The first study of its kind shows that ecosystems experience far more cumulative heat than standard measurements reveal. Prolonged, cumulative heat exposure, especially when combined with other stressors, can create conditions that some species may not be able to survive.” “Many laboratory experiments simulate marine heatwaves by increasing temperatures for a few days or weeks in total. Our research provides a new framework for designing experiments that reflect natural marine heatwave conditions and quantify cumulative heat exposure, allowing scientists to better evaluate the biological impacts of marine heatwaves across ecosystems.” That work also identified links between marine heatwaves and large-scale climate patterns, including El Niño and the Pacific Decadal Oscillation.