{"id":2317,"date":"2023-03-08T13:43:53","date_gmt":"2023-03-08T13:43:53","guid":{"rendered":"https:\/\/horizon.peachpuff-wolverine-566518.hostingersite.com\/?p=2317"},"modified":"2023-03-08T13:44:44","modified_gmt":"2023-03-08T13:44:44","slug":"clouds-in-the-sky-provide-new-clues-to-predicting-climate-change","status":"publish","type":"post","link":"https:\/\/scienceblog.com\/horizon\/2317\/clouds-in-the-sky-provide-new-clues-to-predicting-climate-change\/","title":{"rendered":"Clouds in the sky provide new clues to predicting climate change"},"content":{"rendered":"

While barely being given a second thought by most people, the masses of condensed water vapour floating in the atmosphere play a big role in global warming.<\/p>\n

By<\/em>\u00a0\u00a0MICHAEL ALLEN<\/p>\n

Predicting how much Earth\u2019s climate will warm is vital to helping humankind prepare for the future. That in turn requires tackling a prime source of uncertainty in forecasting global warming: clouds.<\/p>\n

Some clouds contribute to cooling by reflecting part of the Sun\u2019s energy back into space. Others contribute to warming by acting like a blanket and trapping some of the energy of Earth\u2019s surface, amplifying the greenhouse effect.<\/p>\n

Puzzle pieces<\/strong><\/p>\n

\u2018Clouds interact very strongly with climate,\u2019 said Dr Sandrine Bony, a climatologist and director of research at the French National Centre for Scientific Research (CNRS) in Paris.<\/p>\n

They influence the structure of the atmosphere, impacting everything from temperature and humidity to atmospheric circulations.<\/p>\n

And in turn the climate influences where and what types of clouds form, according to Bony, a lead author of the Nobel Peace Prize-winning assessment report in 2007 by the United Nations Intergovernmental Panel on Climate Change.<\/p>\n

So many processes and feedback loops can affect climate change that it\u2019s helpful to break down the issue into smaller parts.<\/p>\n

\u2018Every time we manage to better understand one of the pieces, we decrease the uncertainty of the whole problem,\u2019 said Bony, who coordinated the EU-funded\u00a0EUREC4<\/sup>A<\/a>\u00a0project that ended last year.<\/p>\n

A number of years ago, Bony and her colleagues discovered that small, fluffy clouds common in trade wind regions cause some of the largest levels of uncertainty in climate models. These clouds are known as trade cumulus.<\/p>\n

While trade cumulus clouds are small and relatively unspectacular, they are numerous and very widely found in the tropics, according to Bony. Because there are so many of these clouds, what happens to them potentially has a huge impact on climate.<\/p>\n

EUREC4<\/sup>A used drones, aircraft and satellites to observe trade cumulus clouds and their interactions with the atmosphere over the western Atlantic Ocean, near Barbados.<\/p>\n

Many models assume that the structure and number of these clouds will change significantly as the global temperature warms, leading to possible feedback loops that amplify or dampen climate change. The models that project a strong reduction in such clouds as temperatures rise tend to predict a higher degree of global warming.<\/p>\n

Good news<\/strong><\/p>\n

But Bony and her colleagues discovered that trade cumulus clouds change much less than expected as the atmosphere warms.<\/p>\n

\u2018In a way, it is good news because a process that we thought could be responsible for a large amplification of global warming does not seem to exist,\u2019 she said.<\/p>\n

More importantly, it means that climatologists can now use models that more accurately represent the behaviour of these clouds when predicting the effect of climate change.<\/p>\n

Reducing this element of uncertainty in forecasts of the global extent of warming will make predictions of local impacts such as heatwaves in Europe more precise, according to Bony.<\/p>\n

\u2018The increase in the frequency of heatwaves very much depends on the magnitude of global warming,\u2019 she said. \u2018And the magnitude of global warming depends very much on the response of clouds.\u2019<\/p>\n

Water and ice<\/strong><\/p>\n

Meanwhile, Professor Trude Storelvmo, an atmospheric scientist at the University of Oslo in Norway, has been exploring the processes inside a different type of cloud \u2013 mixed-phased clouds \u2013 to help improve climate models.<\/p>\n

She is fascinated by how processes in clouds that occur on a tiny, micrometre scale can have such a big influence on global-scale atmospheric and climate processes.<\/p>\n

Mixed-phase clouds contain both liquid water and ice and are responsible for the majority of rainfall across the globe. In recent years, it has become clear that they also play an important role in climate change.<\/p>\n

Storelvmo coordinated the EU-funded\u00a0MC2<\/a>\u00a0project, which ran for five years until last month and unearthed new details about how mixed-phase clouds react to higher temperatures. The results highlight the urgency of transitioning to a low-carbon society.<\/p>\n

The more liquid water that mixed-phased clouds contain, the more reflective they are. And by reflecting more radiation from the sun away from the Earth, they cool the atmosphere.<\/p>\n

\u2018As the atmosphere warms, these clouds tend to shift away from ice and towards liquid,\u2019 said Storelvmo. \u2018What happens then is the clouds also become more reflective and they have a stronger cooling effect.\u2019<\/p>\n

Rude awakening<\/strong><\/p>\n

But some years ago, Storelvmo and colleagues discovered that most global climate models overestimate this effect. MC2 flew balloons into mixed-phase clouds and used remote sensing data from satellites to probe their structure and composition.<\/p>\n

The researchers discovered that current climate models tend to make the mix of water and ice in mixed-phase clouds more uniform and less complex than in real clouds, leading to overestimations of the amount of ice in the clouds.<\/p>\n

Because these model clouds have more ice to lose, when simulations warm them the shift in reflectiveness is greater than in real clouds, according to Storelvmo. This means the models overestimate the dampening effect that mixed-phase clouds have on climate change.<\/p>\n

When the team plugged the more realistic cloud data into climate models and subjected it to simulated warming, they made another important finding: the increase in the reflectiveness of mixed-phased clouds weakens with warming.<\/p>\n

While with moderate warming the dampening effect on higher temperatures is quite strong, this is no longer the case as warming intensifies.<\/p>\n

There comes a point when the ice in the cloud has all melted and the cooling effect weakens \u2013 and then completely vanishes. Exactly when this starts to happen is a question for future research.<\/p>\n

But, according to Storelvmo, this reinforces the need for urgent reductions in greenhouse-gas emissions.<\/p>\n

\u2018Our findings suggest that if we just let greenhouse-gas emissions continue, it won\u2019t just be a linear and gradual warming\u00a0\u2013 there could be a rapidly accelerating warming when you get to a certain point,\u2019 she said. \u2018We really need to avoid reaching that point at all costs.\u2019<\/p>\n

As new findings on clouds such as these are integrated into models, climate predictions used by policymakers will become more refined.<\/p>\n

Research in this article was funded via the EU\u2019s European Research Council (ERC). The article was originally published\u202fin <\/em>Horizon<\/em><\/a>, the EU Research and Innovation Magazine.\u00a0<\/em><\/p>\n

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