. >> reporter: economist marty weitzman thinks his property on a marsh in gloucester, massachusetts,ere. >> reporter: right. >> and what's happened is that it's caused erosion at the edge of the lawn. >> reporter: well, but a couple of inches doesn't seem like much. >> maybe that wouldn't be, but it's really a couple of feet that we're headed for. >> reporter: a couple of feet, or conceivably, several dozen, says gernot wagner, a former student of weitzman's who's now at the environmental defense fund. last time concentrations of co2 were as high as they are today, we did in fact have sea levels up to 66 feet higher than today. well, 66 feet and this house is gone. >> reporter: now, weitzman and wagner can't know for sure, of course, that manmade higher temperatures are rising the tides here or anywhere else. but a plausible probability of true catastrophe was enough to prompt "climate shock," about the dangers that lurk, dangers weitzman wasn't worried about when he first went into environmental economics years ago. >> i was wondering, how could it be possible that mere human beings