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The average surface temperature and that of the upper 2,000 metres of the world’s oceans were the highest in 2024, a new analysis showed.
The ocean heat content for the upper 2,000 m of global oceans saw a significant increase — 16 (± 8) Zetta Joules (ZJ) compared to 2023, according to the report published in Advances in Atmospheric Sciences.
The global annual mean sea surface temperature in 2024 was 0.61°C above the 1981-2010 baseline, slightly exceeding the 2023 record, it added. Despite a slight decline in the second half of the year, the annual mean temperature still set a new record.
The record-high SSTs and ocean heat content (OHC) in 2024 contributed to higher atmospheric water vapour levels. The rate of evaporation rises with higher sea surface temperatures. Warmer water transfers more heat to the atmosphere, causing more water to evaporate into the air. This process boosts the overall moisture content in the atmosphere.
“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,” said Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research, United States, a member of the team did the analysis.
The increased water vapour acts as a feedback mechanism by trapping more heat in the atmosphere, further warming the planet. Ocean warming contributes significantly to global sea level rise through thermal expansion.
Moreover, the higher atmospheric moisture content fuelled by ocean warming has led to more extreme weather events in 2024, such as intense rainfall, storms and hurricanes. The heavy rainstorms in South China during the summer of 2024 and the intense Hurricane Helene in the United States that caused devastating floods were fed my the additional moisuture pumped from the warming oceans.
Six of the eight ocean regions, including the Indian Ocean, tropical Atlantic, Mediterranean Sea, North Atlantic, North Pacific and Southern Ocean, showed record-high OHC values in 2024, the authors of the report noted.
The Indian Ocean saw a sharp increase in OHC, rising by 10.3 Zetta Joules (ZJ) compared to 2023, mainly caused by the global El Nino event that last till the middle of the year and was one of the five most powerful El Nino Southern Oscillation event in history.
The warming of the Indian Ocean is connected to regional climate phenomena, such as intensified monsoons and shifts in precipitation patterns, which likely influenced weather conditions in India during 2024.
The Mediterranean Sea is the region showing the "most intensive warming rate", the researchers noted in the report. It experienced an area- averaged OHC increase of 1.1 ZJ compared to 2023, surpassing all other regions. The warming rate in the Mediterranean was about five times higher than the mean rate over the past two decades, they added. This significant change has profound implications for marine biodiversity and regional climate patterns.
The North Pacific showed a 3.8 ZJ rise compared to 2023, representing a continuation of its long-term warming trend, which has been evident since the 1990s, significantly impacting intermediate water masses and contributing to marine heatwaves.