Ocean temperature rise accelerating as greenhouse gas levels keep rising

Record breaking ocean temperatures in 2023 and 2024 may become the new normal in the coming decades.

For 450 days between April 2023 and July 2024, average sea surface temperatures were higher than anything seen before. By analysing decades-worth of climate data, researchers at the University of Reading believe they now know how the ocean got so hot.

Their study, published in the journal Environmental Research Letters, lays the blame on ever-rising levels of greenhouse gases. Global emissions are set to reach new highs in 2025 as fossil fuels continue to be burned causing carbon dioxide levels to rise to twice what they were over 200 years ago.

Professor Chris Merchant, the lead author of the research, has reiterated calls for the world’s nations and industries to slash their emissions drastically in the coming years.

“If the oceans were a bathtub of water, then in the 1980s, the hot tap was running slowly, warming up the water by just a fraction of a degree each decade,” Chris says. “But now, the hot tap is running much faster and the warming has picked up speed.”

“The way to slow down that warming is to start closing off the hot tap, by cutting global carbon emissions and moving towards net-zero.”

How hot was 2024?

In 2024, Earth’s climate reached temperatures not seen in thousands of years. The UK’s Met Office estimates that the planet was 1.53°C warmer than it was at the end of the nineteenth century.

Not only does this make 2024 the warmest year on record, it also becomes the first calendar year to have broken through the symbolic 1.5°C figure that countries agreed to limit climate change to.

Though this pledge hasn’t technically been broken as it is measured over longer time periods than a year, we’re getting ever closer to breaching it. It’s currently believed that global warming has reached around 1.3°C, with natural climate and solar fluctuations responsible for temporarily pushing the planet over the 1.5°C threshold.

However, it’s now increasingly becoming a question of when, not if, Earth will permanently breach this limit. Research from the Met Office suggests that rising levels of carbon dioxide are now beyond the point that pathways to 1.5°C anticipated, making it even more important to limit any overshoot.

Professor Rowan Sutton is the director of the Met Office’s Hadley Centre, and was not involved in the Environmental Research Letters study.

“By itself, 1.5°C does not represent a cliff edge in terms of climate impacts,” Rowan says. “But every fraction of a degree rise in global temperature increases the frequency and severity of extreme weather events.”

“It commits the world to greater rises in sea level and increases the risk of crossing potential planet-altering tipping points such as breakdown of the Amazon rainforest biome or ice sheet collapse in Greenland or the Antarctic.”

A hotter ocean

As the Earth absorbs more energy from the Sun and reflects less back into space, much of the excess heat is being funnelled into the oceans. This has caused the rise in sea surface temperature to jump from 0.06°C per decade in the 1980s to 0.27°C per decade now.

These rising temperatures are associated with a variety of impacts, from coral bleaching to more powerful storms. Some of the hottest temperature records are associated with a climate phenomenon known as El Niño. This is a periodic weather event that causes the Pacific Ocean to grow warmer.

To see what impact this event might be having on global temperatures, the researchers compared the 2023-2024 El Niño with records from 2015-2016. They found that almost half the difference in temperature between the two events could only be explained by the oceans warming up at an accelerating rate.

As the ocean heats up even faster, the researchers anticipate that the total amount of warming seen over the past 40 years might be exceeded in less than 20. Only drastic emissions cuts will be able to bring this runaway temperature rise under control.

Many of these changes will need to be made by governments and industries, with billions of pounds needed to transform our energy networks and other infrastructure. While this might seem costly, it’s very much worth their while - in the long run, some estimates suggest it could save trillions of pounds by avoiding catastrophic climatic disasters.

Smaller changes can be made closer to home. It’s estimated that keeping livestock for meat and dairy produces almost 15% of all greenhouse emissions, so even cutting meat consumption by a small amount can go a long way to tackling climate change.

Eating more locally- or home-grown produce can also cut down on emissions from transport, as can using more sustainable forms of transport. For instance, replacing a short-haul flight from London to Madrid with a train journey can slash direct emissions by around two-thirds.

By making these changes, and many others, everyone can play their part in ensuring a cleaner and healthier environment for all.