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Ocean Heat Content

How much heat the ocean has absorbed as the planet warms.

Ocean heat content since 1992

Full ocean depth, monthly, seasonal cycle removed. Credit: ECCO, NASA JPL
Change since 1992
…ZJ
Average rate
…ZJ/yr
Rate since 2015
…ZJ/yr
MonthlyLinear trend
Heat content of the whole ocean, surface to sea floor, relative to the 1992 average. One zettajoule (ZJ) is a billion trillion joules.

Where the heat is going

Heat gained since 1992 above each depth. Credit: ECCO, NASA JPL
Each line is the heat stored between the surface and that depth. Thin lines are monthly values and thick lines a 13 month running mean. Percentages are each layer's share of the full depth total. .

An independent check from ocean measurements

Upper 2000 m, three month averages. Credit: NOAA NCEI
Latest
…ZJ
Rate
…ZJ/yr
Three month averageUncertaintyLinear trend
Measured directly by Argo floats and other instruments, relative to the 1955 to 2006 average, and updated every three months, so it runs later than ECCO.

Key takeaways

  • The ocean has gained about … zettajoules of heat since 1992, from the surface to the sea floor.
  • The rate has grown. Since 2015 the ocean has gained about … zettajoules a year, compared with about … on average since 1992.
  • That heat makes seawater expand, which accounts for roughly 40 percent of today's sea level rise.

What is ocean heat content?

Ocean heat content is the total amount of heat stored in the ocean. Because water holds far more heat than air, the ocean is where about 90 percent of the extra energy from global warming ends up. Ocean heat content is one of the most reliable measures of how fast the planet is warming, because it is not affected by the short swings in weather that make surface temperatures noisy.

What are we looking at?

The main chart comes from ECCO, NASA's Estimating the Circulation and Climate of the Ocean project. ECCO combines nearly all available ocean observations, from satellites measuring sea level, gravity and sea surface temperature to Argo floats and ship surveys, with a physical model of the ocean. The result is a complete, physically consistent estimate of the ocean every month, including the deep ocean below 2000 m that instruments rarely reach. That is why ECCO can track heat all the way to the sea floor.

The second chart splits that heat by depth. Most of it is still near the surface, but a growing share is reaching deeper layers. The third chart is an independent check: NOAA's estimate of the upper 2000 m built directly from ocean measurements. For the upper 2000 m since 2005 the two give similar rates of warming, within about 10 percent of each other.

Why do we care?

Warmer water takes up more space, so ocean heat content and steric height rise together. Ocean warming also fuels stronger storms, bleaches coral reefs, and melts the floating ice shelves that hold back Antarctic glaciers, which adds to sea level rise from Antarctica.

Data: ECCO, NASA Jet Propulsion Laboratory, global ocean heat content (ecco-group.org). The most recent year is a preliminary extension of the ECCO solution. The seasonal cycle is removed on this site by least squares. NOAA National Centers for Environmental Information, global ocean heat content 0 to 2000 m (ncei.noaa.gov).