Ocean Heat Content
Because the ocean covers over 70% of the Earth's surface it absorbs the majority of the sunlight that naturally warms the Earth. Most of the additional energy trapped in the atmosphere by greenhouse gases of both natural and human origin is also taken up by the ocean. Consequentially, quantification of ocean heat content is critical to understanding the flow of energy, among ocean, land and atmospheric reservoirs, which influences both natural variability and long-term change in the Earth's climate. Climate phenomena ranging from El Niño to sea level rise are extremely sensitive to changes in in the amount and location of heat stored in the ocean.
Comparison of three independent research estimates of ocean heat content. From Levy, J. M., Ed., 2011: Global Oceans [in "State of the Climate in 2010"]. Bull. Amer. Meteor. Soc., 92 (6), S77-S108.
The heat content of the ocean is derived from knowledge of subsurface temperatures and salinities, which are measured throughout the ocean by Argo profiling floats, by expendable bathythermographs (XBTs) dropped from an extensive network of volunteer observering ships, and by instruments deployed beneath the surface on Tropical Moored Buoys and Ocean Reference Stations.
Temperature and salinity data are archived at the NOAA National Oceanic Data Center, which produces and routinely disseminates a series of ocean heat content products that are freely available to the public both in graphical form and as data files.
Improvements in methodologies for converting ocean data to ocean heat content remains a focus of numerous research groups worldwide. One such ocean heat content product that is complementary to the NODC product is produced and distributed by the Hadley Centre at the U.K. Met Office. A different methodology is employed by scientists at the NOAA Pacific Marine Environmental Laboratory. The differences among independently-derived estimates of ocean heat content serve as an indicator of uncertainty and provide clues into how to improve the methodologies for estimation of ocean heat content.