Sure, the current, and well measured trend toward warmer averages could turn around anytime and prove to be just another statistical variation in overall weather patterns. There is clearly a huge amount of human-generated greenhouse gasses in our atmosphere that never existed before, and we are definitely experiencing much higher average global temperatures. And the ice coverage in Greenland and Antartica is lower and shrinking faster than ever measured before. Seems kinda stupid to me to ignore the possibility that we've actually F'ed up our own planet.