JUDY WOODRUFF:

A closer look now at the specifics, and the questions raised by this from two people who worked on the report. Michael Oppenheimer is a coordinating lead author of it and a professor of geosciences and international affairs at Princeton University. And Patricia Romero Lankao of the U.S. National Center for Atmospheric Research, she was a lead author of a chapter about North America. She's a sociologist who studies the societal impact of climate change.

And we welcome you both to the program.

Michael Oppenheimer, it seems one of the screaming headlines from this is that people need to pay attention. What had been felt to be in the future is happening now. How do you read the main conclusions today?

MICHAEL OPPENHEIMER, Professor of Geosciences and International Affairs, Princeton University: Right.

We're already detecting some of the effects of climate change on the whole system we live in. We're detecting changes in crop yields. We're detecting changes in the frequency of heat waves, and heat waves kill, and we're detecting the massive changes in globally important systems like the arctic or coral reefs, on which people's lives depend and which the whole climate system depends.

So changes are happening and we need to get on doing something about it, both reducing the emissions that are causing the problem and learning to adapt, because some of the climate change is inevitable.