Gerald Marsh - According to the 2007 IPCC Summary for Policymakers, essentially all of the anthropogenic radiative forcing since 1750 is due to the increase in carbon dioxide concentration. This means that if the sun is responsible for 36-50% of the temperature rise since 1900, the IPCC is using too large a value for its coefficient relating radiative forcing to changes in carbon dioxide concentration. This is important because a smaller value of α reduces the sensitivity of the earth’s climate to increases in carbon dioxide concentrations—a result that has significant policy implications.