If the world does not curb its greenhouse gas emissions, by the end of this century, the number of people dying annually because of extreme heat will be greater than the current global death toll from infectious diseases - that’s all infectiousness diseases, from malaria to diarrhoeal diseases to HIV. This is the grim assessment of climate researchers and economists of the Climate Impact Lab in the largest global study to date of health and financial impacts of temperature-related deaths. Roland Pease of BBC talks to Solomon Hsiang, co-director of the Climate Impact Lab.