Last year was a record-breaker for the global temperature but 2023 also saw new heat records set in our oceans. And as one climate scientist noted, ‘The oceans are the most important thing.’
Oceans absorb 90% of Earth’s excess heat. That will have long-term consequences
Nicole Mortillaro · CBC News
· Posted: Jan 18, 2024 4:00 AM EST | Last Updated: January 19
In 2023, Earth’s oceans were the warmest they’ve been in recorded history. Scientists say oceans might be a bigger climate indicator than has been realized. (Shutterstock/Tatiana Popova)By now, most people are well aware that 2023 was the hottest year on record, coming in at 1.48 C warmer than the pre-industrial average from 1850-1900. This beat out 2016’s record of 1.25 C.
In climate terms, an increase in warming by 0.23 C is considerable and climate scientists are still trying to figure out why it happened.
Was 2023 just a big blip on the upward trend of global warming? Perhaps. Scientists are trying to tease out all the potential contributors.
But one of the things that is inarguably a contributor is the continued warming of our oceans
Last year, our oceans were the hottest on record. It was the first year in which the average global sea surface temperatures (SST) — that is, temperatures of the upper metre of water — surpassed 1 C compared to pre-industrial levels.
Then there’s the ocean heat content (OHC), which is the temperature 2,000 metres below the surface. That, too, was at a record high in 2023. And this is of particular concern because OHC is a critical climate indicator. Our oceans, which cover more than 70 per cent of the planet, store more than 90 per cent of Earth’s excess heat.
Just how much heat did our oceans take in last year?
To put it in perspective, Zeke Hausfather, a research scientist at Berkeley Earth, a non-profit, independent climate analysis organization, said that we added 15 zettajoules of energy to the oceans compared to 2021. That’s the equivalent to a billion trillion joules — or the equivalent of 25 times of all the energy used by humanity.
“It’s a pretty mind–bogglingly big number,” he said.
And that ocean heat content is continually rising. The more CO2 we pump into the atmosphere, the more the oceans will absorb.
We may be forgiven for not paying as much attention to the oceans as we should. After all, as human beings, we look at global heat as it occurs on the surface because that’s where we live, that’s what we experience.
But for climate scientists, the oceans are a critical indicator.
“For climate scientists who think about the climate system as a whole … the oceans are the most important thing,” said Simon Donner, a climate scientist and professor at the University of British Columbia. “It’s because they cover two–thirds of the planet, they’re very deep and they’re made up of water, not air. And water has got a high heat capacity.
“So they are like the planet’s great heat sink.”
Looking at 2023Taking a look at just the oceans, there were many different contributors to 2023’s record heat.
First, there was an El Niño. Though it wasn’t a super event, as it was in 2015-16, it’s still been fairly significant. This warming of the central Pacific Ocean tends to produce an increase in the global temperature. But typically there is a lag, meaning the warmer temperatures aren’t seen until the year following the start of an El Niño.
“This year has been unusual, even for an El Niño. If we look at right now, globally, [the SST is] about … 21.0. C. By SST data, that’s about 0.2 C above where we were at this time in 2016, which is the last big El Niño event,” said Hausfather. “And 2016 was, to be honest, a much bigger El Niño event. And so you know, a 0.2 C increase relative to then in eight years is a little worrying.”
But Hausfather and Donner believe part of this may have been because we came from a “triple-dip” La Niña, the little sister to El Niño where ocean temperatures are cooler than normal. Those three years — from 2020 through 2022 —could have masked the warming, they say.
There were other ocean phenomena that contributed to the warmth.
The North Atlantic experienced a marine heat wave, which is a prolonged warmth in a specific area of the ocean. That’s why we saw hot tub-like temperatures off the coast of Florida.
And the North Atlantic wasn’t the only hot spot.
This animated graphic illustrates the sea surface temperature (SST) anomaly for 2023 with the reference period of 1991-2020. In 2023, the world’s oceans were the warmest they’ve been on record. (C3S)”There are marine heat waves in basins all over: in the Atlantic, both north and south; [the] Indian Ocean, Pacific Ocean,” said Josh Willis, a climate scientist with NASA’s Jet Propulsion Laboratory. “There are these surface temperature areas that are just unusually warm. And some of that has also added to [last] year’s record.”
‘The genie doesn’t go back in the bottle’All of this — El Niño, the record-breaking sea surface temperatures, the increase in ocean heat content, the marine heat waves — has far-reaching consequences.
Coral reefs are particularly sensitive to ocean temperature changes, which cause mass coral bleaching events. This is when critical algae is forced out of the reef’s living tissue, turning them from beautiful bright colours to white. The reef isn’t dead, but it is more susceptible to mortality.
Then there’s the impact on marine life, which has economic and sustainability challenges.
“The ocean ecosystem is really critical for life on Earth, including ours,” Willis said. “And it’s under enormous pressure. And it’s pressure that most of us don’t see.”
WATCH | New efforts to save Florida’s coral reefs:
Coral reefs in Florida are hurting, but this may be the way to save themCoral reefs in the Florida Keys have been decimated by disease, human activity and rising ocean temperatures. CBC’s international climate correspondent Susan Ormiston met the scientists engineering new coral in a lab and planting them in the wild to try to restore a critical ecosystem.
And there’s the most pressing issue for humans: rising sea levels.
Willis noted that it takes a long time to add heat to the ocean and a lot of heat to change its temperature. As the oceans warm, the water “literally stands taller.”
And rising sea levels can’t be reversed.
The Intergovernmental Panel on Climate Change’s recent report noted that, sea level rise is “unavoidable for centuries to millennia due to continuing deep ocean warming and ice sheet melt, and sea levels will remain elevated for thousands of years.”
“The genie doesn’t go back in the bottle. Once the sea levels have risen, the odds of us being able to make them fall again are very, very small,” said Willis.
While we may not be able to reverse it, there is one solution in order to prevent things from becoming far worse: moving away from fossil fuels.
“Everything’s absorbing more heat because we keep adding greenhouse gases to the atmosphere,” Donner said. “If we want it to stop absorbing more heat, we need to stop that.”
ABOUT THE AUTHOR
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 Nicole.Mortillaro@cbc.ca.
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