WASHINGTON (DAILY SUN CHRONICLE) โ A new NASA-supported study has found that the northern hemisphere is becoming dimmer than the southern hemisphere, a shift that could have significant implications for global climate patterns.
Using data from NASAโs Clouds and the Earthโs Radiant Energy System (CERES) satellite, researchers led by Norman Loeb of NASAโs Langley Research Center in Virginia discovered that the northern hemisphere is experiencing a net loss of radiative energy. The findings, published in the journal Proceedings of the National Academy of Sciences, indicate that the region is absorbing more sunlight and reflecting less, resulting in a darker appearance when viewed from space.
This imbalance affects Earthโs radiation budgetโthe balance between incoming solar energy and outgoing longwave radiation. Historically, ocean currents have helped redistribute energy between hemispheres, but the study found that these currents have not compensated for the disparity over the past two decades.
โThe emerging darkening of the NH relative to the SH is associated with changes in hemispheric differences in aerosolโradiation interactions, surface albedo, and water vapor changes,โ the authors wrote. โHow clouds respond to this hemispheric imbalance has important implications for future climate.โ
One major factor contributing to the dimming is the decline in Arctic sea ice. As reflective ice and snow are replaced by darker land and ocean surfaces, solar absorption increases, accelerating warming in polar regions. Scientists say this is a key reason why the Arctic is warming roughly four times faster than the global average.
Cloud cover has also decreased, particularly low-lying clouds that typically reflect sunlight. Researchers suggest that reduced pollution in the northern hemisphere may be partly responsible. Aerosolsโtiny particles from industrial emissionsโcan promote cloud formation, and fewer aerosols mean fewer clouds.
In 2024, the National Oceanic and Atmospheric Administration (NOAA) reported that reduced emissions from transoceanic shipping have led to a decline in โship tracks,โ or reflective cloud trails left by vessels. While cleaner air benefits public health, scientists caution that it may also reduce cloud reflectivity, inadvertently contributing to warming.
Meanwhile, the southern hemisphere has seen increased aerosol activity from natural events such as Australian wildfires and the Hunga Tonga volcanic eruptions in 2021 and 2022. These events have temporarily boosted reflectivity in the region.
The study estimates that the radiation budget gap between hemispheres is widening by approximately 0.34 watts per square meter per decade. Researchers warn that this divergence could skew climate models and complicate efforts to predict future climate scenarios.
Scientists are exploring geoengineering techniques, including stratospheric aerosol injection and marine cloud brightening, as potential ways to address the imbalance. However, these approaches remain controversial and require further study.
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