2100 could be much higher.co business andmics correspondent paul solman focuses on the extreme risks aseme of the worst scenarios. his story is part of our "making sense" series, and part our contribution to "covering climate now," a global llaboration of more thanab 300 news outlets to enhance coverage of the climate story. >> so look, you can start to see erosion along here... >> reporter: economist martin weitzman, four-plus years ago, on the homtead he built onhe north shore of massachusetts. >> the water has risen a couple of inches at least, in the time, in the 40 years i have been living here. >> reporter: a usually understated, math and data driven theorist, weitzma who died in the past few weeks,di began as a climate catastrophe skeptic. >> i was wondering, how could it be possible that mere human beings could change the climate in a serio way? >> reporter: but geologic samples of carbon dioxide going back millenniaidegan to scare him. >> we were way outside the historical range for at least 800,000 years, and we're climbing very strongly.he at t current trajectory that we're on,