Nobel Laureate Paul J. Crutzen (Chemistry 1995), who recently stepped down as the director of the Max Planck Institute for Chemistry, gave a special seminar at the ICTP on 25 October. Sponsored by the ICTP Physics of Weather and Climate Group, Crutzen's presentation examined how pollution in the tropics, caused by biomass burning and other factors, is affecting the chemistry of the atmosphere. That, in turn, may be influencing regional climates in many tropical areas. He contends that such environmental impacts must be factored into global climate research to enhance the accuracy of mathematical models. Crutzen, who plans to return to the Centre next year, also discussed potential avenues of co-operation for enhancing climate change research in developing countries.