The head of the U.N.'s panel on climate change has urged world governments not to be overcome by hopelessness as they negotiate a new agreement to fight global warming.

Intergovernmental Panel on Climate Change chairman Rajendra Pachauri said Monday that despite the IPCC's own warnings that time is running out, the panel has also suggested actions needed to keep climate change in check.

The IPCC is meeting in Copenhagen this week to adopt the final report in its gigantic assessment of climate change. The report combines three previous IPCC documents, but a leaked draft uses starker language, warning of "severe, pervasive and irreversible" climate impact if the world continues to emit greenhouse gases.

Pachauri called the report a "roadmap" for international climate talks.