A new study led by the Monterey Bay Aquarium has revealed that extreme heat has become the “new normal” for the ocean. Based on 150 years of data, the researchers found that the majority of the ocean’s surface has regularly exceeded a historical heat extreme threshold for the last seven years.
Heat extremes can destroy critically important marine ecosystems, including coral reefs, seagrass meadows, and kelp forests. Thermal stress alters the functioning of these ocean habitats, and gradually compromises their ability to adapt and survive.
“Climate change is not a future event,” said Dr. Kyle Van Houtan, who led the research team. “The reality is that it’s been affecting us for a while. Our research shows that for the last seven years more than half of the ocean has experienced extreme heat.”
“These dramatic changes we’ve recorded in the ocean are yet another piece of evidence that should be a wake-up call to act on climate change. We are experiencing it now, and it is speeding up.”
By mapping 150 years of sea surface temperatures, the experts established a historical benchmark for ocean heat extremes. The study revealed that 2014 was the first year that this threshold was exceeded throughout more than half of the ocean. By 2019, 57 percent of the ocean experienced excessive heat.
For comparison, only two percent of the ocean surface was experiencing extremely 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,” said Dr. Van Houtan.
According to the researchers, the new normal of extreme heat across the majority of the ocean’s surface is further evidence for the urgent need to drastically reduce emissions from the burning of fossil fuels, which are the driver of climate change.
“When marine ecosystems near the tropics experience intolerably high temperatures, key organisms such as corals, seagrass meadows, or kelp forests can collapse,” said Dr. Van Houtan.
“Altering ecosystem structure and function threatens their capacity to provide life-sustaining services to human communities like supporting healthy and sustainable fisheries, buffering low-lying coastal regions from extreme weather events, and serving as a carbon sink to store the excess carbon put in the atmosphere from human-generated greenhouse emissions.”
The study is published in the journal PLOS Climate.