Climate change is causing frequent, well-studied, extreme heat events. Less well understood is the additional heat stress experienced by billions of people as a result of those extreme heat events. However, a new study published in Nature Climate Change aims to change that. The study analyzed more than 70 years of climate data stored in the ERA5-HEAT data set, which includes heat stress data going back to 1940. The researchers combined that climate information with population data to estimate human exposure to hazardous heat worldwide. The study found that nighttime “feels-like” temperatures have increased faster than daytime temperatures. Around 70% of the world’s population now experiences at least 90 days of strong heat stress annually, compared with 55% in the 1970s. They found that hazardous heat stress has intensified across every continent over the last five decades, including in places historically unaccustomed to such heat like parts of Europe. A recent heat wave in Europe is said to have caused more than 10,000 excess deaths. “Heat stress is already affecting lives worldwide and is no longer a future threat,” Rebecca Emerton, lead author of the study, and a senior scientist with the European Centre for Medium-Range Weather Forecasts, told Mongabay in a video call. Extreme heat causes more human deaths than any other extreme weather event; children and the elderly are particularly vulnerable. Underlying health conditions including asthma, diabetes and cardiovascular disease can become deadly with heat. “This study provides strong evidence that heat stress is increasing globally and that…This article was originally published on Mongabay