Balancing act: why Earth’s hemispheres reflect sunlight equally despite pollution, cloud, and climate differences

Earth’s Northern and Southern Hemispheres reflect the same amount of sunlight. Credit: NOAA

Scientists have long observed a puzzling fact about Earth: the Northern and Southern Hemispheres reflect nearly identical amounts of sunlight, despite vastly different environments and pollution levels. A new Geophysical Research Letters study used two decades of satellite data to investigate why, examining various components that reflect sunlight, including aerosols, land surfaces, and clouds. The scientists revealed that the Northern Hemisphere’s aerosols and land reflect more sunlight, balanced by the Southern Hemisphere’s low- and mid-level clouds. Observations from the past few decades show that both hemispheres are darkening over time, but it remains uncertain if this change is happening equally. This work enhances our understanding of Earth’s radiation budget and could help predict climate shifts, as further cloud adjustments may either stabilize or disrupt this symmetrical reflection.