Why global warming slowed down: the answer’s in the clouds

Cloudy skies could explain the slowdown in global warming at the turn of the 21st century.

Clouds could explain a ‘pause’ in global warming. Picture: AAP

Cloudy skies could explain the slowdown in global warming or “pause” at the turn of the 21st century, according to new research by Russian scientists.

Clouds reflect back the heat of the sun so less clouds means higher surface temperatures on land.

More clouds mean lower temperatures.

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Researchers at St Petersburg University studied international data on cloud cover between 1983 and 2009.

The results were sufficient to claim that the level and variation in cloud cover over that period “can explain not only the linear trend of global temperature, but also a certain interannual variability”.

The scientists, led by O M Pokrovsky, said the impact of clouds had been underestimated and could no longer be ignored.

A better understanding was needed on how and why clouds formed.

The Russian scientists said a simple linear regression model suggests that a 1 per cent increase in global low cloud cover corresponds to a global temperature drop of around 0.06 degrees Celsius and vice versa.

Professor Pokrovsky said changes in cloud cover matched temperature trends over the study period including the slowdown in temperature rises at the beginning of the 21st century.

Cloud cover is one of serval explanations for the “hiatus” in global warming. Others include changes in ocean dynamics and more particles in the atmosphere from volcanoes and air pollution.

Cloud cover is one of serval explanations for the “hiatus” in global warming.

Some scientists claim the pause did not actually happen.

The Russian researchers said knowledge about the mechanisms of cloud formation and evolution was obviously insufficient, and the methods and parameters used in climate models were inaccurate.

“The fact that simultaneously with an increase in ocean temperature, which entails an increase in evaporation from the water surface, a decrease in cloudiness and, above all, over the oceans, requires a critical analysis of the existing ideas about the mechanisms of cloud formation at different latitudes and heights”, the paper said.

Researchers said the impact of cloud cover on climate change cannot be ignored due to the significant contribution of this climate-forming parameter.

Cloud formation should be studied more carefully to improve climate forecasts, they said.

How and why clouds form has been a key area of interest for climate scientists, including the theory that cloud formation may be influenced by cosmic rays and the strength of magnetic energy from the Sun.