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Marine Heatwaves Now Longer, Hotter and More Intense

Climate
Record-setting bloom of toxic algae in North Pacific in 2015. NOAA

It's not just land-based heatwaves that have become more intense and frequent. Marine heatwaves are similarly on the rise as a direct result of warming oceans, according to a new international study.

The research, published Tuesday in the journal Nature Communications, shows that from 1925-2016, the frequency of marine heatwaves increased on average by 34 percent and the length of each heatwave increased by 17 percent. In all, the number of marine heatwave days has increased 54 percent per year.


These bursts of ocean heat can have widespread effects on underwater ecosystems, marine life and coastal communities.

As a press release for the study detailed, a 2011 marine heatwave in Western Australia shifted ecosystems from being dominated by kelp to being dominated by seaweed. That shift remained even after water temperatures returned to normal.

Then in 2012, a marine heatwave in the Gulf of Maine caused an increase in lobsters but resulted in a crash in prices that seriously hurt the industry's profits.

Warm waters in the North Pacific from 2014-2016 led to fishery closures, mass strandings and harmful algal blooms along coastlines. In 2015, the U.S. West Coast's mysterious "blob" of water, up to 4°C warmer than the surrounding Pacific, became tied to unusual weather across the country.

Another intense marine heatwave in 2016 off Tasmania led to disease outbreaks and impacted the region's oyster and salmon industries.

"Our research also found that from 1982 there was a noticeable acceleration of the trend in marine heatwaves," said lead author Dr. Eric Oliver, a researcher at Dalhousie University in Canada.

"While some of us may enjoy the warmer waters when we go swimming, these heatwaves have significant impacts on ecosystems, biodiversity, fisheries, tourism and aquaculture. There are often profound economic consequences that go hand in hand with these events."

The researchers combined satellite data with a century-long range of datasets, taken from ships and various land-based measuring stations, to determine the trend of intensifying marine heatwaves. They eliminated natural warming variables caused by the El Niño Southern Oscillation, the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation to come to their conclusion.

"There was a clear relationship between the rise in global average sea-surface temperatures and the increase in marine heatwaves, much the same as we see increases in extreme heat events related to the increase in global average temperatures," said co-author and University of New South Wales scientist Dr. Lisa Alexander.

"With more than 90 percent of the heat from human-caused global warming going into our oceans, it is likely marine heatwaves will continue to increase. The next key stage for our research is to quantify exactly how much they may change," she said.

"The results of these projections are likely to have significant implications for how our environment and economies adapt to this changing world."

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"Faced with global warming, rising sea levels, and the climate-related extremes they intensify, the question is no longer whether some communities will retreat—moving people and assets out of harm's way—but why, where, when, and how they will retreat," the study begins.

The researchers suggest that it is time to rethink retreat, which is often seen as a last resort and a sign of weakness. Instead, it should be seen as the smart option and an opportunity to build new communities.

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"There's a definite rhetoric of, 'We're going to build it back better. We're going to win. We're going to beat this. Something technological is going to come and it's going to save us,'" said A.R. Siders, an assistant professor with the disaster research center at the University of Delaware and lead author of the paper, to the New York Times. "It's like, let's step back and think for a minute. You're in a fight with the ocean. You're fighting to hold the ocean in place. Maybe that's not the battle we want to pick."

Rethinking retreat could make it a strategic, efficient, and equitable way to adapt to the climate crisis, the study says.

Dr. Siders pointed out that it has happened before. She noted that in the 1970s, the small town of Soldiers Grove, Wisconsin moved itself out of the flood plain after one too many floods. The community found and reoriented the business district to take advantage of highway traffic and powered it entirely with solar energy, as the New York Times reported.

That's an important lesson now that rising sea levels pose a catastrophic risk around the world. Nearly 75 percent of the world's cities are along shorelines. In the U.S. alone coastline communities make up nearly 40 percent of the population— more than 123 million people, which is why Siders and her research team are so forthright about the urgency and the complexities of their findings, according to Harvard Magazine.

Some of those complexities include, coordinating moves across city, state or even international lines; cultural and social considerations like the importance of burial grounds or ancestral lands; reparations for losses or damage to historic practices; long-term social and psychological consequences; financial incentives that often contradict environmental imperatives; and the critical importance of managing retreat in a way that protects vulnerable and poor populations and that doesn't exacerbate past injustices, as Harvard Magazine reported.

If communities could practice strategic retreats, the study says, doing so would not only reduce the need for people to choose among bad options, but also improve their circumstances.

"It's a lot to think about," said Siders to Harvard Magazine. "And there are going to be hard choices. It will hurt—I mean, we have to get from here to some new future state, and that transition is going to be hard.…But the longer we put off making these decisions, the worse it will get, and the harder the decisions will become."

To help the transition, the paper recommends improved access to climate-hazard maps so communities can make informed choices about risk. And, the maps need to be improved and updated regularly, the paper said as the New York Times reported.


"It's not that everywhere should retreat," said Dr. Siders to the New York Times. "It's that retreat should be an option. It should be a real viable option on the table that some places will need to use."

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