I think the answer there is that if you are wrong and crazy to question our current understanding of nutrition, you are probably only hurting yourself and maybe your kids. If you are wrong and crazy about climate change, you are hurting everyone on the planet. And it's a very charged topic because we already have plenty of people who don't want to inconvenience themselves to benefit the climate, so questioning climate change tends to give such people more justification for behavior that is selfish to the point of monstrous already.

I'm an environmental studies major. I think it's complicated. I tend to not bother to argue it. My doubts are not some kind of definitive proof that the assertions of others are wrong. I mostly think it's not worth debating at this point in time.

There are plenty of negative changes that are well documented, such as species going extinct, species on the Endangered Species list, etc. We don't really need to prove global warming one way or the other to know that we need to make some changes in a big way and very soon because the course we are on is clearly a crash course.