The heat stored in the world’s oceans increased by the greatest margin ever in 2023

Oceans break heat records five years in a row

The heat stored in the world’s oceans increased by the greatest margin ever in 2023

The world’s oceans absorbed more heat in 2023 than in any other year since records began, according to a paper released today¹ (see 'Hotter and hotter').

The findings are the latest update of an annual study led by the Institute of Atmospheric Physics (IAP) at the Chinese Academy of Sciences in Beijing. The researchers say that the oceans have been warming at record-breaking rates every year since 2019. A total of 34 scientists from 19 research organizations in five countries participated in the research.

Cheng Lijing, an oceanographer at the IAP and the lead author of the paper says that the findings reflect the growing amount of human-generated greenhouse gases in the atmosphere. “The oceans store 90% of the excess heat in the Earth’s system. As long as the level of greenhouse gases remains relatively high in the atmosphere, the oceans will keep absorbing energy, leading to the increase of the heat in the oceans.”

He calls ocean heat content a “particularly robust indicator” of global climate change because it is much less affected by natural fluctuations in the Earth’s system than are air temperatures and sea surface temperatures.

Cheng and his co-authors studied two data sets on ocean heat content: one from the IAP and the other from the National Centers for Environmental Information (NCEI) at the National Oceanic and Atmospheric Administration of the United States.

The IAP data show that the heat stored in the upper 2,000 metres of oceans increased by 15 zettajoules in 2023 compared with that stored in 2022. This is an enormous amount of energy — for comparison, the world's total energy consumption in 2022 was roughly 0.6 zettajoules.

NCEI’s figure for the 2023 increase is 9 zettajoules. The discrepancy between the two figures is caused by the different calculation and data quality-control methods used by the organizations (see 'Different but the same'). But “the important point in the paper and for scientific understanding is that the ocean is warming consistently, year over year to new record levels of ocean heat content”, says Tim Boyer, an oceanographer with the NCEI and one of the paper’s co-authors.

Sea levels and life

Svetlana Jevrejeva, a sea-level scientist with the National Oceanography Centre in Liverpool, UK, says that the study provides “robust observational evidence” that the oceans were the warmest on record in 2023. She regards it “very alarming” that the ocean-heating record has been broken five years in a row.

Even small changes in the oceans can yield far-reaching impacts, she says. For example, about 50% of current sea-level rise is attributed to the expansion of the oceans when waters get warmer. Rapid ocean warming could lead to intensification of extreme weather events, she notes, because oceans mediate global weather patterns that determine rainfall, droughts and floods.

William Cheung, a marine ecologist at the University of British Columbia in Vancouver, Canada, says that ocean warming could lead to shifts in the distribution of marine life, causing some species to move towards polar regions or deeper waters.

A warmer ocean could also trigger changes in the timing of biological events, such as migration and reproductive cycles, and affect the body size of marine creatures, says Cheung.

Christina Hulbe, a glaciologist from the University of Otago in Dunedin, New Zealand, says that as long as the concentration of greenhouse gases in the atmosphere keeps going up, the atmosphere and the ocean will keep warming. But the “flip side” is that as soon as we “get our act together” to reduce emissions enough to enable a decline of greenhouse-gas concentration, the warming trend will change.

She warns that the more greenhouse gases humans produce, the more likely it is that some tipping points will be triggered.

“We don’t know if those thresholds have been crossed yet,” she says, “and it is urgently important to stop warming before they are.”

doi: https://doi.org/10.1038/d41586-024-00081-0

This story originally appeared on: Nature - Author:Xiaoying You