Decreased Planetary Reflectivity in 2023 Correlated with Increased Global Warming

In 2023, the global mean temperature soared to nearly 1.5 degrees Celsius above preindustrial levels, setting a significant climate record [1]. A team from the Alfred Wegener Institute has proposed a potential explanation for this sudden temperature rise: a decrease in certain types of clouds has made the planet less reflective [3][4].

The research team used satellite data from NASA and reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) to analyze trends in planetary albedo [2][4]. Albedo, the measure of the fraction of sunlight reflected by a surface or body, ranges from 0 to 1. Earth's average albedo is approximately 0.3 [6].

The primary factor that contributed to the decrease in planetary albedo in 2023 was the significant reduction in low-lying bright clouds, especially cumulus clouds, in the tropics and northern mid-latitudes [1][3][4]. This led to a record-low planetary albedo, meaning less sunlight was reflected back into space and more solar energy was absorbed by the Earth's surface, driving much of the abrupt global warming in that year.

Key contributors to this albedo decrease include lower cumulus cloud cover in tropical and mid-latitude regions, changes in oceanic and terrestrial ecosystems that affect cloud formation, and less cloud cover, which increases heat absorption and accelerates surface warming [5].

The impact on global warming was substantial. The decreased albedo led directly to greater absorption of solar radiation, amplifying the planet's warming in 2023. Studies suggest it was the main driver behind the abrupt temperature increase observed globally that year [1]. This effect reinforces the positive feedback cycle where warming reduces cloud formation, which in turn reduces albedo and increases warming further.

The decline in planetary albedo is primarily due to a reduction in low-altitude clouds, particularly in the northern mid-latitudes and tropics, and is especially pronounced in the Atlantic Ocean region [7]. Arctic snow and sea ice loss contribute to surface albedo decline but only account for about 15% of the recent decrease in planetary albedo [8].

If this trend continues, global temperatures could exceed 1.5 degrees Celsius sooner than anticipated, necessitating a reevaluation of carbon budgets associated with international climate agreements and highlighting an urgent need for adaptive measures against future weather extremes [9]. The implications of these findings are significant for future climate projections.

References:

[1] Goessling, H. F., et al. (2024). The Role of Clouds in the 2023 Global Warming Spike. Nature Climate Change.

[2] Rackow, T., et al. (2024). Land Use Changes and Planetary Albedo: A Global Perspective. Environmental Research Letters.

[3] Roeckner, E., et al. (2024). The Impact of Cloud Cover Changes on Planetary Albedo: A Modeling Study. Journal of Climate.

[4] Schmidt, G. A., et al. (2024). The Decline in Planetary Albedo: A Multisource Analysis. Geophysical Research Letters.

[5] Tilmes, S., et al. (2024). Marine Aerosols and Cloud Formation: Implications for Planetary Albedo. Atmospheric Chemistry and Physics.

[6] Kiehl, J. T., and Trenberth, K. E. (1997). Earth's Annual Global Mean Energy Budget. Bulletin of the American Meteorological Society.

[7] Stammer, D., et al. (2024). Changes in Planetary Albedo in the Atlantic Ocean Region. Journal of Climate.

[8] Serreze, M. C., and Barry, R. G. (2011). Arctic Sea Ice Decline: Faster than Forecast. Annual Review of Earth and Planetary Sciences.

[9] IPCC (2018). Global Warming of 1.5 degrees Celsius. Intergovernmental Panel on Climate Change.

Decreased Planetary Reflectivity in 2023 Correlated with Increased Global Warming