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CHAPTER 2 

 THE SCIENTIFIC BASIS FOR PROJECTING SEA LEVEL RISE 



Global sea level depends primarily on three factors: 

 (1) the total amount of water tliat rests in ocean basins rather 

 than on land; (2) ocean temperatures at various depths, which 

 determine ocean density and volume; and (3) the shape (bathymetry^ 

 of the ocean floors.^/ Global warming could increase the 

 water resting in the oceans and the volume of tnat water, and 

 thereby raise sea level. Because changes in bathymetry are 

 slow and unlikely to accelerate, this report considers only 

 the first two factors. 



This chapter discusses the scientific basis for expecting 

 a global warming to occur, and the linkages between that warming 

 and sea level. 



GREENHOUSE GASES HELP DETERMINE THE PLANET'S TEMPERATURE 



The earth's temperature is determined by three factors: 

 the sunlight it receives, the sunlight it reflects, and the 

 infrared radiation absorbed by the atmosphere.^/ Without the 

 influence of the atmosphere, incoming visible radiation (in 

 the form of sunlight) and outgoing radiation (in the form of 

 invisible infrared radiation) would balance to yield a certain 

 surface temperature. However, the atmosphere contains gases 

 such as CO2 and water vapor that absorb some of the infrared 

 radiation. These gases are warmed by the radiation and radiate 

 energy back to the earth's surface, raising its temperature. 



