Another Record: Ocean Warming Continues through 2021 despite La Nina Conditions

The increased concentration of greenhouse gases in the atmosphere from human activities traps heat within the climate system and increases ocean heat content (OHC). Here, we provide the first analysis of recent OHC changes through 2021 from two international groups. The world ocean, in 2021, was the hottest ever recorded by humans, and the 2021 annual OHC value is even higher than last year's record value by 14 +/- 11 ZJ (1 zetta J = 10(21) J) using the IAP/CAS dataset and by 16 +/- 10 ZJ using NCEI/NOAA dataset. The long-term ocean warming is larger in the Atlantic and Southern Oceans than in other regions and is mainly attributed, via climate model simulations, to an increase in anthropogenic greenhouse gas concentrations. The year-to-year variation of OHC is primarily tied to the El Nino-Southern Oscillation (ENSO). In the seven maritime domains of the Indian, Tropical Atlantic, North Atlantic, Northwest Pacific, North Pacific, Southern oceans, and the Mediterranean Sea, robust warming is observed but with distinct inter-annual to decadal variability. Four out of seven domains showed record-high heat content in 2021. The anomalous global and regional ocean warming established in this study should be incorporated into climate risk assessments, adaptation, and mitigation.

Automated summary

The increased concentration of greenhouse gases in the atmosphere leads to a rise in ocean heat content and the warming of the world ocean. In 2021, the ocean reached its highest temperature on record, with an annual ocean heat content value surpassing the previous record by approximately 14 to 16 zetta joules. Long-term ocean warming is more prominent in the Atlantic and Southern Oceans and is primarily attributed to the increasing concentration of anthropogenic greenhouse gases. The year-to-year variation in ocean heat content is mainly influenced by the El Nino-Southern Oscillation. Significant warming is observed in the Indian, Tropical Atlantic, North Atlantic, Northwest Pacific, North Pacific, Southern Oceans, and Mediterranean Sea, with four out of seven regions showing record-high heat content in 2021. The anomalous global and regional ocean warming identified in this study should be considered in climate risk assessments, adaptation, and mitigation efforts.