Our oceans are hotter than ever. Scientists say they worry about what that means for our future

The world's oceans have been getting warmer every year for the past seven. They're now hotter than they've ever been in recorded history. And the changes are already taking a toll on marine life.

Species such as coral, oysters and crabs are struggling after seven years of record ocean heat

A diver photographs golden anthias (Pseudanthias aurulentus) on a coral reef in the Egyptian Red Sea marine reserve of Ras Mohamed, off the southern tip of the Sinai Peninsula, in September 2018. (Emily Irving-Swift/AFP/Getty Images)

Our planet is changing. So is our journalism. This story is part of Our Changing Planeta CBC News initiative to show and explain the effects of climate change and what's being done about it.

Amid another record warm year for the planet, one of the most dramatic and alarming changes occurred in our oceans, according to the National Oceanic and Atmospheric Administration (NOAA). 

They are the warmest they've been in recorded history.

In fact, the ocean heat has been topping its own record annually for the past seven years, with last year's record set despite the absence of El Niño — a warming in part of the Pacific Ocean that tends to drive up global temperatures.

While many Canadians — most of whom are land-locked — may not be focused on the state of our world's oceans, people across the globe will be affected by the changes happening in them: species of marine life moving out of their typical regions and into others, creating an imbalance in aquatic life; a rise in sea levels; warmer waters that can add fuel to already powerful hurricanes and changes in our food webs. 

'Not just a future scenario'

Our oceans are in a "new normal," concluded a study published in the journal PLOS Climate this month that found 2014 was the first year the world's oceans exceeded the 50-per-cent threshold of extreme heat.

"We need to understand that climate change is really not just a future scenario," said Kisei Tanaka, a marine biologist with NOAA and lead author of the study. "It's something that's happening as we speak. And it has been happening for some time."

These changes, mostly seen in the form of marine heat waves — think of what happened off the coast of B.C. during last summer's heat wave where a billion marine creatures were killed — aren't spread out uniformly across the world's oceans, but are more pronounced in parts of the North Atlantic and the Indian Ocean. 

However, they are increasing in frequency — and are already taking their toll on marine life.

Footage captured on June 27, 2021, near Third Beach in Vancouver shows thousands of mussels that died during B.C.'s heat wave. (Chris Harley/University of British Columbia)

As is typical with climate change, it's the people in the north who are seeing the most rapid alterations to their way of life.

"What you're going to see over time is that parts of the Arctic Ocean will begin to look like Pacific and Atlantic oceans and the species, the ecosystems that thrive here, you're going to see their numbers decrease," said Hilu Tagoona, a senior Arctic adviser for Oceans North, a charitable organization that supports marine conservation together with Indigenous and coastal communities.

"And that's already being seen. Over the last 25 years, the species that typically thrive here, the numbers are going down."

Cascading effects

Our oceans store about 90 per cent of our planet's heat. But that energy won't stay trapped forever. And when it is released over time, it means our atmosphere will warm even more.

Tim Boyer, an oceanographer with NOAA's National Centers for Environmental Information, said it's hard to quantify just how much of a difference it would make if our oceans released their heat energy.

But, he put it like this: "If the top 1,000 metres of the ocean were suddenly to drop in temperature to 0.1 C, and that heat was released to the atmosphere, the atmosphere would see an increase of 100 C in temperature."

Of course, the ocean wouldn't just suddenly release that energy back into the atmosphere at once, he said. But it's a way of illustrating just how much of a difference a small percentage makes.

This chart shows ocean heat content in the upper 2,000 metres since 1958, with zero being the annual mean. Our oceans are trapping an enormous amount of heat. (Cheng, et. al)

A study co-authored by Boyer, and published in the journal Advances in Atmospheric Sciences in January, found the heat content in the upper 2,000 metres of our oceans has been steadily increasing since 1958 with a noticeable increase since the 1980s.

As a result, our oceans have increased in acidity  — a process called ocean acidification — and have also seen more ocean stratification, where the water is prevented from mixing due to its different properties, including its density. This can result in less oxygen for marine life at greater depths. 

Ocean species struggling

Carbon dioxide (CO2) dissolves in seawater. But because of increasing CO2 in our atmosphere due to human activities, more CO2 is dissolving, which decreases the ocean's pH. 

Acidity is measured on a pH scale that runs from 0 to 14.  Anything lower than 7 is considered acidic. Currently, the average ocean pH is roughly 8.1, 30 per cent more acidic than it was 200 years ago.

As a result, species such as coral, oysters and crabs that depend on the ocean carbonate ions and calcium to build their skeletons are struggling. 

A pteropod shell is shown dissolving over time in seawater with a lower pH. When carbon dioxide is absorbed by the ocean from the atmosphere, the chemistry of the seawater is changed. (NOAA)

"When a small animal that has a shell to it, let's say an oyster, when it is in the larval stage, it tries to build these layers, just like a little tree tries to build bark on it," Peter Chandler, a physical oceanographer with the Fisheries and Oceans Canada, said.

"Anything that makes that difficult, keeps it exposed to anything that wants to eat it…  If you have difficulty forming that shell, you stay vulnerable for longer. Sometimes you may not be able to form it at all."

If there's a decrease in these marine organisms, other marine life that rely on them as a food source can't get enough. Consequently, humans who depend on the fish as a source of food may not be able to find them in their traditional areas.

This is happening now in some parts of the world.

Boats are loaded with traps in Eastern Passage, N.S. on Tuesday, Nov. 30, 2021. (Andrew Vaughan/The Canadian Press)

The effects of our warming oceans are already being seen along coasts around the world. Heat that is stored in our oceans cause the water to expand, which, according to NASA, is already responsible for one-third to one-half of sea level rise, threatening coastal communities.

There are other far-reaching effects that threaten our everyday lives.

"You also have that increased heat in the ocean that affects weather patterns, that affects hurricane generation, for instance," Chandler said. "It's much easier if you have a warm Gulf of Mexico to have a much more highly intensive hurricane coming through, because the heat energy for a hurricane is coming from the ocean."

Our oceans make up four fifths of the planet, which is why keeping them healthy is important to the overall health of Earth, Chandler said.

"If we really put a lot of thought and a lot of effort and a lot of awareness into keeping the oceans healthy, the rest of the planet is going to be four fifths of the way there," Chandler said.


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