People in the United States could see tens of thousands of extra violent crimes every year -- because of climate change alone.

"Depending on how quickly temperatures rise, we could see two to three million more violent crimes between now and the end of the century than there would be in a non-warming world," said Ryan Harp, researcher at the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder and lead author of a new study published today in Environmental Research Letters.

In 2018, Harp and his coauthor, Kris Karnauskas, CIRES Fellow and associate professor in the Department of Atmospheric and Oceanic Sciences at CU Boulder, mined an FBI crime database and NOAA climate data to identify a set of compelling regional connections between warming and crime rates, especially in winter. Warmer winters appeared to be setting the stage for more violent crimes like assault and robbery, likely because less nasty weather created more opportunities for interactions between people.

Now, the team has projected additional future violent crimes in the United States, by combining the mathematical relationships they uncovered in previous work with output from 42 state-of-the-art global climate models. The team accounted for key factors that previous studies have overlooked, including variations in crime rates across seasons and for different regions of the country.

"We are just beginning to scratch the surface on the myriad ways climate change is impacting people, especially through social systems and health," Karnauskas said. "We could see a future where results like this impact planning and resource allocation among health, law enforcement and criminal justice communities."