If global warming proceeds during the this century as anticipated, it is possible that the polar ice caps will melt, substantially raising sea levels around the world (flooding coastal cities like New York, etc.).  Would this shorten, lengthen or have strictly no effect on the duration of a day?  (A "day" here means from one sunrise to the next one.)

a. lengthen the say
b. shorten the day
c. have strictly no effect on the length of a day