JACKSONVILLE, Fla. – The sun’s warming rays met less resistance in 2023, as Earth experienced a record low in cloud cover.
Planetary albedo is how much sunlight is reflected into space by Earth’s surface and atmosphere. When Earth’s albedo is low, more sunlight is absorbed, causing more warming.
The main reason for this record-low cloud reflectivity was a significant decrease in low-altitude cloud cover, particularly over the Atlantic Ocean. These clouds usually reflect a lot of sunlight, helping cool the planet, but their decline has contributed to higher temperatures.
Scientists from the Alfred Wegener Institute (AWI) and the European Centre for Medium-Range Weather Forecasts (ECMWF) studied this unusual drop in albedo and found it could explain an extra 0.2 degrees Celsius of warming in 2023, which couldn’t be explained by other factors like greenhouse gases or the El Niño weather pattern. The team discovered that the decline in low clouds has been happening for the past decade, and it became especially noticeable in 2023.
Low-altitude clouds are critical for reflecting sunlight and cooling Earth. When these clouds decrease, more sunlight is absorbed, leading to higher temperatures. In contrast, higher-altitude clouds trap heat in the atmosphere, which warms the planet, similar to the effect of greenhouse gases. However, the decline in low clouds is what’s most concerning because it removes the cooling effect, causing more warming.
The researchers believe this decline in low clouds might be partly due to the reduction of aerosols in the atmosphere. Aerosols, which come from pollution and other sources, help clouds form and reflect sunlight.
Paradoxically, stricter regulations on pollution from ships have reduced aerosols, which may have contributed to fewer low clouds.
Another possible reason for fewer low clouds is global warming itself. As the planet heats up, it could be changing atmospheric conditions, making it harder for low clouds to form. If this trend continues, it could lead to even faster warming in the future, potentially pushing global temperatures past the 1.5 degrees Celsius limit set by the Paris Agreement sooner than expected.