Humans may or may not be changing the average environmental temperatures. It is not a possibility that it is changing, I guarantee it. Some people really believe that our world would be completely stable if we weren’t a part of it. Generally speaking I call these people hippies.
People tend to forget that a few millenia ago (just a blink in Earth’s eye) there was an ice age. There have been several actually. While “life” may have played a factor, so have solar flares, volcanic activity, continenetal drift and possibly many other things. The climate of Earth will change. It will be slow and there won’t be much we can do about it. Statistically speaking the Earth will outlast our species just has it has every species before it.
Hug a tree if it makes you happy, don’t polute because dirty doesn’t help. However stay off my ass and don’t lay a guilt trip on my because I drive a big (and yellow) SUV.