When it comes to climate change, we should be paying more attention to our oceans

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. 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."