Climate Change Is Cooking the Oceans

A new paper in Nature shows how marine heat waves have become more common and intense in recent decades, largely due to climate change.

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The role of human-caused climate change in intensifying land-based heat waves is now well-established. But less research has focused on the ocean, where extreme heat events in recent years have wiped out portions of the Great Barrier Reef, caused bull sharks to migrate further north, and left scientists scrambling to find ways to save coral. Individual events like the 2016 heat wave in the Great Barrier Reef have been tied to climate change (it made the heat wave 175 times more likely), but there hasn’t been a big picture look at the topic featuring projections into the future.

That’s what led a team of Swiss researchers used a mix of models and satellite measurements to get a handle on how marine heat waves have already changed and what the future holds for the globe. The satellite record, which runs from 1982-2016, helped ground truth the models they used to create a pre-industrial baseline—what the oceans looked like without all the extra heat trapped by greenhouse gas emissions. They then used the models to understand how climate change is affecting the extent, duration, and intensity of marine heat waves as well as project future changes.

The findings show the number of marine heat wave days doubled between 1982 and 2016, while heat waves also increased in extent and intensity. Moreover, they show that 87 percent of marine heat waves can be attributed to climate change, meaning they would not have occurred without it.