'Surprise' Ocean Heat Waves Are Becoming More Common

Illustration for article titled 'Surprise' Ocean Heat Waves Are Becoming More Common
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There are two flavors of surprise: good and bad. Winning the lottery? Good. Extreme heat waves cooking the oceans with more regularity, ruining fisheries that millions of people rely on? Decidedly bad.


Yet that’s our present predicament, one that’s likely to get worse as the oceans heat up even further. A new study released in the Proceedings of the National Academy of Sciences on Monday shows that climate change is already pushing large portions of the oceans outside their normal bounds, resulting in what the authors call “surprise” conditions that can wreak havoc on fisheries and the livelihoods associated with them. Climate change could further push ecosystems outside their limits, forcing the people who rely on them to adapt or suffer the consequences.

To undertake their study, researchers dug into annual temperature data for 65 large marine ecosystems collected since 1900. They then compared a given year to the 30 years preceding it, basically making a running average of “normal” conditions. Years where the temperature was two standard deviations warmer (or colder) than the preceding 30 years was dubbed a “surprise.” The two standard deviation mark is also dubbed a “significant” threshold in science, but surprise is a much more common way to think about it.

“I wondered what would happen if you allow the reference points to shift as new information comes in,” Andrew Pershing, the chief science officer at the Gulf of Maine Research Institute who led the study, told Earther. “This led us down a path toward thinking about how ecosystems and people will adjust to warmer conditions, and what rate of change will be really stressful.”

The results show a dramatic upswing in surprising years since the 1980s, particularly in the Arctic and Atlantic. Those surprises are largely of the hotter-than-normal variety. Only four cold surprises have occurred since 2000. The pace of hot surprises appears to have accelerated since 2010 in the Pacific and Indian oceans as well. There are certain natural climate shifts that have driven the heat, notably the Super El Niños that hit in 1997 and 2015-16. But climate change has created a heat bender in the oceans, making oceanic heat waves more likely (a similar trend has been observed on land).

“I was, ahem, surprised that allowing the definition of an extreme event to change as conditions warm did not decrease the number of extreme events as much as I expected,” Pershing said. “I was also surprised by how wide-spread these surprising temperatures are.”


The surprise conditions at sea can ruin livelihoods on land (to say nothing of the ecosystems they hit). Pacific crab fisheries have been rocked by a persistent blob of abnormally hot water in recent years while the Gulf of Maine—a place among the fastest-warming regions on Earth—has seen its lobster industry get hit hard by extreme heat events.

The new findings show that freakishly hot ocean waters will only become more common in the coming decades. Rising heat could almost make these surprise conditions the norm, with the study noting many of the 65 areas studied could see odds approaching a “theoretical maximum” of surprise oceanic heat waves if the world continues emitting carbon dioxide like there’s no tomorrow. So uh, we should probably not do that.


Even if carbon pollution gets reined in, it’s clear the fisheries are operating in a different environment than the one they have grown to rely on. The study recommends that policymakers use on these and other findings around extreme conditions to provide more support for fisheries and the people who work in them. That could mean coming up with improved seasonal forecasts, setting tighter catch rates, providing better insurance options to help protect against losses, and  improving conservation practices to ensure the marine species that have to live in the hot water don’t go belly up, too.

Managing editor at Earther, writing about climate change, environmental justice, and, occasionally, my cat.


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On ocean heat from our friends at NOAA: Global Climate Dashboard www.climate.gov 

The first graph below is essentially the amount of heat (energy) loss or gain with respect to a 1955 to 2006 average for the top half mile of the ocean. For the past several years about 15 x 10^22 joules or 3.6 x 10^13 tons TNT of heat energy accumulated each year.

The other graphs are global CO2 concentration and temperature. Everything keeps trending up.