Cleaner Clouds Offset Warming Current Models Miss
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- Researchers analyzed satellite observations of high clouds in the northern hemisphere from 2008 to 2018 and found clouds have become less icy as atmospheric dust levels dropped.
- The study, published in Geophysical Research Letters, attributes the dust decline to weakening surface winds driven by climate change, which have kicked up less dust over the past two decades.
- Dust particles seed ice crystals, so less dust means fewer ice crystals and more liquid droplets — and liquid droplets reflect more sunlight than ice crystals do.
- The added reflectivity from less icy clouds offsets about a quarter of the heating caused by other changes, such as an increase in high clouds that trap more heat.
- Current climate models do not yet incorporate this previously unidentified effect, meaning they may slightly overestimate the projected rate of global heating.
- The effect does not appear in southern hemisphere clouds because there is far less atmospheric dust there to begin with.
Why it matters: Climate models may need recalibration: they currently miss how falling dust — driven by weakening winds — makes northern hemisphere clouds more reflective, offsetting roughly a quarter of warming from other atmospheric changes. This doesn't reverse the warming trajectory but means projections could be modestly overestimating the rate of heating.
