Recent global temperature surge amplified by record-low planetary albedo

Recent global temperature surge amplified by record-low planetary albedo
by Robert Schreiber
Berlin, Germany (SPX) Dec 06, 2024

Rising sea levels, melting glaciers, and record-breaking marine heatwaves defined 2023 as a year of extraordinary climate shifts. The global average temperature soared to nearly 1.5 degrees Celsius above preindustrial levels, setting an all-time high. Scientists have struggled to account for this unexpected rise, as conventional factors like greenhouse gases, El Nino, and volcanic activity explain most - but not all - of the warming.

Researchers at the Alfred Wegener Institute (AWI) propose a critical contributing factor: a significant decline in planetary albedo, or the Earth's reflectivity. "In addition to El Nino and long-term warming driven by greenhouse gases, several other factors have been explored to explain the recent surge in global mean temperatures," said Dr. Helge Goessling, lead author of the study from AWI. "These include increased solar activity, elevated water vapor from volcanic eruptions, and reduced atmospheric aerosol particles. However, when combined, these factors still leave a 0.2-degree-Celsius gap unaccounted for."

This "explanation gap" has become a focal point for climate researchers, prompting AWI and the European Centre for Medium-Range Weather Forecasts (ECMWF) to delve into decades of satellite and reanalysis data. The findings point to 2023 as the year with the lowest recorded planetary albedo since at least 1940. "Planetary albedo, which measures how much solar radiation is reflected back into space, has shown a downward trend in recent years, with a significant drop in 2023," said co-author Dr. Thomas Rackow of ECMWF.

Declining low-altitude clouds

The study attributes much of the albedo decline to a reduction in low-altitude clouds, particularly in the northern mid-latitudes and tropics. This trend is most pronounced over the eastern North Atlantic, a region that also recorded extraordinary temperature anomalies in 2023.

Lower clouds play a vital role in reflecting sunlight, providing a cooling effect. Unlike higher-altitude clouds, which can trap heat and contribute to warming, fewer low clouds result solely in reduced cooling. "If there are fewer low clouds, we only lose the cooling effect, making things warmer," explained Goessling.

Causes of reduced cloud cover

Stricter regulations on marine fuel, which reduce the concentration of aerosols - critical for cloud formation - likely contributed to the decline in low clouds. Additionally, natural fluctuations and ocean feedbacks have played a role. However, Goessling cautions that these factors alone may not fully explain the trend. "Global warming itself could be reducing the number of low clouds through feedback mechanisms, as indicated by some climate models," he added.

Implications for future warming

The decline in albedo has serious implications for global climate targets. If low cloud cover continues to decrease, feedback loops between warming and albedo loss could lead to accelerated temperature increases. "We could see long-term global warming surpassing 1.5 degrees Celsius sooner than expected," Goessling warned. This would necessitate a reevaluation of remaining carbon budgets under the Paris Agreement and urgent adaptation measures for intensifying weather extremes.

Research Report:Recent global temperature surge intensified by record-low planetary albedo