I believe the climate is changing, but the impact of human activities on the climate is where I have doubts. Plus the consequences of said climate change are way overblown by the hysterical media.
Every time a volcano erupts, exponentially more CO2 is released into the atmosphere than in all of human history. Methane is a greenhouse gas, and cows produce a lot of it, but only a few thousand years ago all of the world's grasslands were home to billions of large mammels of various species, all of whom would have produced methane as a byproduct. We've only been able to actually observe the global climate in any meaningful way for 100 years or so. To claim that minor year to year fluctuations are signs of impending climate doom is not just being hysterical, its downright unscientific.
We have very little information about the climate prior to 1900 other than very vague descriptions that are written in history books. We would have to have complete, or at least mostly complete, temperature readings and glacier measurements from prior to the 1800s to have a comparison to today. Climate change doom speakers are essentially asking us to believe that there is a clear difference from the before/after of the industrial age, but they have very little data from the "before" section.