Rising sea levels could put millions at risk by 2030

>>> warmer weather can have a dark side . tonight there is a new projection that rising seas due to climate change could cause a whole lot of damage much sooner than anyone had previously thought. the report from our chief environmental affairs correspondent anne thompson .

>> that is one angry click.

>> reporter: the ferocious surge the atlantic powered by hurricane irene last august moved a lifeguard tower. broke through a sea wall and sent water rushing into the streets of new york 's long beach. a scene that will become more commonplace, a new study says, because of rising sea levels caused by global warming . been man straws says the odds of a 100-year flood happening by 2030 doubles for 2/3 of the places studied.

>> we found that once a 100-year flood becomes a once a decade-year flood fastest in southern california where we expect to see that in several decades.

>> reporter: by 2030 the 5 million americans living on coastal land less than four feet above high tide lines. by 2050 it expands to 6 million people living less than five feet above high tide lines. in new york city , the danger is not just to the low-lying areas where millions live but to the very way people get around. the funnel-shaped new york harbor could flood the city's vital subway system . loading the dies, heat-trapping gasses from burning oil, gas, warming the ocean. measurements taken in bermuda show 58 years of increases.

>> the temperature will be in red, there is more heat in a couple of meters of the ocean than the atmosphere.

>> reporter: septics say you can't blame the rising ocean all on global warming .

>> the sea level rise caused by climate change is less than the sea level rise caused from land sinking, and we can't stop it.

>> reporter: a future dependent on the ocean and threatened by it. anne thompson , nbc news, new