Fact 1: Earth naturally warms and cools in cycles due to an elliptical oscillation in it's orbit. I think it's every 15,000 years or thereabouts.
Fact 2: Humans are producing gasses that warm the environment.
Fact 3: Global Warming occurs naturally, but humans are accelerating the process by which this happens.
There's not really much else to say. It's happening, and we're making it worse. If you doubt it, you've got your head in the sand.