The 
Greenland and 
West Antarctic ice caps are melting, but at only half  
the rate previously predicted, according to a team of U.S. and Dutch  
researchers.    
Past estimates of the rate of ice-cap melting in Greenland and western  
Antarctica may not have properly accounted for movements in the Earth's  
crust that alter mass distribution and influence the gravitational  
field.    
Using data from satellites and GPS measurements of land and sea-floor  
pressure, the researchers concluded that the ice caps are melting at  
approximately half the speed originally predicted and, as a  
consequence, that the average rise in sea levels will also be less.  
However, they cautioned that "there are too few data available to  
verify this independently."