Earth's oceans store the vast majority of heat in the climate system. As ocean currents circulate water around the planet, some of the stored heat is released back into the atmosphere. Climate scientists monitor how much heat is released by taking the ocean's temperature. Sea surface temperature, or SST, is the temperature of the top millimeter of the ocean's surface. It is recorded daily around the world by satellite instrumentation, ocean buoys, and other sensors. Tracking SST can provide important insights into short-term weather events and be critical for developing long-term climate models.

Oceans can absorb lots of heat with little or no appreciable temperature change. This property is called heat capacity. The total heat capacity of a substance depends on its mass as well as its capacity for holding heat—which is measured by its specific heat, the amount of heat needed to raise the temperature of one gram of the substance by 1°C. The top 2 meters (6.5 feet) of ocean can store as much heat as can be contained in the entire atmosphere.

Through various processes, atmospheric heat gets mixed into the upper 90 meters of ocean—not just the top 2 meters. Mixing in the heat over a much greater volume effectively stores it for several years before its release. In this way, the oceans store more than 90 percent of the heat in Earth's climate system, and they act like a buffer to moderate the effects of climate change.

Many scientists think that accumulating greenhouse gases, including carbon dioxide, have created a dangerous heat imbalance in the atmosphere. While some of the trapped heat has been melting glacier surfaces, most has been absorbed by the oceans. This surplus heat is causing water to expand and, consequently, sea level to rise. Researchers are also analyzing whether cyclical changes in solar activity may be a contributing factor. In any case, an increase in heat content may be responsible for ocean temperature and sea level increases that were reported in 2008 as being 50 percent greater than they were just one year earlier.

As the interactive activity indicates, monitoring changes in sea surface temperature helps scientists better understand its wide-ranging impacts. Based on knowledge passed down through generations, Native peoples and others who depend on the sea for their sustenance or economic well-being are also aware of changes in the ocean. And because they observe subtleties not normally detected by satellite monitoring equipment, their pool of evidence may differ from—though still complement—that which is gathered by scientists and serve as a valuable tool in analyzing what is happening in the ocean and on land.

Because weather patterns, sea ice formation, sea level, and marine biodiversity are all factors inherently tied to ocean temperature, we can recognize the potential impact that changes might bring and the linkages they carry. For example, while polar bears and walruses move north as sea ice disappears beneath them, some coastal Alaska communities are being forced to relocate as their traditional food sources vanish.

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