By 2023, the number of low-altitude clouds will have decreased dramatically.
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Changes in cloud cover may be the reason global temperatures have exceeded climate model predictions over the past two years.
Temperature records were broken repeatedly in 2023 and 2024, with average temperatures in both years about 1.5 degrees Celsius above pre-industrial levels. Climate change and El Niño weather patterns are partly to blame, but neither factor can fully explain the unusually warm weather.
Researchers now think the answer lies in a sharp decline in low-lying cloud cover in 2023. This change reduced Earth’s albedo, the planet’s ability to reflect solar radiation back into space, causing temperatures to rise.
Earth’s albedo has been decreasing since the 1970s. This is mainly due to the melting of polar ice sheets, which help reflect sunlight back into space. However, an analysis of satellite data by Helge Goessling of the Alfred Wegener Institute in Germany and his colleagues revealed that the planet’s albedo in 2023 hit an all-time low.
Goessling and his colleagues then used a combination of weather observations and modeling to understand the cause of this decline, and found that the number of low-lying clouds decreased sharply in 2023. This change was particularly noticeable in the Atlantic Ocean. 2023 saw the most unusual temperature extremes.
“We were able to show where the clouds were actually changing and at what altitude in the atmosphere,” Gosling said. “It’s really surprising that this reduction in cloud cover is occurring primarily in the lower levels.”
The findings could explain an additional 0.2°C of heat loss that scientists have struggled to account for, once background climate change and the effects of El Niño in 2023 are added up. “This is another piece of the puzzle, but I think it’s a very important piece,” Goessling said. Although the study only evaluated data from 2023, the findings could also explain why global temperatures will remain extremely high through 2024, despite El Niño weakening earlier this year. be.
Professor Paulo Cheppi, from Imperial College London, said the study was timely as climate scientists were keen to understand the drivers of recent record warmth. “I think they make a pretty convincing case that changes in albedo, especially in low-level clouds, contribute significantly to changes in the radiation budget and, therefore, in temperature,” he says.
The next question is why low-altitude clouds disappear. There are three main explanations. This may be due to a global decrease in aerosol pollution, which promotes cloud formation and persistence. Alternatively, it could be the result of changes in cloud behavior due to global warming. Or it could just be natural fluctuations in climate.
Understanding which of these three factors is dominant is critical because it influences how sensitive Earth’s climate is to greenhouse gas pollution. If the lack of clouds is due to a climate change feedback, its effects will accelerate in coming years, causing global temperatures to rise more than expected. “The answer has pretty deep implications for what we expect about future climate change,” Seppi says.
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