OCEAN HEAT CONTENT CHANGES SINCE 1955 (NOAA)
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, expressed in zettajoules. For example, the 2021 value represents the average change in ocean heat content (since 1955) for the years 2019 up to and including 2023.
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 2023 was the ocean’s warmest recorded year.