If global temperatures increase by 1 degree Celsius (C) or more than current levels, each year billions of people will be exposed to heat and humidity so extreme they will be unable to naturally cool themselves, according to interdisciplinary research from the Penn State College of Health and Human Development, Purdue University College of Sciences and Purdue Institute for a Sustainable Future. Results from a new article published today (Oct. 9) in Proceedings of the National Academy of Sciences indicated that warming of the planet beyond 1.5 C above preindustrial levels will be increasingly devastating for human health across the planet.