Nic Lewis reports on the publication of a very important paper in Journal of Climate. Bjorn Stevens has created a new estimate of the cooling effects of pollution ("aerosols") on the climate. Readers will no doubt recall that to the extent that aerosol cooling is small the warming effect of carbon dioxide must also be small so that the two cancel out to match the observed temperature record. Only if aerosol cooling is large can the effect of carbon dioxide be large. --Andrew Montford, Bishop Hill, 19 March 2015
