure changes in the global atmosphere without the interference of local contamination.

"Air here under baseline conditions is very, very clean," CSIRO atmospheric scientist Melita Keywood said.

...

On a rooftop deck overlooking the rugged coastline, the facility's officer-in-charge, Sarah Prior, is checking the direction of the wind.

When it comes from the west or south-west, it's travelled thousands of kilometres across the Southern Ocean, avoiding the smog and dust of cities or landmasses.

"At that time … we are measuring the lowest levels of pollution that you'll see," Ms Prior said.

Scientists at Kennaook/Cape Grim describe it as "baseline" air — the cleanest on the planet.

Once it's captured, the air is siphoned into a laboratory where high-tech machines analyse its chemical and physical properties.

"In a nutshell, we measure our greenhouse gases and ozone-depleting substances," Ms Prior said.

"We also measure the aerosols and reactive gases, and we measure radon as well."

Air quality readings taken over 50 years
For almost five decades, the station has been pivotal in tracking the impact of human activity on the atmosphere.

When the first readings were taken at Kennaook/Cape Grim, carbon dioxide levels were just below 330 parts per million.

These days they are at more than 417 parts per million, an increase of almost 25 per cent since the 1970s.

The increase in carbon dioxide, as well as other greenhouse gases and chemicals, is reflected in Kennaook/Cape Grim's "archive" of air.

Every two months, staff at the facility don protective gear to cryogenically fill a high-pressure tank with thousands of litres of baseline air.

It's a process that's been undertaken since 1978, with about 250 canisters now held in the air archive at a CSIRO facility in Melbourne.

"By filling multiple cylinders per year over many years, we can go back and actually analyse old air when we get new instrumental techniques," Paul Krummel, from CSIRO's greenhouse gas and ozone-depleting substances program, said.

Climate project tries to unravel cloud mystery
While scientists have a clear picture of the past, the computations used to forecast future atmospheric changes are far less precise.

It is the reason Kennaook/Cape Grim is now hosting an important international climate project known as "CAPE-K".

CAPE-K stands for Cloud and Precipitation Experiment at Kennaook.

It is a collaboration between the Bureau of Meteorology, the CSIRO and US Department of Energy.

"Whenever we talk about climate change and climate models, and predicting future climate, there's always this element of uncertainty," the Department of Energy's Heath Powers said.

"And almost all of that uncertainty in climate models has to do with our ability — or our lack of ability — to represent clouds very, very well."

Most climate models assume that when clouds form in freezing conditions, ice crystals develop inside them.

But for the ice to form, there usually needs to be dust or pollution in the air — something that's not prevalent over the Southern Ocean.

The purity of the air is the reason why many of the clouds in the Southern Ocean remain in a "super-cooled liquid" state, even when the temperature falls below zero degrees Celsius.

These liquid clouds reflect more sunlight back into space than ice clouds, which means less heat is absorbed by the ocean.

But this phenomenon is not accurately incorporated into current climate calculations.

"To make these predictions much better, we need to go out and measure the types of clouds that we're trying to represent," Mr Powers said.

...

https://www.abc.net.au/news/2024-05-05/tas-kennaook-cape-grim-pollution-monitor-station-cloud-project/103793926

[kassy]

Supercharged thunderstorms: have we underestimated how climate change drives extreme rain and floods?

In media articles about unprecedented flooding, you’ll often come across the statement that for every 1°C of warming, the atmosphere can hold about 7% more moisture.

This figure comes from research undertaken by the French engineer Sadi Carnot and published 200 years ago this year.

We now know there’s more to the story. Yes, a hotter atmosphere has the capacity to hold more moisture. But the condensation of water vapour to make rain droplets releases heat. This, in turn, can fuel stronger convection in thunderstorms, which can then dump substantially more rain.

This means that the intensity of extreme rainfall could increase by much more than 7% per degree of warming. What we’re seeing is that thunderstorms can likely dump about double or triple that rate – around 14–21% more rain for each degree of warming.

Thunderstorms are a major cause of extreme flooding around the world, contributing to Brazil’s disastrous floods, which have submerged hundreds of towns, and Dubai’s flooded airport and roads.

For Australia, we helped develop a comprehensive review of the latest climate science to guide preparedness for future floods. This showed the increase per degree of global warming was about 7–28% for hourly or shorter duration extreme rain, and 2–15% for daily or longer extreme rain. This is much higher than figures in the existing flood planning standards recommending a general increase of 5% per degree of warming.

...

Climate change pumps up extreme flood risk factors
The latest report from the Intergovernmental Panel on Climate Change (IPCC) states that:

frequency and intensity of heavy precipitation events have increased since the 1950s over most land areas for which observational data are sufficient for trend analysis (high confidence), and human-induced climate change is likely the main driver

This increase is particularly clear in short-duration extreme rains, such as those caused by thunderstorms.

Why? In part, it’s because of the 7% figure – warmer air is able to hold more water vapour.

But that doesn’t explain everything. There’s something else going on. Condensation produces heat. So as water vapour turns into droplets, more heat becomes available, and hot air rises by convection. In thunderstorms, more heat fuels stronger convection, where warm, moisture-laden air is driven up high.

This explains why thunderstorms can now drive such extreme rainfall in our warming world. As water vapour condenses to make rain, it also makes heat, supercharging storms.

We are seeing these very rapid rates of rainfall increase in recent decades in Australia.

Daily rainfall associated with thunderstorms has increased much more than the 7% figure would suggest – about 2-3 times more.

Hourly rainfall extremes have also increased in intensity at similar rates.

What about very sudden, extreme rains? Here, the rate of increase could potentially be even larger. One recent study examined extreme rain for periods shorter than one hour near Sydney, suggesting about a 40% increase or more over the past 20 years.

Rapid trends in extreme rainfall intensity are also clear in other lines of evidence, such as fine-resolution modelling.

To model complex climate systems, we need the grunt of supercomputers. But even so, many of our models for climate projections don’t drill down to grid resolutions smaller than about 100 kilometres.

While this can work well for large-scale climate modelling, it’s not suitable for directly simulating thunderstorms. That’s because the convection processes needed to make thunderstorms form happen on much smaller scales than this.

There’s now a concerted effort underway to perform more model simulations at very fine scales, so we can improve the modelling of convection.

Recent results from these very fine scale models for Europe suggest convection will play a more important role in triggering extreme rainfall including in combined storms, such as thunderstorms mingling with low pressure systems and other combinations.

This matches Australian observations, with a trend towards increased rain from thunderstorms combining with other storm types such as cold fronts and cyclones (including low-pressure systems in southern Australia).

...

https://theconversation.com/supercharged-thunderstorms-have-we-underestimated-how-climate-change-drives-extreme-rain-and-floods-228896