Professor Jan Semenza is an environmental epidemiologist with 30 years of experience in climate change and health. He led the US CDC response to the 1995 heat wave in Chicago that claimed the lives of more than 700 individuals. Most recently he was the head of the Health Determinants Section at the European Centre for Disease Prevention and Control (ECDC), where he spearheaded research on infectious diseases and climate change. He was a lead author of the IPCC AR6 report, co-author of the Lancet Countdown reports and is the co-lead of WG1 and WG2 of the Lancet Countdown in Europe.