Since 2018, a group of international researchers has been tracking the amount of heat absorbed by the world's oceans, and in 2025, their measurements reached a new high, marking the eighth consecutive year of increasing ocean heat absorption. The study, published Friday in the journal Advances in Atmospheric Science, revealed that the world's oceans absorbed an additional 23 zettajoules of heat in 2025, the highest amount recorded since modern measurements began in the 1960s.

This figure significantly surpasses the 16 zettajoules absorbed in 2024, according to the research conducted by a team of over 50 scientists from the United States, Europe, and China. A joule, a standard unit of energy measurement, is relatively small, capable of powering a small lightbulb for a second or slightly heating a gram of water. A zettajoule, however, is one sextillion joules, meaning the 23 zettajoules absorbed by the oceans this year is equivalent to 23,000,000,000,000,000,000,000 joules.

The continuous increase in ocean heat absorption is a critical indicator of climate change. Oceans act as a massive heat sink, absorbing over 90% of the excess heat trapped by greenhouse gas emissions. This absorption mitigates some of the surface warming effects of climate change, but it also leads to significant consequences for marine ecosystems and global weather patterns.

Warmer ocean temperatures contribute to rising sea levels through thermal expansion, threaten coral reefs with bleaching events, and intensify extreme weather events such as hurricanes and cyclones. The increased heat also alters ocean currents, impacting marine life distribution and fisheries.

The research underscores the urgency of reducing greenhouse gas emissions to mitigate the impacts of climate change. Scientists emphasize that limiting global warming requires significant and sustained reductions in carbon dioxide and other greenhouse gases. The continued monitoring of ocean heat content is crucial for understanding the Earth's climate system and predicting future climate scenarios. The researchers plan to continue their annual assessments to track the ongoing changes in ocean heat absorption and provide valuable data for policymakers and the public.