I think most people realize the world is in a warming period, as far as the history of the planet earth goes. Nobody disputes this that I have ever seen.
I also think most people realize that things like car, factory, airplane exhaust pollutes our air and water; and also that man has directly killed off species (for example, we shot all the millions of passenger pigeons in the world, there are none left, gone forever) The Colorado River no longer runs to the sea.
It's obvious that man can permanently change his environment. We've already done it.
This has mainly only occurred in the last couple hundred years of the earth's history, as the industrial revolution and the worlds population of humans has exploded exponentially.
Life on earth (man's involvement) was very different 300 years ago than it is now.
The hard part for some is taking the knowledge that we can pollute and change our environment and kill off species, and expanding that to believe that our actions can permanently change, not only our local environments, but the environment of the entire planet. That is a big concept to wrap around.
All I can say is read up on it, see pictures of it. Even if you read it or watch it with a grain of salt, see what "is".
http://environment.nationalgeographi...lobal-warming/