Rajendra Pachauri turned up the heat on global policymakers in a series of interviews following last week’s meeting of the Intergovernmental Panel on Climate Change in Venice.

Speaking to reporters in New York on Monday, the IPCC chairman credited global leaders with endorsing a goal of holding global warming to 2 degrees Celsius but said countries must now follow up with real action. “The reality is that we have very little time,” Pachauri said. Despite an alarmingly wide gap between developed and developing nations, Pachauri said he remains “cautiously optimistic” that a climate deal will be reached in Copenhagen this December.

Following the IPCC’s fourth assessment in 2007, some experts suggested that the panel should switch gears and begin performing more rapid assessments, but in the end the panel decided to stay the course. Pachauri said the IPCC will begin rolling out its next major assessment as scheduled in 2013.

Reuters summarized some of the major issues that the panel will be digging into. At the top are sea level change, one of the more contentious issues in the fourth assessment, and the role clouds, which are the source of the largest uncertainties in current climate models.