Things got really strange in the waters off of Southern California in 2015.
Pacific Ocean temperatures jumped as much as 10 degrees Fahrenheit above average, as an unprecedented warming trend stretched from Alaska to Mexico.
It was a bonafide marine heat wave.
In a study published Tuesday in the journal Nature Communications, researchers concluded that since 1925, the number of marine heat wave days increased by over 50 percent annually, and the frequency of the events increased by nearly 35 percent. And our warming climate could be to blame.
As oceans soak up heat from a warming Earth, average ocean temperatures have been ticking up, making it easier for extreme marine heating events to occur.
During the greater heat wave event that caused the event off the coast of Southern California, a number of sea-dwelling creatures, including sea lions, birds, and quite possibly nearly 50 whales, died.
Unlike heat waves on land, however, marine heat waves absorb far more heat than the air, resulting in long-lived extremes.
“Sometimes heat waves in the ocean can be very long,” Emanuele Di Lorenzo, a marine scientist at the Georgia Institute of Technology’s School of Earth & Atmospheric Sciences who had no involvement in the study, said in an interview.
Di Lorenzo cites the 2014-2015 “warm blob” event in the Pacific Ocean, which lasted over a year.
“That opened everybody’s eyes,” said Di Lorenzo. “And, of course, you have massive implications for living things.”
When the oceans cook, the consequences for sea creatures is likely similar to that of terrestrial heat waves for people.
Terrestrial heat waves “tend to be the most deadly of all weather phenomena,” said Bill Patzert, a former NASA climatologist at the Jet Propulsion Laboratory who was not involved in the study. He cites Europe’s infamous 2003 heat wave, which killed about 70,000 people.
Marine heat waves, however, aren’t nearly as well-documented, but are already known to be devastating, said Patzert. For example, extreme heat waves have repeatedly hit the Great Barrier Reef, northeast of Australia. In 2016, such a heating event contributed to the die-off of nearly 70 percent of shallow-water corals in a 430-mile area of the most pristine reef.
In this case, a marine heat wave exacerbated already abnormally high ocean temperatures. Vast swathes of stressed coral were essentially kicked when they were already down.
“It’s a compounded pain,” said Di Lorenzo.
In the study, the researchers attributed these increasing heat wave trends to the rising average of global ocean temperatures. Warmer oceans simply make it easier for temperatures to jump to such extreme levels.
“This means that you’ll have times where you’ll have a higher chance of reaching heating thresholds,” said Di Lorenzo.
Although the study’s researchers reached back to sea surface temperature data from over a century ago, the best data comes after 1982, said Di Lorenzo. Specifically, this means the inclusion of satellite data collected by National Oceanic and Atmospheric Administration (NOAA) satellites over the course of over 30 years.
“There is no question that there’s a trend,” said Di Lorenzo of the increase in duration and frequency of marine heat waves. But he cautions that this data set (1982-2016) covers too short a time period to say that the uptick in heat waves is due to climate change. The increase in observed heat waves might actually be due to natural temperature swings in the ocean, as opposed to a consequence of global warming.
That said, it is clear that the average temperature increase measured in oceans today is inarguably caused by human-induced climate change. Around 95 percent of the sun’s radiation that gets trapped in the atmosphere is absorbed by the oceans.
“The unequivocal proof of global warming is ocean warming — it’s pretty simple,” said Patzert.
Extreme warming events in the ocean will be especially likely to occur around longer-term warming trends that can last years or longer, said Patzert. This includes El Niño events in the Pacific Ocean, and the longer-term Pacific Decadal Oscillation, which can warm vast regions of the Pacific Ocean for decades.
“In some ways the extreme events in ocean, like on the land, can be more punishing than slower moving events,” said Patzert. Oceans are already suffering from pollution and overfishing. “So, when you pile it on with these marine heat waves, then it just exacerbates the situation. It makes it more devastating.”
Ocean temperatures will almost certainly continue to rise this century. Though, if there’s a sustained global effort to mitigate the release of potent greenhouses gases into the atmosphere, the severity of the rise could be limited.
In the U.S., however, government attempts at shifting from fossil fuels burning to renewable energies like solar have been blocked by the beleaguered head of the Environmental Protection Agency, Scott Pruitt. Pruitt hopes to repeal the Clean Power Plan, President Obama’s plan to wean the nation off of heat-trapping fossil fuels.
“We’re living in a warmer world, and we’re exacerbating it,” said Patzert.