The 2023 study by the Institute of Atmospheric Physics (IAP),
CAS reveals a record high in ocean heat absorption, attributed
to increased greenhouse gases. Involving 34 scientists globally,
it highlights oceans as reliable climate change indicators,
with data showing a significant 2023 heat increase. The study
warns of the impacts on marine life and weather patterns,
emphasizing the urgency of reducing greenhouse gas emissions.
The world’s oceans absorbed more heat in 2023 than in any other year
since records began, according to a paper released today
(Cheng, L. J. et al. Adv. Atmos. Sci. https://doi.org/10.1007/s00376-024-3378-5 (2024).).
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 5 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 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.
The 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. 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.
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 as “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 at 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.”
Provided by the IKCEST Disaster Risk Reduction Knowledge Service System