Extreme Heat Is the Ocean's "New Normal"

A new analysis of a century-and-a-half of data shows excessively warm ocean temperatures are the new normal.

The analysis, led by Kyle Van Houtan, a 2006 doctoral graduate of Duke University’s Nicholas School of the Environment and former director of science at the Monterey Bay Aquarium, reveals that the majority of the ocean’s surface has experienced extreme heat regularly since 2014.

This is altering the structure and function of crucial marine ecosystems, including coral reefs, seagrass meadows and kelp forests, and increasing their risk of collapse, Van Houtan said. It’s also undercutting their capacity to continue providing life-sustaining services that humans depend on, such as supporting healthy fisheries, buffering low-lying coastal areas from extreme storms, and absorbing fossil-fuel-derived carbon from the atmosphere.

“Climate change is not a future event,” Van Houtan said. “The reality is that it’s been affecting us for a while. By focusing on heat extremes, we hope to provide an alternative framework that may help better contextualize the dramatic changes currently occurring in marine systems”

He and his co-lead author Kisei Tanaka, also of the Monterey Bay Aquarium, published their peer-reviewed study Feb. 1 in the open-access journal PLOS Climate.

To conduct the study, they collected and mapped 150 years of data on sea surface temperatures worldwide to determine a fixed historical benchmark for marine heat extremes. They then recorded how often and how much of the ocean exceeded the threshold.

By 2019, the last year for which data was analyzed, 57% of the ocean was regularly experiencing temperatures above the benchmark, compared to just 2% at the end of the 19th century.

“Today, the majority of the ocean’s surface has warmed to temperatures that only a century ago occurred as rare, once-in-50-year extreme warming events,” Van Houtan said.

Some regions began experiencing extreme heat regularly even earlier than 2014, the study shows. The South Atlantic began exceeding the benchmark in 1998, and the Indian Ocean began exceeding it in 2007.

Van Houtan is currently president and chief executive officer at the Loggerhead Marinelife Center in Juno Beach, Fla. He also holds an appointment as adjunct associate professor at Duke’s Nicholas School.

Reference: Tanaka KR, Houtan KSV. The recent normalization of historical marine heat extremes. PLOS Climate. 2022;1(2):e0000007. doi:10.1371/journal.pclm.0000007

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