Dire ocean scenario warns of the effects of climate change

Essential nutrients could become trapped in the Southern Ocean.

By Chris Mooney / The Washington Post

Scientists on Thursday published an alarming scenario for what could happen to the planet’s oceans and fisheries by the year 2300 if very high levels of global warming are allowed to continue.

The good news is that it’s eminently avoidable, and a very long way off from happening. The bad news is that, according to the concerned authors, it highlights a new vulnerability that could arise in a severely disrupted climate system — and becomes a real possibility if rampant global warming continues well beyond this century.

The study finds that in a future world of extreme warming, after Antarctic sea ice collapses and oceans are altered, large volumes of essential nutrients could become trapped in the Southern Ocean. That could impair the growth of tiny marine organisms that form the base of the food chain in other parts of the world’s oceans, thus triggering a 20 percent decline in fishery yields overall, including a 60 percent drop in the Atlantic.

This would occur because the Southern Ocean near Antarctica is a key site of “upwelling,” in which deep ocean waters, which have picked up such nutrients as phosphorous and nitrogen from the depths (which end up there after marine organisms die and their bodies sink), rise up and deliver that biological bounty to the surface. Then, the nutrients enter the global ocean circulation and are carried northward to more moderate climes.

But if warming gets severe enough, Southern Ocean upwelling can be suppressed by warm ocean surface waters. Meanwhile, many of the nutrients that do manage to rise will be consumed by the increasingly active biology of the mostly ice-free ocean around Antarctica — leaving far fewer nutrients for the rest of the world.

In this case, as organisms in the Southern Ocean die, more nutrients again sink to the bottom of that ocean, and stay there.

“So you have nutrients building up in the deep ocean, down where the biology can’t use them or get to them,” said Keith Moore, the lead author of the study in Science, and a professor at the University of California, Irvine.

The researchers concede that the picture they paint is dire — and requires very high levels of warming that might never materialize. The temperature of the Antarctic ocean in the scenario, for instance, would be 10.8 degrees Fahrenheit warmer than it is now, and the sea ice ringing Antarctica would be almost entirely gone.

The computer modeling study also uses a worst-case scenario for the burning of fossil fuels to the year 2100 and even beyond it, ultimately triggering atmospheric concentrations of carbon dioxide just below 2,000 parts per million. That’s far in excess of the current level around 410 parts per million. It’s questionable that humanity would let things get that bad, and growing numbers of wind and solar installations and electric cars suggest that in future decades we’ll be powering key aspects of life without fossil fuels.

Still, the authors said it’s worth probing such extremes to understand how the climate system works, and noted that for now, a high emissions scenario remains possible.

“These simulations paint a fairly dire picture of what I think will be catastrophic changes in the context of unmitigated climate warming,” said Matthew Long, one of the study’s authors and an oceanographer at the National Center for Atmospheric Research in Boulder, Colorado. “Along the path to those very catastrophic events, we may cross thresholds that we don’t know about. And so, I think it’s important for people to reflect on the impact we’re having on the world’s ocean and consider that in the context of action to mitigate climate warming.”

A researcher who was not involved in the study but reviewed it for The Washington Post, oceanographer Lynne Talley of the Scripps Institution of Oceanography, said she found the scenario plausible, if warming is strong enough.

“Maybe they’ve got an extreme answer here, but all the pieces are what you’d expect to happen in a more moderate forcing,” Talley said.

An accompanying essay in Science, by ocean experts Charlotte Laufkotter and Nicolas Gruber of the University of Bern and ETH Zurich, respectively, in Switzerland, added that “the mere possibility of a future Southern Ocean nutrient-trapping scenario is highly concerning, warranting dedicated efforts to further our understanding of the unique role of the Southern Ocean in the global climate system.”

Fortunately, the study assumes as its premise a level of global warming that we in the present have ample opportunity to prevent.

If you think that the Paris climate agreement will ultimately work, holding the warming of the planet to “well below” 3.6 degrees Fahrenheit and bringing atmospheric carbon dioxide concentrations back down before they get much past 450 parts per million, then you can safely assume that such things will not occur.

On the other hand, if you don’t think the world can manage economic and population growth in the coming decades without a continual or even growing reliance on fossil fuels, this extreme scenario may be hard to get out of your mind.

Moore also said that he thinks the scenario presented in the study could at least begin to kick in at a lower temperature than the extreme ones in the paper. He said he’ll start to worry at a global temperature rise around 4.5 degrees Fahrenheit, which is when a lot of floating Antarctic sea ice could start to go.

“We don’t know exactly where that tipping point is,” Moore said. The study thus reinforces the importance of the Paris climate goals.

In the end, Long argued that there is a value in describing what the worst-case scenario actually is — even if it is never actually realized.

“Human-driven climate warming is driving changes in the ocean that are epic in the context of Earth history,” he said. “They’re commensurate with some of the biggest, most fundamental reorganizations of the life support system of the planet. The scenario is unlikely, yet action remains stalled.”

Talk to us

More in Nation-World

A passenger aircraft at Ciudad Real International Airport in Ciudad Real, Spain, on Oct. 27, 2020. MUST CREDIT: Bloomberg photo by Paul Hanna.
Airlines face ‘mission of the century’ in shipping vaccines

Cars, buses, trucks, motorcycles, bikes and even donkeys may be needed to get the drug to rural areas.

Dr. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, speaks during a news conference with the coronavirus task force at the White House in Washington, Thursday, Nov. 19, 2020. (AP Photo/Susan Walsh)
Fauci: US may see ‘surge upon surge’ of virus in weeks ahead

He does not expect current recommendations around social distancing to be relaxed before Christmas.

FILE - Election workers, right, verify ballots as recount observers, left, watch during a Milwaukee hand recount of presidential votes at the Wisconsin Center, Friday, Nov. 20, 2020, in Milwaukee. Wisconsin finished a partial recount of its presidential results on Sunday, Nov. 29, 2020 confirming Democrat Joe Biden's victory over President Donald Trump in the key battleground state. Trump vowed to challenge the outcome in court. (AP Photo/Nam Y. Huh)
Completed Wisconsin recount confirms Biden’s win over Trump

Dane County was the second and last county to finish its recount, reporting a 45-vote gain for Trump.

FILE - This Nov. 18, 2020, file photo provided by the Utah Department of Public Safety shows a metal monolith in the ground in a remote area of red rock in Utah. The mysterious silver monolith that was placed in the Utah desert has disappeared less than 10 days after it was spotted by wildlife biologists performing a helicopter survey of bighorn sheep, federal officials and witnesses said. The Bureau of Land Management said it had received credible reports that the three-sided stainless steel structure was removed on Nov. 27.  (Utah Department of Public Safety via AP, File)
Mysterious silver monolith disappears from Utah desert

It vanished less than 10 days after it was spotted by wildlife biologists from a helicopter.

FILE - In this Tuesday, June 20, 2017 file photo a Boing 737 MAX 9 airplane performs a demonstration flight at the Paris Air Show, in Le Bourget, east of Paris, France. Europe’s aviation regulator has taken a step closer to letting the Boeing 737 Max fly again. It published a proposed airworthiness directive on Tuesday that could see it clear the aircraft within weeks to resume flying after nearly two years and a pair of deadly crashes. (AP Photo/Michel Euler, file)
European regulator moves to clear Boeing 737 for flight

The move comes after the FAA already cleared the Boeing 737 Max earlier this month.

FILE - This May 5, 2019, file photo shows Alex Trebek gestures while presenting an award at the 46th annual Daytime Emmy Awards in Pasadena, Calif. Jeopardy!” host Alex Trebek died Sunday, Nov. 8, 2020, after battling pancreatic cancer for nearly two years. Trebek died at home with family and friends surrounding him, “Jeopardy!” studio Sony said in a statement. Trebek presided over the beloved quiz show for more than 30 years. (Photo by Chris Pizzello/Invision/AP, File)
Alex Trebek, ‘Jeopardy’ host and trivia master, has died at 80

He had suffered a series of medical complications in recent years, and died at his home.

Weekly COVID-19 infections in nursing homes in 20 states have been rising since May. (AP Graphic)
Nursing home COVID-19 cases rise four-fold in surge states

Resident deaths more than doubled, according to study by University of Chicago health researchers.

Democratic presidential candidate former Vice President Joe Biden speaks to supporters, early Wednesday, Nov. 4, 2020, in Wilmington, Del. Biden defeated President Donald Trump to become the 46th president of the United States on Saturday, positioning himself to lead a nation gripped by historic pandemic and a confluence of economic and social turmoil. (AP Photo/Paul Sancya)
The vote is in: Joe Biden to become 46th president of U.S.

The victory comes after days of uncertainty as election officials sorted through a surge of mail-in votes.

Republican candidate for Senate Sen. David Perdue speaks during a campaign stop at Peachtree Dekalb Airport Monday, Nov. 2, 2020, in Atlanta. The outcome in several contested states will determine whether Joe Biden defeats President Donald Trump. But if the Democratic challenger wins, the ambitions of a Biden presidency could well come down to Georgia. (AP Photo/John Bazemore)
Twin Senate runoffs in Georgia could shape Biden presidency

Should Democrats win them, Biden would would increase his chances for passing legislation.

Democratic presidential candidate former Vice President Joe Biden joined by Democratic vice presidential candidate Sen. Kamala Harris, D-Calif., speaks at the The Queen theater Thursday, Nov. 5, 2020, in Wilmington, Del. (AP Photo/Carolyn Kaster)
Biden on cusp of presidency after gains in Pennsylvania

Trump is testing his presidential powers in undermining America’s confidence in the vote.

People demonstrate outside the Pennsylvania State Capitol to urge that all votes be counted, Wednesday, Nov. 4, 2020, in Harrisburg, Pa., following Tuesday's election. (AP Photo/Julio Cortez)
Biden pushes closer to victory in race for the White House

To win, Trump would need to win Pennsylvania, North Carolina, Georgia and Nevada.

FILE—John Hickenlooper, Democratic candidate for the U.S. Senate seat in Colorado, speaks during a car rally for Doug Emhoff, husband of Democratic vice presidential candidate Kamala Harris, at East High School late Thursday, Oct. 8, 2020, in Denver. More than 70 motorists took part in the rally to urge people to get out and vote in the upcoming election. (AP Photo/David Zalubowski, File)
Democrats losing paths to Senate control as GOP hangs on

Several races remained undecided into Wednesday and at least one headed to a runoff in January.