Climate change poses such a threat to human health that it could undermine all the gains in global development during the past 50 years, an independent international commission reports on Tuesday. The review, led by experts on medicine and economics at University College London and published in the Lancet, says immediate action is needed to avert the direct health impacts of climate change through heatwaves, other extreme weather events and the spread of infectious diseases — and indirect effects through factors such as forced migration and crop failures.