>> i think we've got it. >> okay. >> let me ask you about this. you know, my sense is that climate change and evolution are like gravity. they're a fact. drop a quarter, it falls. it's a fact. don't argue about it. it's not one of the many theories out there. it is a scientific reality. if somebody has some other standard besides science, i want to hear what it is, business practices, religion, tell me you have some other way of judging something besides the scientific method. as a scientist, is there any doubt that climate changing is a problem and it's caused by man? >> well, there are a few things in science that we're ascertain about as the fact that we are warming the planet by increasing greenhouse gas concentrations through fossil fuel burning and other human activities. maybe gravity, maybe there are a few other propositions in science that we have as high a level of certainty about as we have about this issue of human-caused climate change.