Ninety percent of global warming is occurring in the ocean, causing the water’s internal heat to increase since modern recordkeeping began in 1955, as shown in the chart. (The shaded blue region indicates the 95% margin of uncertainty.)
Each data point in the chart represents a five-year average. For example, the 2018 value represents the average change in ocean heat content (since 1955) for the years 2016 to and including 2021.
Heat stored in the ocean causes its water to expand, which is responsible for one-third to one-half of global sea level rise. Most of the added energy is stored at the surface, at a depth of zero to 700 meters. The last 10 years were the ocean’s warmest decade since at least the 1800s. The year 2021 was the ocean’s warmest recorded year and saw the highest global sea level.