'How do they know all this climate stuff?'

Moon rises over Thunder Bay as seen from Nolalu, ON

If you don't understand all the information coming at you about climate change, I highly recommend Earth's Changing Climate, a course taught by Professor Richard Wolfson as part of the Great Courses program.

The Great Courses are university-level courses that you purchase to be viewed on your computer or listened to in your car. I prefer listening to these courses instead of commercial radio. Lectures are 30-45 minutes in length and there are usually 18 or so lectures to a course.
Courses like Earth's Changing Climate are designed for non-scientists so don't be afraid that you won't be able to understand. At the same time Earth's Changing Climate gives you all the facts and tells you what is known and not known about climatic processes.
Climate change is going to drastically affect us all. The more you know, the more prepared you will be.