Earth's brightness is falling, driving higher solar energy absorption, studies find

Earth's capacity to reflect solar radiation has dropped measurably over the past two decades, with scientists linking the trend to reduced cloud cover and rising temperatures, according to recently published research. A 2021 study in Geophysical Research Letters used Earthshine data — light reflected from the planet onto the dark side of the Moon — alongside measurements from NASA's CERES satellites, covering 1998 to 2017. It found a decline in planetary reflectance equivalent to roughly 0.5 watts per square meter of retained solar energy. A separate paper published in Science showed global reflectance reached a record low in 2023, largely tied to a drop in low-altitude clouds over the mid-northern latitudes and the tropics. Researchers estimated the change could account for about 0.2 degrees Celsius of the unexpected temperature rise recorded that year. A newer study published in 2026 covering mid-2003 to mid-2024 attributed half of the imbalance in Earth's energy budget during that period to reductions in low cloud cover. A Nature Communications analysis the same year tied declining anthropogenic aerosols to smaller cloud droplets and greater energy retention over oceans. The studies point to melting sea ice and snow exposing darker surfaces, alongside shifts in cloud composition driven by warming, greenhouse gases and changing aerosols, as drivers of the trend. The researchers said Earth's energy imbalance has more than doubled in recent decades, calling it among the clearest physical indicators that climate change continues to accelerate.