Nature and Biodiversity

Ocean warming is at a record high – what does that mean?

Ocean warming can cause polar ice sheets to melt and lead to rising sea levels.

Ocean warming can cause polar ice sheets to melt and lead to rising sea levels. Image: Unsplash/rondu

Andrea Willige
Senior Writer, Forum Agenda
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Ocean

This article is part of: Centre for Nature and Climate

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  • Sea surface temperatures are rising, with record highs reached in April 2023, according to latest data.
  • Climate scientists have described ocean warming as “heading off the charts”.
  • Ocean warming can increase storms, melt ice sheets and increase sea levels, affecting marine flora and fauna.
  • Sustained CO2 and greenhouse gas reduction are vital for reining in ocean warming, say experts.

Sea surface temperatures have hit a record high, leading to marine heatwaves around the globe, the Guardian reports. This is according to data compiled by the National Oceanographic and Atmospheric Administration (NOAA) in the US.

In early April, scientists at NOAA observed surface water temperatures of 21.1ºC, a tenth more than the highest previously recorded temperature of 21ºC in 2016. This rapid acceleration in ocean temperature “is an anomaly that scientists have yet to explain,” says the Guardian.

We may now be entering an El Niño period, when ocean warming and global temperatures increase.
We may now be entering an El Niño period, when ocean warming and global temperatures increase. Image: ClimateReanalyser

Moderate to strong marine heatwaves have been observed in areas around the globe, including the southern Indian Ocean, the south Atlantic, off the north-west coast of Africa, New Zealand, north-east of Australia and to the west of Central America.

Temperatures in our seas have been rising at least since the 1980s, but have likely been kept in check in recent years by the impact of “La Niña”. This weather phenomenon leads to cooling sea temperatures in the central and eastern tropical Pacific, which affects global temperatures.

We may now be entering an El Niño period, when ocean warming and global temperatures increase. The trajectory for ocean surface temperatures has been described by climate scientists as “headed off the charts” and a “signal that more clearly reveals the footprint of our increased interference with the climate system,” according to the Guardian.

Marine heatwaves have been observed around the world.
Marine heatwaves have been observed around the world. Image: NOAA

Ocean warming threatens the world’s largest carbon sink

The ocean is known to generate half of the oxygen we need. It absorbs a quarter of all CO2 emissions and 90% of the excess heat these emissions produce, making the ocean the world’s largest carbon sink.

Ocean warming can increase the strength of storms, cause polar ice sheets to melt and lead to rising sea levels, not to mention the impact of marine heatwaves on marine flora and fauna, including coral reefs.

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Evidence of climate change impact on the ocean ecosystem structure and marine species is among the strongest, according to the World Economic Forum’s Global Risks Report 2023.

Figure showing the impacts of climate change on marine ecosystems.
The impact of climate change on the marine ecosystem is well documented. Image: World Economic Forum
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What's the World Economic Forum doing about the ocean?

Reining in rising sea surface temperatures

As the Intergovernmental Panel on Climate Change (IPCC) recently pointed out, ocean warming has already adversely affected food production from fisheries and shellfish aquaculture in some areas. This may in turn impact on food security and livelihoods.

The IPCC acknowledges that some climatic changes – like rising sea levels – are already unavoidable and may even be irreversible. It has also stressed the vital importance of not allowing these to escalate and the need for a “deep, rapid and sustained global greenhouse gas emissions reduction”.

Escalation could lead to cascading climate events, scientists warn, in which "ice sheets and ocean currents at risk of climate tipping points can destabilize each other as the world heats up, leading to a domino effect with severe consequences for humanity," the Guardian reports.

The Forum’s Ocean Action Agenda aims to protect the ocean and the benefits it provides to people and nature, including mitigating the impacts of climate change. The community Friends of Ocean Action plays a central role in convening leaders from government, industry and civil society, who are all needed to advance solutions and positive change at the necessary speed and scale.

"We need to build ocean resilience to improve the health of marine ecosystems and their ability to withstand and recover from ocean warming and other climate change impacts, but this is not possible without reducing greenhouse gases," says Kristian Teleki, Director of the Ocean Action Agenda and Friends of Ocean Action. "The health of our ocean is inextricably intertwined with the health of our planet and we need to tackle the climate crisis and promote ocean health in unison, recognizing that we can’t achieve one without the other."

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