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How clouds will amplify global warming by reflecting less heat

A new study warns that global temperatures are likely to increase, partly due to clouds reflecting less solar radiation

Clouds pass over skyscrapers at Circular Quay at sunset during a lockdown to curb the spread of a coronavirus disease (COVID-19) outbreak in Sydney, Australia, July 15, 2021. (REUTERS)

Global temperatures are likely to increase by more than 3 degrees Celsius -- which is double the UN climate targets -- partly due to clouds reflecting less solar radiation and enhancing the greenhouse effect, according to a new study.

The research, published this week in the journal Proceedings of the National Academy of Sciences, is the strongest evidence so far that clouds will amplify global heating over the long-term, further amplfying climate change.

Also read: Human activity, man-made emissions behind nearly all global warming

Scientists at Imperial College London and the University of East Anglia in the UK employed a new approach to analyse satellite measurements of Earth's cloud cover.

Their findings suggest that at double atmospheric carbon dioxide (CO2) concentrations above pre-industrial levels, the climate is unlikely to warm below 2 degrees Celsius, and is more likely on average to warm more than 3 degrees Celsius.

Pre-industrial CO2 levels were around 280 parts per million (ppm), but current levels are approaching 420 ppm, and could approach double the pre-industrial amount by mid-century if significant emissions cuts are not made. The amount of climate warming predicted from a doubling of pre-industrial CO2 levels is known as the "climate sensitivity" -- which is a measure of how strongly our climate will react to such a change, a news release explains.

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

Dark clouds looming over La Defense business dictrict are seen from the roof of the Arc de Triomphe in Paris on July 12, 2021. The researchers noted that low clouds tend to have a cooling effect, as they block the sun from reaching the ground. High clouds, however, have a warming effect.
Dark clouds looming over La Defense business dictrict are seen from the roof of the Arc de Triomphe in Paris on July 12, 2021. The researchers noted that low clouds tend to have a cooling effect, as they block the sun from reaching the ground. High clouds, however, have a warming effect. (AFP)

"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 degree Celsius of global warming,” the study's co-author Paulo Ceppi, from Imperial College London, explains in the release.

"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," Ceppi said.

The researchers noted that 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, the release explains.

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.

In this Tuesday, Sept. 15, 2020 file photo, the sun rises behind a wind turbine in Frankfurt, Germany. The results of this study also suggest that a doubling of CO2 concentrations will lead to around 3.2 degrees Celsius of warming.
In this Tuesday, Sept. 15, 2020 file photo, the sun rises behind a wind turbine in Frankfurt, Germany. The results of this study also suggest that a doubling of CO2 concentrations will lead to around 3.2 degrees Celsius of warming. (AP)

The researchers developed a new method to quantify the relationship between state-of-the-art global satellite observations of clouds, and the associated temperature, humidity and wind conditions. They found it was very likely (a probability of more than 97.5 per cent) 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 degrees Celsius 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.

"Over the last few years, there's been a growing amount of evidence that clouds probably have an amplifying effect on global warming,” co-author Peer Nowack, from the University of East Anglia, says in the release. “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,” Nowack added.

(With inputs from PTI)

Also read: Global warming is melting the world's glaciers at an alarming rate

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