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 0.48 W m^-2 to 0.61 W m^-2) compared to the value in the Intergovernmental Panel on Climate Change (IPCC) 2013 assessment; the 100 year 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 2000 ppm, a value projected to be possible under the extended RCP8.5 scenario.