Unlucky Weather Could Have Made the 2023 North Atlantic Marine Heatwave Far

A new modeling study suggests the 2023 North Atlantic marine heatwave, while extreme, could have been far worse under slightly different weather patterns. The research, published in Nature Communications by Catherine H. Gregory, Urs Hofmann Elizondo, Thibault Guinaldo and Thomas L. Frölicher, used an approach called ensemble boosting to generate physically plausible alternative evolutions from the same large-scale climate setup. In the boosted simulations, marine heatwaves lasted up to 579 days, hit peak intensities of 4.5°C above long-term averages, and accumulated 717 degree-days of heat stress. By comparison, the observed event ran about 240 days, peaked near 2.9°C above normal, and totaled 224 degree-days. The study frames much of the gap as “luck” in day-to-day variability.