McKinsey&Company
Whilst leaders in many nations discuss ambitious targets for reducing emissions of greenhouse gases (GHGs), there is also an intense debate underway regarding the technical and economic feasibility of different target levels, what emission reduction opportunities should be pursued, and the costs of different options for meeting the targets.
Download the report here (20 pages):
http://www.epa.gov/statelocalclimate/documents/pdf/mckinsey_summary_11-19-09.pdf