Observational quantification of a total aerosol indirect effect in the Arctic

We use 6 yr of multisensor radiometric data (1998–2003) from the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program to provide an observational quantification of the short-wave aerosol first indirect effect in the Arctic. Combined with the previously determined long-wave indirect effect, the total (short-wave and long-wave) first indirect effect in the high Arctic is found to yield a transition from surface warming of +3 W m⁻² during March to a cooling of –11 W m⁻² duringMay, therefore altering the seasonal cycle of energy input to the Arctic Earth–atmosphere system. These data also reveal evidence of a first indirect effect that affects optically thinner clouds during summer, which may represent an additional negative climate feedback that responds to a warming Arctic Ocean with retreating sea ice.