NOAA Oceanic & Atmospheric Research | Climate Portal | Climate Program Office | Climate Observation Division

Why We Observe the Ocean

Ocean Heat Content and Transport

• Measuring changes in the amount of heat stored in the ocean is important to better understand how heat trapped by greenhouse gases is partitioned between the atmosphere and the ocean, to identify where heat enters the ocean and where it re-emerges to interact with the atmosphere, and to identify changes in thermohaline circulation and monitor for indications of possible abrupt climate change.

• Heat absorbed by the ocean raises ocean temperatures, in particular SSTs.

• The ocean is by far the Earth’s greatest reservoir for heat that accumulates as a result of the planetary energy imbalance caused by greenhouse warming. The large thermal inertia of the ocean delays the impacts of greenhouse warming, which, on the one hand presents society with an opportunity to mitigate climate change, and on the other hand commits the Earth to ongoing warming for decades to come.

• Quantifying heat sequestration via measurement of ocean temperature is, therefore, critical to predicting global temperature rise attributable to greenhouse gas emissions, and, therefore, the magnitude of emissions reductions necessary to stabilize climate.

• Increased storage of heat leads to thermal expansion of water and to local increases in air temperatures that may accelerate the melting of land-based ice, causing an increase in sea level with profound impacts on coastal communities and ecosystems.

• The ocean absorbs and stores heat at the surface and releases it to the atmosphere in remote locations, thereby contributing substantially to climate variability. The winddriven large-scale circulation of the upper layers of the ocean moves heat, salt and freshwater around the globe, thereby influencing SSTs, weather patterns, regional climate phenomena, and local sea level elevations; transport of heat between the eastern and western tropical Pacific Ocean, for example, is a critical feature of El Niño and La Niña, which profoundly impact temperature and precipitation patterns in equatorial regions. At high latitudes, cooling of salty surface waters causes them to sink to great depths where they form massive subsurface currents; the meridional overturning circulation, commonly referred to as the ocean conveyor belt, redistributes large quantities of heat in patterns that, for example, make Europe habitable.

• Tropical cyclones derive energy from the ocean, and their intensification is related to the heat content of the upper layers of the ocean directly beneath the storm tracks.