## NASA Data Reveals Earth is Darkening, With Growing Imbalance Between Hemispheres
A new study analyzing 24 years of data from NASA satellites indicates that Earth is reflecting less sunlight back into space, a phenomenon known as decreasing albedo, and that this change is happening at a faster rate in the Northern Hemisphere (NH) compared to the Southern Hemisphere (SH). Published in *PNAS*,the research highlights a growing energy imbalance with potentially significant implications for climate change.
The Earth’s energy budget – the balance between incoming solar radiation and outgoing radiation – is a crucial factor in driving ocean and atmospheric circulation. Researchers found that while both hemispheres are experiencing a decrease in reflectivity, the Northern hemisphere is darkening more rapidly. This means the NH is absorbing more solar radiation while simultaneously emitting more outgoing longwave radiation.
Several factors contribute to this effect, including variations in cloud cover, snow cover, and the amount of water vapor present in the atmosphere. Previous research suggested that atmospheric and oceanic circulation could compensate for imbalances between the hemispheres. However,this new study indicates that the current changes are not being fully offset by these natural processes.
Specifically, the darkening in the Northern Hemisphere, driven by changes in aerosols, surface albedo, and water vapor, isn’t being counteracted by corresponding changes in cloud cover. This suggests a potential limit to the role clouds play in maintaining hemispheric symmetry in albedo. Climate models predict a continued increase in this asymmetry as CO2 levels rise and aerosol concentrations shift. While clouds *could* eventually compensate through circulation changes, this process may occur over a longer timescale.
The research also reveals that the Northern Hemisphere is warming at a faster rate than the Southern Hemisphere, and the Northern Hemisphere tropics are becoming wetter. These observations point to a shift in large-scale atmospheric circulation patterns globally.
While the findings are significant, the researchers emphasize the need for continued monitoring. The relatively short observational record currently available prevents definitive conclusions, and a longer dataset is required to precisely track the evolution of radiation, cloud patterns, and atmosphere-ocean circulation. The study suggests the Northern Hemisphere extratropics will likely continue to darken relative to the Southern Hemisphere, but further research is vital to confirm this trend.
