A recent paper by Gerhard et al (2001) provides an overview of the position taken by petroleum geologists on the issue of human induced global warming. They appropriately point out that for the long term evolution of the earth it is important to look at major long-term forces driving climate change. However, they discount the voluminous evidence presented by the Intergovernmental Panel on Climate Change suggesting human contributions to recent warming. The final sentence of their paper puts their message in a nutshell: "The nonequilibrium systems that control natural phenomena on earth very likely dwarf man's ability to affect climatic conditions on a global scale."
Reference
Gerhard, L. C., W.E. Harrison, and B. M. Hanson, 2001: Geological Perspectives of Global Climate Change. AAPG Studies in Geology No. 47. American Association of Petroleum Geologists. 15 p.