National Geographic: Year by year, millimeter by millimeter, the seas are rising. Fed by melting glaciers and ice sheets, and swollen by thermal expansion of water as the planet warms, the world's oceans now on average are about eight inches higher than a century ago. And this sea change is only getting started. The question is: How much higher will they go? NASA scientists are now warning that recent projections seem too conservative: Since 1992, sea levels have increased by an average of 3 inches around the world....