Photo: livescience
The Northern Hemisphere is now absorbing more solar energy than the Southern Hemisphere, and clouds are no longer able to maintain the previous balance.
For years, scientists observed a curious symmetry: both hemispheres reflected nearly equal amounts of sunlight back into space. This was attributed to the fact that the Northern Hemisphere has more land, cities, industrial aerosols, and pollution, which increase reflectivity, while the Southern Hemisphere is mostly ocean, absorbing more solar energy.
However, a new study published in PNAS shows that this symmetry is breaking down. Researchers analyzed NASA CERES satellite data, which has monitored Earth’s climate and energy balance since 2000. They found that the Northern Hemisphere is darkening faster than the Southern, absorbing more sunlight — a change that could affect weather patterns, precipitation, and the global climate in the coming decades.
CERES satellites measure how much sunlight is absorbed, reflected, and emitted as infrared radiation. Data from 2001 to 2024 indicate that the Northern Hemisphere absorbs roughly 0.34 watts more solar energy per square meter per decade than the Southern. While seemingly small, this difference is significant on a planetary scale.
Scientists identified the main contributors to the imbalance: melting snow and ice, reduced air pollution, and increased water vapor in the Northern Hemisphere. Melting exposes land and ocean surfaces that absorb more heat, cleaner air in China, the US, and Europe reduces reflective aerosols, and higher water vapor levels further trap heat.
Over the past two decades, cloud cover has remained largely unchanged. As a result, clouds no longer compensate for the hemispheric differences in sunlight reflection, and the precise reason for this phenomenon remains unclear.
