I think both sides agree that the climate of earth has and will continue to change. There is more than ample proof of that.
Where we disagree is to
1) Whether man is "causing" (or even has any effect) on it.
2) What (if anything) can and/or should be done about it.
3) Whether if it does "change" that it will be "bad" or worse than now. In fact, there's a good chance, based on the historical record, it could actually be "better".
Because,
4) We don't even know what "normal" climate is for earth. (The planets been around for 4 billion +/- years and we have 100-110 years of weather data.)