The threat to human health from climate change is so great that it could undermine the last fifty years of gains in development and global health, according to a major new Commission, published in The Lancet. However, the report provides comprehensive new evidence showing that because responses to mitigate and adapt to climate change have direct and indirect health benefits – from reducing air pollution to improving diet – concerted global efforts to tackle climate change actually represent one of the greatest opportunities to improve global health this century.