Earth is slowly dimming, and scientists say the reason lies in how sunlight interacts differently across the planet’s two halves. The finding, drawn from 24 years of NASA satellite data, reveals a worrying imbalance between the Northern and Southern Hemispheres.
Is Earth reflecting less sunlight into space?
Researchers examined data from NASA’s Clouds and the Earth’s Radiant Energy System, or CERES, which began operations in 1997. The project measures how much sunlight Earth absorbs and how much infrared radiation it releases into space. These figures form the planet’s energy budget, a key factor controlling weather and climate.
The new study, published in PNAS, shows that both hemispheres are becoming darker, but the Northern Hemisphere is losing light more rapidly. This means it is absorbing more sunlight than the Southern Hemisphere, a change that may accelerate warming.
What causes this imbalance between hemispheres?
According to the research team, several factors drive the difference, including changes in cloud patterns, snow cover, surface albedo and atmospheric water vapour. Earlier studies suggested that ocean and air circulation could balance such energy differences. However, the new data indicate that this natural correction might not be working as effectively as once believed.
The scientists also found that clouds may have a limited capacity to maintain balance in Earth’s albedo, or reflectivity. “There may be a limit to clouds’ role in maintaining hemispheric symmetry in albedo,” the researchers noted in their paper.
Could this affect the planet’s future climate?
The study suggests that the Northern Hemisphere could continue warming faster than the Southern Hemisphere. It also points to wetter conditions in northern tropical regions, signalling shifts in large-scale atmospheric circulation.
“The hemispheric difference in surface warming and albedo in response to rising CO₂ levels may increase in the future,” the researchers added. They warned that if clouds fail to offset these changes, the imbalance could persist or worsen.
What comes next for scientists?
The researchers emphasised the need for a longer observation record to track how radiation, clouds and ocean circulation evolve over time. For now, their findings suggest the Northern Hemisphere’s bright blue skies may be dimming more quickly than the rest of the planet—a subtle but serious sign of change in Earth’s delicate energy balance.
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