The case for global climate change due to human activity has been developing over the last few decades. There are many excellent sources on this topic, and this webpage is not intended to be  complete analysis of the case, its level of certainty, or its various aspects. 

At the same time, background information on the topic is provided in the article below.

Reference

Karl, T., el al. (2003). Modern Global Climate Change. Science, 302, 1719; DOI: 10.1126/science1090228