Bleached coral in the south Pacific in May. Rising temperatures contribute to the bleaching. Alexis Rosenfeld/Getty Images
Last year was the warmest year on record for the world’s oceans, part of a long-term warming trend. 2019 is by far the hottest, 2018 is second, 2017 is third, 2015 is fourth, and then 2016 is fifth.
Since the middle of last century, the oceans have absorbed roughly 93 percent of the excess heat caused by greenhouse gases from human activities such as burning coal for electricity. That has shielded the land from some of the worst effects of rising emissions.
Increasing ocean temperatures have harmed marine life and contributed to mass coral reef bleaching, the loss of critical ecosystems, and threatened livelihoods like fishing as species have moved in search of cooler waters. But the impacts of warming oceans don’t remain at sea.