Climate change is making heatwaves not only hotter, but effectively longer-lasting and larger in size, thus impacting more people, a new study finds. The research, published Friday in Science Advances, revealed heat domes — concentrations of high pressure air that drive up surface temperatures — move across the Earth’s surface 20% slower than they did in 1979, subjecting the people (and everything else) under them to their heat for longer.

The study also found the area covered by heat domes is larger, the temperatures are hotter, and global heatwaves are happening 67% more often than in 1979. Extreme heat is one of the clearest signals of climate change, mainly caused by the extraction and combustion of fossil fuels, and its deadliest impact.

“Those heat waves are traveling slower and slower so that basically means that … there’s a heat wave sitting there and those heat waves could stay longer in the region,” Wei Zhang of Utah State University, one of the study’s authors, said. “And the adverse impacts on our human society would be huge and increasing over the years.” (AP, New York Times $, AFP; Climate Signals background: Extreme heat and heatwaves)