Rising Sea Levels is rapid rise in sea level that has been seen in the past century. Sea levels have risen an estimated 6 inches since 1920 (0.06 inches per year). Global warming proponents point to the nearly 0.11 inch average rise over the past 20 years as a sign that levels could rise up to 3 feet in the next hundred years. That could mean that Bangkok could be underwater by 2030. Conservative estimates give the city about 100 years before the streets are constantly covered by water.