Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing

New calculations of the radiative forcing (RF) are presented for the three main well‐mixed greenhouse gases, methane, nitrous oxide, and carbon dioxide. Methane’s RF is particularly impacted because of the inclusion of the shortwave forcing; the 1750–2011 RF is about 25% higher (increasing from 0.48Wm to 0.61Wm) compared to the value in the Intergovernmental Panel on Climate Change (IPCC) 2013 assessment; the 100year global warming potential is 14% higher than the IPCC value. We present new simplified expressions to calculate RF. Unlike previous expressions used by IPCC, the new ones include the overlap between CO2 and N2O; for N2O forcing, the CO2 overlap can be as important as the CH4 overlap. The 1750–2011 CO2 RF is within 1% of IPCC’s value but is about 10% higher when CO2 amounts reach 2000ppm, a value projected to be possible under the extended RCP8.5 scenario.