We describe an empirical model of global climate that represents variations in radiative forcing due to GHGs, tropospheric aerosols, total solar irradiance, ENSO, volcanic aerosols, the strength of the Atlantic Meridional Overturning Circulation (AMOC), and ocean heat uptake. We suggest cooling caused by major volcanic eruptions has been overestimated by about a factor of 2 due to prior neglect of variations in the strength of the AMOC. The model is used to derive the sensitivity of Earth’s global average temperature to human induced radiative forcing of climate. We then project how much Earth will warm during the next four decades based on this empirical climate sensitivity. Warming projected using this approach is considerably smaller than that forecast by most of the CMIP5 models used in the upcoming IPCC report.