Obama's challenge: the world's oceans face a global-warming catastrophe.

A rise in sea levels isn't the only impact global warming is having on the world's oceans. A growing body of evidence suggests that climate change is also affecting ocean currents and the chemistry of the seas, with potentially catastrophic results on the way we live. NOW ON PBS travels deep into our oceans with scientists from the Woods Hole Oceanographic Institution and help from other researchers for a first-hand look at this stunning sea change and what we can do about it.

The NOW ON PBS Web site (www.pbs.org/now ) will feature this full program for free, as well a Web-exclusive essay depicting life following an oceanic catastrophe caused by climate change.