Item

Abstract

A hearing was organized by the European Commission (DG Environment and DG Joint Research Centre) on behalf of the European Union Climate Change Expert Group on Science, with the aim to update non-expert policy-makers on the role of aerosols in the climate system. The focus was on new knowledge that came available since the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC TAR, 2001). The present report does not pretend to provide information with the status of the IPCC. The experts anyway agreed that the following statements are robust, hence that they are not likely to change as scientific uncertainties are further reduced: • the increase of the atmospheric aerosol concentration since pre-industrial times (1750) has resulted globally in a cooling, which magnitude is significant when compared with the warming due to greenhouse gases (GHG). • the probability that the climate sensitivity is in the upper part of the range proposed by the IPCC TAR, i.e. larger than 2.5 °C for a doubling of the atmospheric CO2 concentration, is therefore higher. • reductions of black carbon and organic matter emissions from fossil fuel combustion (diesel in particular) would be beneficial for human health and would very likely counter-act partially the warming expected from ongoing reductions in sulfate and nitrate aerosols. • in order to stabilize CO2 equivalent concentrations there is an urgent need to reduce CO2 emissions, however the potential of reducing non-CO2 greenhouse gases, in particular CH4 and tropospheric ozone, should be explored as well.