Ocean Warming

OCEAN HEAT CONTENT CHANGES SINCE 1955 (NOAA)

Data source: Observations from various ocean measurement devices, including conductivity-temperature-depth instruments (CTDs), Argo profiling floats, and eXpendable BathyThermographs (XBTs). Credit: NOAA/NCEI World Ocean Database

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.

Fire coral bleaching Coral bleaching is a consequence of a warming ocean. This image shows bleached coral off Islamorada, Florida. Credit: Kelsey Roberts/USGS

Covering more than 70% of Earth’s surface, our global ocean has a very high heat capacity. It has absorbed 90% of the warming that has occurred in recent decades due to increasing greenhouse gases, and the top few meters of the ocean store as much heat as Earth's entire atmosphere.

The effects of ocean warming include sea level rise due to thermal expansion, coral bleaching, accelerated melting of Earth’s major ice sheets, intensified hurricanes, and changes in ocean health and biochemistry.