Disappearing clouds may be behind mysterious heat

The Earth was inexplicably warm last year – and the models have so far failed to explain why. But now German researchers may be a worrying solution to the tracks – some of the clouds have disappeared.

Last year was record warm on Earth – 1.5 degrees warmer than pre-industrial times. The weather phenomenon El Niño and human emissions of greenhouse gases are responsible for a large part of the temperature increase – but not all of it, according to the researchers’ models. 0.2 degrees of the increase was unexplained.

Helge Gössling, a climate physicist at the German Alfred Wegener Institute, decided together with some colleagues to look at the planet’s albedo – reflectivity.

Bouncing into space

When the sun’s rays reach the planet, some bounces back into space.

– If you think of the surface of the earth, there are some very reflective surfaces such as ice, snow and the desert, while the oceans, on the other hand, are quite dark, says Gössling.

The oceans absorb about 95 percent of the heat if the sun shines directly on them.

– But if you have clouds instead of a dark sea, you reach an albedo of 50%, if it is overcast.

When the researchers looked at the low-lying cloud cover for 2023 using satellite data, they discovered that it was unusually weak, about 4 percent less than a normal year, including over the tropics. It could be that the Earth’s reflectivity last year was the lowest since the 1940s, and enough to explain the 0.2 degree difference.

– The 0.2 degrees is a lot, because it is actually about the current warming. If the long-term temperature increase is somewhere around 1.3–1.4, then it is more than a tenth of that, says Gössling.

Disturbing theory

So where have the clouds gone? Gössling highlights natural variations or that shipping has reduced its emissions of sulfur dioxide, which may have led to reduced cloud formation. A third, more worrying theory is that climate change is causing the decline. If this is true, then a warmer climate leads to less clouds, which in turn leads to the earth warming up faster, which may mean that climate models need to be adjusted.

– I wouldn’t say that this changes how worried you should be about global warming in the future, says Gössling and continues:

– But you can say that the best possible outcome has become worse.

Cloud researcher Vaughan Phillips at Lund University says that the study is in line with previous research that has shown a connection between low clouds and climate change.

– It is very interesting to see these 0.2 degrees connected to it, and it is very reasonable, he says.

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