Scientists say 4 billion people, about half the world’s population, experienced at least one extra month of extreme heat because of human-caused climate change from May 2024 to May 2025. The extreme heat caused illness, death, crop losses, and strained energy and health care systems, according to the analysis from World Weather Attribution, Climate Central and the Red Cross. The scientists say that without major cuts to greenhouse gas emissions, global temperatures will continue to rise, heat waves will become more frequent and severe, and adaptation measures will become less effective at protecting people.