95% of existing ocean climates could disappear by 2100 if CO2 emissions continue to climb

A new study published in the journal Nature suggests that our oceans' climates — existing environments with delicately balanced ecosystems — face extreme change under two climate-change scenarios.

Coral, shelled organisms face new threats as climate warms

Colourful coral reef with many fishes and sea turtle
A new study suggests that, unless CO2 is drastically cut, Earth's oceans could lose 95 per cent of their existing climates. (Shutterstock/stockphoto-graf)

Canada is home to three oceans, all of which harbour thousands of fish and animals, on which many Canadians rely. But, with a warming planet, these bodies of water are rapidly changing.

A new study published in the journal Scientific Reports suggests that our oceans' climates — existing environments with delicately balanced ecosystems — face extreme change under climate-change scenarios.

When trying to predict how our climate will change as a result of increased greenhouse gas emissions, scientists use something called the representative concentration pathway, or RCP. They represent different climate futures under varying levels of greenhouse gas emissions. 

In this study, the authors looked at two: RCP 4.5 and RCP 8.5.

Under RCP 4.5 — considered a moderate scenario — emissions peak in 2050, and are then followed by a slowed decrease. Under RCP 8.5 — often considered as a "business-as-usual" scenario, and the worst one — emissions peak in 2100 and are then followed by a slowed decrease. 

Under these scenarios, the authors suggest that 10 to 85 per cent of the surface ocean would see conditions never before seen, or a change in their "climate."

But under the RCP 4.5 scenario, 35.6 per cent of surface ocean climates may disappear altogether by 2100. Under RCP 8.5, that rises to 95 per cent. 

"Previous studies have looked at specific locations and said, 'Okay, this location's getting warmer, or this location is getting acidic.' What we did was, we looked at the whole climate of the global ocean," said lead author Katie Lotterhos, associate professor of marine and environmental sciences at Northeastern University's Marine Science Center in Nahant, Maine.

Yellow and light brown coral is seen in murky ocean waters.
This photo of the coral on Australia's Great Barrier Reef — Earth's largest living structure — shows a bleaching event, where small organisms leave it due to a rise in temperature. Coral like this one are threatened with an increase in ocean temperature and acidification. (William West/AFP/Getty Images)

When they looked at the ocean climates of today compared to 1800, they didn't see any emergence of "novel" climates or climates that had never been seen before. There were certainly changes, but nothing that was brand new. 

But the same couldn't be said about looking toward the future.

"When you look from today through 2100, depending on the climate-change scenario, and under more extreme climate change scenarios, a higher proportion of the ocean surface is going to experience these novel climates," Lotterhos said.

And this has dire consequences for the organisms that reside in our vast oceans.

Double whammy

As we produce more CO2, a lot of it is trapped in the atmosphere. However, our oceans actually absorb the majority of it. 

A report released by the National Oceanic and Atmospheric Administration (NOAA) this week found that in 2020, the ocean absorbed roughly three billion tonnes more CO2 than what was released, the highest amount since the start of records began in 1982 and roughly 30 per cent higher than the average over the past two decades.

And that changes the ocean's structure. Not only do our oceans warm, but the greater CO2 absorption also changes pH levels. This change is what is referred to as ocean acidification. 

The Nature study examined the level of pH, or acidity, and something that is called a saturation state, which relates to how difficult it is for organisms to make their shells. 

They found that under the RCP 4.5 and RCP 8.5 scenarios, the ocean surface will become more acidic with a lower saturation of aragonite, which is a mineral used by corals and other marine organisms to form shells. 

Just as we require calcium to make our bones, so do shelled organisms. They get this from seawater, but with ocean acidification, calcium becomes less available and hydrogen becomes more common. 

And that presents a double whammy for organisms: it becomes harder to form their shells, and it also becomes more difficult to keep what shells they have from dissolving back into the seawater.  

A man lowers a lobster trip to another man standing in a boat.
Canadians who rely on the oceans for survival face changes as the oceans warm. (CBC)

Denis Gilbert, a research scientist on climate and ocean physics at the Department of Fisheries and Oceans, and part of the Intergovernmental Panel on Climate Change's (IPCC) Working Group I, who was not involved in the new study, said that the findings are concerning, though he wouldn't refer to it as a changing ocean climate, but rather a changing ocean chemistry.

"I was surprised to see that by 2100, there was that much of the ocean that had an entirely different climate, either entirely novel or an entirely extreme [climate]," he said. "But I find the usage of the word climate a bit unfortunate … If the authors had chosen the word chemistry or chemistries, it would better reflect what the paper is actually saying."

He noted that while they do discuss ocean temperature, the main thing they address is the pH and saturation levels, which is the changing chemistry.

"The bottom line is that they're concerned with what's going to happen to the shells of certain animals that calcify with aragonite," he said. 

Winners and losers

However, Lotterhos noted that it doesn't mean that all shelled organisms — or those that depend on them — are doomed. 

"We often talk about winners and losers … in terms of species, but there are a lot of emerging studies that show there are also winners and losers within species," Lotterhos said. "And that indicates that there's some genetic variation for which evolution can act on. So there is a lot of hope in the sense that there is genetic variation and a lot of marine species for which evolution can act on and that gives me hope that species will be able to persist in the future."

And while ocean acidification is rising around the globe, the study suggests that three regions will see the greatest change in novel climates first: the Indo-Pacific, Arctic and Antarctic. 

But that's not to say that Canadians who depend on the oceans for their livelihoods won't see changes. 

Canada's Changing Climate Report, released by the federal government in 2019, found that the Pacific Northwest, for example, will experience more CO2 and lower pH in the coming decades.

And the Arctic, which is often considered as the pulse of climate change as it warms at twice the rate of the rest of the world — in some places almost four times as much — is experiencing rapid increases in freshwater from melting ice. This, in turn, has reduced the aragonite saturation rate making shelled organisms particularly vulnerable. 

But Lotterhos noted that the two different scenarios illustrate that if we make changes and reduce CO2 emissions, it can have a huge impact. 

"Humans are slow learners and climate is changing faster than our systems for regulation in management can keep up," she said. "And so as long as we're in this pile of bureaucracy, where we can't adapt our social systems and our management systems to the speed at which climate is changing, it's going to exacerbate climate change even more so."


Nicole Mortillaro

Senior reporter, science

Based in Toronto, Nicole covers all things science for CBC News. As an amateur astronomer, Nicole can be found looking up at the night sky appreciating the marvels of our universe. She is the editor of the Journal of the Royal Astronomical Society of Canada and the author of several books. In 2021, she won the Kavli Science Journalism Award from the American Association for the Advancement of Science for a Quirks and Quarks audio special on the history and future of Black people in science. You can send her story ideas at