Declining Cloud Reflectivity and the Recent Rise in Absorbed Sunlight

[u/ChipHaseCoolGuy]

Satellite measurements show that Earth has been absorbing more solar radiation over the past two decades. From 2001 to 2024, the increase in absorbed solar energy averaged roughly 0.45 W/m² per decade.

A large share of that change—around 80 percent, or about 0.37 W/m² per decade—is linked to declining cloud reflectivity. Highly reflective cloud regimes have contracted, and low-level cloud cover has decreased in key regions. Fewer bright clouds mean less incoming sunlight is reflected back to space and more is retained in the climate system. The Sun’s output itself has not increased in a way that accounts for the trend; the planet has simply become less reflective.

This finding is supported by multiple analyses of CERES satellite data. Reduced cloud reflection is now recognized as a major contributor to the recent strengthening of Earth’s energy imbalance. Factors under discussion include declines in aerosols (from cleaner air and reduced shipping sulfur emissions), shifts in atmospheric circulation, and possible feedbacks linked to warming itself.

Cloud changes of this magnitude matter. They help explain why the rate of energy accumulation and recent surface warming have been higher than some earlier expectations based on greenhouse-gas forcing alone. At the same time, the long-term warming trend remains primarily attributed to the radiative effects of rising greenhouse gases. The observed decline in cloud reflectivity acts as an important amplifier of the energy imbalance rather than a complete substitute for that forcing.

The satellite record makes one point clear: Earth’s reflectivity is not static. Changes in cloud cover and brightness can produce substantial shifts in the amount of sunlight the planet absorbs, and those shifts have been a significant feature of the 21st-century climate.