1) Intergovernmental Panel on Climate Change (IPCC), Fourth Assessment Report (AR4), Working Group 1 (WG1), Chapter 2, Changes in Atmospheric Constituents and in Radiative Forcing, Table 2.14, page 212, https://www.ipcc.ch/report/ar4/syr/
2) US Environmental Protection Agency, Clean Energy, Calculations and References, http://www.epa.gov/cleanenergy/energy-resources/refs.html