we can stop some of these changes that are happening in the arctic, but that does meanan we're goioing o have to cocommit to reducing the amount of fossil fuels we're putttting in t the atmososphered that's the real challenge. >> most experts say fossil f fus are the leading cause of climate change. the climate change deniers often associated with the fossil fuel lobby and industry-supported think tanks downplay the connection between fossilil fuels and the warming f our planet. climate scientist michael mann on how a changing climate may affect our future. >> sometimes you''ll hear from the e itics. thehey'll say, "we demand proof that humanans are causing thihis." and my response is that t proof is reserved for alcoholic beverages andd mathematitical theorems."tt doesn't characterize how scienee works. science works thrhrough weights of evidence, through likelihoods, through confidence levels, and so we're about as certain that humans are causing global warming as we are about any scientific proposition, but we never say we've provenen someththing in science because there's always th

i meanan, we've seen, youou kno, one of the biggest oututcries in protest in decades, and historical amounts of protest, in dakota access. and for him to -- fofor him to y that there was that it was met with no response is a total lie. that's one of his -- another alternative facts that he has, when the reality is, you know, tens of thousands of people sacrificed. we sacrificed our freedoms to protect this water. we sacrificed everything that we had. and it was women and children and families, and indigenous people with our allies from all over the country and all over the world. people around the world understand what happened at standing rock. and i think this is a constant sort of pr thing that says, "oh, nobody cares." but the reality is, people do care and that, now, you know, there's an established movement in this country. there's an established indigenous rights movementnt. it's starting to converge with these other movements. and he's not going to be able to say -- you know, he's going to be able to say those things all he wants, but there's a growing movement across this co