Or the fact that we are still coming off of an Ice Age that lasted for more than 100,000 years, and ended less than 10,000 years ago (Or the little Ice Age that ended in 1850). Several models predict that the average temperature at the END of the last Ice Age was 15-20C lower than today.
Is global warming happening? Yes. Is the human race a contributing factor? Probably to some degree. Is the human race the only cause? No.