The impact of climate change on the spread of disease and the affect on world health could be dramatic. In poorer countries the chances of catching a life-threatening disease could certainly increase. In Jakarta, according to the city’s health experts, climate change means the rainy season is lasting longer. And that means disease-carrying mosquitoes continue to thrive in places where previously they could not survive. The disease in this case is dengue – for which there is no cure. Worldwide an estimated 100 million people are infected with dengue every year. Experts are concerned health systems around the world, which are already under considerable strain, will be subjected to an almost intolerable pressure as climate change takes hold. And it’s not just in poor countries. Rich countries are vulnerable as well. A deadly heat wave hit Chicago in 1995 killing hundreds of people. In 2003 a heat wave swept through Europe killing 70,000 people. In Paris at least a thousand died. “Hot Cities” visits all three cities, Jakarta, Paris and Chicago, to see what lessons have been learnt and how they are coping.