This report provides a summary of the workshop on common metrics to calculate the carbon dioxide equivalence of greenhouse gases, which was held on 3 and 4 April 2012 in Bonn, Germany. At the workshop, participants from Parties and the scientific community shared information and their views on four topics: uncertainties; new and refined areas or metrics; policy goals; and the relationship between policy frameworks and metrics. In addition, representatives of the Intergovernmental Panel on Climate Change (IPCC) Working Group I and Working Group III provided information on the status of the work on metrics that the IPCC is developing under the Fifth Assessment Report of the IPCC