The world's climate is warming up and, while debate continues about how much change we can expect, it is becoming clear that even small changes in climate can have major effects on the spread of disease. Erwin K Jackson, a member of Greenpeace International's Climate Impacts Unit and a delegate to the 11th session of the United Nations Intergovernmental Panel on Climate Change (Rome, 11‐15 December), reviews the scientific evidence of this new global threat to health.