Better models are rapidly defining the uncertainties ahead, says leading climate scientist Ronald Prinn. - The most definitive scientific assessment of global warming to date, a report released earlier this month from the Intergovernmental Panel on Climate Change (IPCC), concluded with "very high confidence" that humans are contributing significantly to global warming. The report also precisely defines the scientific uncertainties concerning the extent, impacts, and timing of global warming. Ronald Prinn, professor of atmospheric chemistry at MIT and one of the lead authors of the report, says that estimating and understanding these uncertainties is key to evaluating climate data and to deciding on a course of action. Prinn, a leading climate scientist and the director of a worldwide project that carefully monitors the amounts of dozens of greenhouse gases, recently sat down with Technology Review to explain why climate-change science is uncertain, how technology is reducing that uncertainty, and what challenges remain.