Extreme weather is contributing to undocumented migration and return between Mexico and the United States, suggesting that more migrants could risk their lives crossing the border as climate change fuels droughts, storms and other hardships, according to a new study. People from agricultural areas in Mexico were more likely to cross the border illegally after droughts and were less likely to return to their original communities when extreme weather continued, according to research this week in the journal Proceedings of the National Academy of Sciences. The finding that return migration decisions were delayed by weather stress in origin communities is “important and novel,” said Benveniste, who studies climate-related human migration and was not involved in the study.