Equilibrium & Sustainability

Climate-driven extreme heat is ‘new normal’ for oceans: study

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More than half of the planet’s ocean surface has surpassed historical extreme heat thresholds on a regular basis since 2014, a new study has found.

The study, published in PLOS Climate, concluded that such excessive ocean temperatures, fueled by climate change, have now become the “new normal.” These heat extremes are threatening crucial marine ecosystems, including coral reefs, seagrass meadows and kelp forests — by altering their structure and function, while jeopardizing their ability to provide sustenance to human communities, according to the authors.

“Climate change is not a future event,” Kyle Van Houtan, who headed the research team during his tenure as chief scientist for Monterey Bay Aquarium, said in a statement.

“The reality is that it’s been affecting us for a while,” he added. “Our research shows that for the last seven years more than half of the ocean has experienced extreme heat.”

Researchers at the California aquarium mapped out 150 years of sea surface temperatures in order to identify a fixed historical benchmark for marine heat extremes — as well as how often and how much of the ocean exceeded this point, a news release accompanying the study said.

While 2014 was the first year in which more than half of ocean surpassed that threshold, this upward trend continued in the years that followed, and reached 57 percent of the ocean by 2019, according to the study.

As a basis of comparison, just 2 percent of the ocean surface was experiencing such warm temperatures at the end of the 19th century, the authors found.

The temperature shifts identified by the researchers grew out of an initial exploration of the history of kelp forest changes throughout California, according to the news release. As part of that study, Van Houtan and his colleagues began quantifying and mapping out sea surface heat extremes — key stressors for kelp — along California’s coast over the past century.

The authors said they later decided to expand their investigation beyond California, with a goal of understanding the frequency and location of extreme marine heat around the world.

To do so, they used historical records to determine average temperatures for the ocean’s surface from 1870 to 1919 — identifying the top 2 percent of temperature increases during that period as “extreme heat,” according to the study.  Then they mapped extremes for the next century that followed, to determine whether such events were becoming more frequent.

“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 in a statement.

Given the increasing evidence that extreme heat has become a new normal across most of the ocean’s surface, the authors emphasized the need to curb emissions from generated by fossil fuels, which they described as “the driver of climate change.”

As the ocean heats up and as its ecosystems collapse, so too does their ability to buffer low-lying coastal regions from severe weather or to serve as a carbon sink for human-generated greenhouse gas emissions, according to Van Houtan.

“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,” he said in a statement. “We are experiencing it now, and it is speeding up.”

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