The ocean surrounding the Antarctic continent is experiencing one of the fastest warming rates. (Credit:
Chao Ban)
BEIJING — In 2024, much of the world focused on rising air temperatures, but something similar was boiling beneath the waves. Scientists from across the globe tracking ocean temperatures discovered new records being set not just at the surface, but thousands of meters below, signaling a fundamental shift in Earth’s climate system.
“The broken records in the ocean have become a broken record,” says lead author Lijing Cheng with the Institute of Atmospheric Physics at the Chinese Academy of Sciences, in a statement.
Ocean temperatures surged to unprecedented levels last year, breaking away from previous records set in 2023, according to the research published in Advances in Atmospheric Sciences. The analysis, conducted by 54 scientists from seven countries, paints a sobering picture of accelerating ocean warming that outpaces previous projections.
Cheng et al.)
Scientists measure ocean heat content (OHC) in zettajoules, a mind-boggling unit where one zettajoule equals one sextillion joules of energy. In 2024, the upper 2,000 meters of the world’s oceans absorbed an additional 16 ± 8 zettajoules of heat compared to 2023 levels, which is equivalent to roughly 140 times the world’s total electricity generation in 2023.
“OHC has increased steadily by 15-20 ZJ over the past five years despite the La Niña and El Niño cycles,” notes Michael Mann from the University of Pennsylvania.
Most concerning to researchers was the observation that warming rates have increased two to threefold since the late 1980s. While the ocean gained heat at a rate of about 2.9 zettajoules per year from 1958-1985, that rate has jumped to approximately 9 zettajoules per year since 1986. This acceleration of ocean warming parallels rising greenhouse gas concentrations in the atmosphere, with CO2 levels exceeding 420 ppm in 2024, which is the highest level in at least 2 million years.
What Are El Niño and La Niña?
El Niño and La Niña are phases of the El Niño–Southern Oscillation (ENSO), a natural climate cycle in the Pacific Ocean that influences global weather. El Niño occurs when trade winds weaken, causing warm water to pool near the Americas, leading to wetter conditions in places like South America and the southern U.S., and droughts in regions like Australia and Southeast Asia. In contrast, La Niña strengthens trade winds, pushing warm water toward Asia and allowing cooler water to rise near the Americas, resulting in wetter winters in the Pacific Northwest and drier conditions in the southern U.S. These cycles shape rainfall, temperatures, and storms worldwide, impacting ecosystems, agriculture, and economies.
“To know what is happening to the climate, the answer is in the ocean,” says co-author John Abraham at the University of St. Thomas. The ocean is particularly crucial as it stores about 90% of excess heat from global warming and covers 70% of Earth’s surface, effectively dictating weather patterns through heat and moisture transfer into the atmosphere.
Surface waters showed particularly dramatic changes. Global sea surface temperatures in 2024 averaged 0.61°C above the 1981-2010 baseline, slightly higher than 2023’s already record-breaking temperatures. Six major regions experienced record-high heat content in 2024.
“The main way the ocean continues to influence the climate is through accompanying increases in water vapor in the atmosphere that leads to the damaging increases in extremes in the hydrological cycle,” explains Dr. Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research. “Water vapor is also a powerful greenhouse gas and increased heating leads to drying and risk of drought and wildfire. But it also fuels storms of all sorts and leads to risk of flooding. That includes hurricanes and typhoons.”
These impacts are already evident. Over the past 12 months, 104 countries recorded their hottest temperatures ever. Droughts, heat waves, floods, and wildfires have impacted regions across Africa, Southern Asia, the Philippines, Brazil, Europe, the U.S., Chile, and the Great Barrier Reef. Since 1980, climate disasters have cost the U.S. nearly $3 trillion.
The Mediterranean Sea showed the most intensive warming rate among all regions studied, with heat content increasing by 0.41 gigajoules per square meter (equivalent to 1.1 zettajoules total) from 2023 to 2024—approximately five times higher than the region’s average warming rate over the past two decades.
“The ocean is our sentinel for planetary warming, acting as the major sink of surplus heat accumulating in Earth’s climate system as a result of anthropogenic emissions,” says co-author Dr. Karina von Schuckmann at Mercator Ocean International.
As ocean temperatures continue their upward climb, scientists warn that these records represent more than just numbers on a chart. Without dramatic reductions in greenhouse gas emissions, each passing year will likely bring new records, new challenges, and increasingly costly impacts for communities worldwide.
Paper Summary
Methodology
The research team consisted of 54 scientists from 7 countries analyzing ocean temperature data from multiple independent sources, including direct measurements from ships, buoys, and autonomous Argo floats. Three different research groups – IAP/CAS, CIGAR-RT, and Copernicus Marine – processed and analyzed data independently, focusing on the upper 2000 meters of the ocean where most warming occurs. Scientists used the 1981-2010 period as a baseline for comparing temperature changes, allowing them to determine whether specific years were warmer or cooler than this reference period.
Results
- Ocean heat content in 2024 exceeded 2023 levels by 16 ± 8 zettajoules (IAP/CAS data), 18 ± 7 zettajoules (CIGAR-RT data), and 40 ± 31 zettajoules (Copernicus Marine data)
- The heat increase from 2023 to 2024 equals approximately 140 times the world’s total electricity generation in 2023
- Global sea surface temperatures averaged 0.61°C above the 1981-2010 baseline
- Six major ocean regions hit record-high temperatures
- OHC has increased steadily by 15-20 ZJ annually over the past five years, despite natural climate variations
- 104 countries recorded their highest-ever temperatures over the past 12 months
- Since 1980, climate-related disasters have cost the United States nearly $3 trillion
Limitations
The researchers note that real-time updates of climate datasets face additional constraints compared to historical analyses. Data quality in real-time isn’t always guaranteed. Additionally, different data processing methods between research groups led to some variations in the exact magnitude of warming, though all showed significant increases. Regional variations in warming patterns can also make it challenging to predict specific local impacts.
Discussion and Takeaways
The research demonstrates that ocean warming is accelerating despite natural climate variations like El Niño and La Niña cycles. The ocean acts as Earth’s primary heat sink, absorbing 90% of excess warming and covering 70% of the planet’s surface. This warming drives extreme weather events through increased atmospheric water vapor, leading to more severe storms, floods, droughts, and wildfires. Without significant emissions reductions, these impacts will likely intensify, bringing greater economic and environmental costs. Recent examples of impacts span multiple continents, affecting regions from the Great Barrier Reef to the Mediterranean Sea.
Funding and Disclosures
The research was supported by multiple institutions including China’s National Key R&D Program, the International Partnership Program of the Chinese Academy of Sciences, the US National Science Foundation, NASA, NOAA, and various European research organizations. The authors declared no competing interests.
Publication Information
“Record High Temperatures in the Ocean in 2024” was published in Advances in Atmospheric Sciences in January 2025. Lead author Lijing Cheng from the Institute of Atmospheric Physics, Chinese Academy of Sciences, coordinated with 53 international co-authors representing major climate research institutions worldwide.
