As Texas dries up, Montana burns up and the North Pole melts, Mainers recalling the cool, wet summer may wonder what is happening with global warming. Last month, in Portugal, I met with two hundred other scientists putting together one of the three reports that will constitute the third assessment of climate change when issued next May. These assessments, completed every five years, fulfill a mandate of the Framework Convention on Climate Change. Signed by 165 nations, they report on the state of the science with which to judge whether there is “dangerous anthropogenic interference with the climate system.” The two thousand or so authors and reviewers of the full report work in three groups. The first group tries to assess and predict changes in climate, the second group (in which I work) assesses the potential impacts of such change on natural ecosystems and human activities, and the third addresses actions that might be taken to prevent dangerous climate change.