Record heat in 2023 has been linked to a decline in low-level clouds.

In 2023, global temperatures soared to an unprecedented 1.45°C above pre-industrial levels, exceeding predictions by 0.2°C. 

Research from the Alfred Wegener Institute attributes this anomaly to a sharp drop in low-altitude cloud cover, which has reduced Earth's ability to reflect solar radiation.  

Planetary albedo, Earth's measure of solar reflectivity, hit a record low in 2023. 

“2023 stood out as the year with the lowest planetary albedo since at least 1940,” says Dr Thomas Rackow of the European Centre for Medium-Range Weather Forecasts (ECMWF).

The reduction in low-altitude clouds, particularly in the northern mid-latitudes and tropics, has been identified as a primary cause, with the North Atlantic region showing significant changes.  

Low clouds provide a cooling effect by reflecting sunlight. Their reduction means the Earth absorbs more heat, exacerbating global warming.  

Existing climate models account for major warming drivers, including El Niño and greenhouse gas emissions, but still fall 0.2°C short. 

Dr Helge Goessling, lead author of the study, calls this discrepancy “one of the most intensely discussed questions in climate research”.  

Using energy budget models, researchers found that without the albedo reductions observed since 2020, 2023’s global temperature would have been 0.23°C lower. 

The North Atlantic, where sea-surface temperature records were broken, saw significant declines in low-altitude clouds over the past decade.  

The study suggests multiple factors behind reduced cloud cover, including lower levels of aerosols due to stricter marine fuel regulations. Aerosols contribute to cloud formation and reflect sunlight. 

Natural variability and ocean feedbacks may also play a role, though Dr Goessling says there is a possibility of a feedback loop where warming itself reduces low cloud cover.  

“If a large part of the decline in albedo is indeed due to feedbacks between global warming and low clouds, we should expect rather intense warming in the future,” Goessling said. 

This could accelerate the timeline for surpassing the 1.5°C threshold set by the Paris Agreement.  

The experts say their findings suggest a need for further investigation of the link between global warming and cloud dynamics. 

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