Extreme heat driven by climate change is new normal for oceans

More than half of the world’s ocean surface has surpassed historic extreme heat thresholds on a consistent basis since 2014, according to a new study by the Monterey Bay Aquarium and published in the journal PLOS Climate.

The heat extremes, driven by climate change, put critical marine ecosystems like coral reefs, seagrass meadows, and kelp forests at risk of collapse and threaten their ability to provide for local human communities, the researchers found.

“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,” said Kyle Van Houtan, leader of the research team during his tenure as chief scientist for the aquarium. “We are experiencing it now, and it is speeding up.”

Researchers conducted the study by mapping 150 years of sea surface temperatures to find a fixed historical benchmark for marine heat extremes. They then analyzed how much and how often the ocean surpassed that heat benchmark.

Researchers discovered that more than half of the ocean saw heat extremes in 2014. The extreme heat trend continued over the next several years and reached 57% of the ocean in 2019, the last year measured in the study. By comparison, only 2% of the ocean surface saw such extreme temperatures 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.

This “new normal” of extreme heat across the majority of the ocean’s surface highlights the urgent need for humans to dramatically curb greenhouse gas emissions from fossil fuel production, the main driver of climate change, researchers warned.

Scientists have warned the world has already warmed about 1.1 degrees Celsius above preindustrial levels and is on track to see global temperatures rise 2.4 degrees Celsius by the end of the century.

Global ocean temperatures have warmed every year since 1970, and marine ‘heatwaves’ have doubled in frequency and have become longer and more intense, according to a 2019 special report by the Intergovernmental Panel on Climate Change.

Rapid ocean warming, which has prompted a drop in fish populations across the world, threatens coastal communities, fishing economies and those in polar and high mountains regions.

“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,” Van Houtan said.