Ocean heat waves are becoming more common and lasting longer

The extreme events can kill corals and kelp and throw marine ecosystems into chaos

kelp forest

SWELTERING STRANDS  In 2011, a marine heat wave off Australia’s southern coast devastated the towering kelp forests of the Great Southern Reef (shown).

Emma Flukes

The world’s oceans are sweltering. Over the last century, marine heat waves have become more common and are lasting longer. New research suggests the annual number of days that some part of the ocean is experiencing a heat wave has increased 54 percent from 1925 to 2016, researchers report April 10 in Nature Communications.

Typically, scientists define a marine heat wave as at least five consecutive days of unusually high temperatures for a particular ocean region or season. These extreme temperatures can be lethal for marine species such as corals, kelp and oysters, and can wreak havoc on fisheries and aquaculture (SN: 2/3/18, p. 16).

In the new study, the researchers searched for such events recorded in sea surface temperature data recorded as far back as 1900 and in satellite data since 1982. Not only have the heat waves become 34 percent more common on average, but they also last an average 17 percent longer, the team found.

That trend is mostly influenced by climate change causing surface ocean waters to warm, rather than by large atmosphere-ocean climate patterns, such as the periodic warming and cooling of waters in the equatorial Pacific called the El Niño-Southern Oscillation. The researchers predict even more frequent marine heat waves in coming decades.   

Carolyn Gramling is the earth & climate writer. She has bachelor’s degrees in geology and European history and a Ph.D. in marine geochemistry from MIT and the Woods Hole Oceanographic Institution.

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