A new study has found that cleaner clouds are helping to slow the rate of global heating. Falling levels of dust in the atmosphere are making clouds more reflective, a previously unidentified effect that is not accounted for in current climate models. This may mean that projections of global heating are slightly overestimated.
Study details and findings
Researchers analyzed satellite observations of high clouds in the northern hemisphere from 2008 to 2018, assessing the ratio of ice crystals to liquid droplets. The findings, published in Geophysical Research Letters, show that clouds have become less icy over that period. Weakening surface winds due to climate change have resulted in less dust being whipped up into the atmosphere over the last two decades. Dust particles help seed ice crystals, so less dust means fewer ice crystals in clouds.
Regional differences and impact
The effect is not observed in southern hemisphere clouds because there is far less dust in the southern hemisphere atmosphere to begin with. Liquid droplets reflect more sunlight than ice crystals do. The study suggests that the extra 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.
Implications for climate projections
According to the researchers, this is no reason for complacency, but it potentially means global warming will not happen as fast as current models predict. The findings highlight the need to incorporate this effect into climate models for more accurate projections.
