LAUSR

The extent to which aerosols affect climate is highly uncertain. Observations of clouds interacting with aerosols from a volcanic eruption suggest that the effect is much smaller than was once feared. See Article p.485 Aerosols cast a wide shadow across many aspects of the Earth system. They reflect solar radiation, increase snow and ice melt, and contribute to local air pollution. Aerosols also interact with clouds, but the net effect of these interactions is difficult to disentangle from coinciding meteorological variations. Sulfate aerosols tend to increase reflection, and theoretical principles state that aerosols should lead to more but smaller cloud particles and should increase cloud lifetime and liquid water path. However, firm confirmation of these indirect effects has been hard to come by. Now, Florent Malavelle et al. use observations and modelling to help to understand the effects of a recent volcanic eruption in Iceland. The sulfate aerosols associated with the eruption caused a discernible yet transient brightening effect, but the effects on liquid water path were negligible. This result will help to reduce uncertainties in future climate projections, because results from climate models with excessive liquid-water-path responses can now be rejected.