Climate Change: "Many, Many Smoking Guns"

When the UN-organized Intergovernmental Panel on Climate Change (IPCC) presents its projections for global warming and future climate changes tomorrow, the report's hallmark will be a far greater level of certainty and precision than what was expressed in the last IPCC report, issued in 2001. "The certainty is huge," says Andrew Weaver of the University of Victoria in British Columbia, Canada's top climate modeling expert and a coauthor of the new IPCC report.

To be sure, continued warming observed since 2001 is part of that certainty. But climatologists say the bigger factor is the broad accumulation of science over the past six years that has increased the precision with which climate models predict future climate change, debunked alternative hypotheses advanced by skeptics, and identified the footprint of man-made climate change in every corner of the earth.