Abrupt Climate Change

Testimony to the Senate Committee on Commerce, Science and Transportation

William Curry
Ocean and Climate Change Institute Director
Woods Hole Oceanographic Institution
May 6, 2002

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Recent Changes in the Ocean

The ocean contains 97% of the water on the planet and plays a large role in the earth's hydrological cycle, which is the movement of water on Earth. In the warm tropical regions, water is evaporated from the oceans, leaving behind and concentrating the salts dissolved in the seawater. The water vapor is transported by the atmosphere toward higher latitudes, where it falls as rain and snow, adding freshwater back into the oceans and diluting salt concentrations at higher latitudes. As a result, the salinity of seawater is higher in the tropics and lower at higher latitudes. This is noticeable if you have ever experienced the saltiness of Caribbean waters compared to those in Ocean City, Maryland, or Cape Cod. Movement (circulation) of salty ocean water from high to low latitudes balances the movements of the water in the atmosphere, off setting some of the salinity diff erences between high and low latitudes.

During the last four decades, oceanographers have observed large changes in the distribution of salinity, which appear to be related to the gradual warming of the atmosphere (see Figure 1). In the tropical regions of the Atlantic, Mediterranean, Indian, and Pacific Oceans, surface waters have increased in salinity, reflecting an increasing rate of evaporation in those locations caused by warmer ocean and air temperatures. At the same time, salinities have been decreasing in the subpolar and polar regions of both hemispheres: The high-latitude ocean is gaining freshwater because of higher precipitation, increased runoff from rivers, and increased melting of glacier ice and sea ice. These salinity changes are unprecedented in the relatively short history of the science of oceanography. Click here for full story...

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