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The calculator is based on the Intergovernmental Panel on Climate Change’s (IPCC’s) Model for Assessment of Greenhouse Gas Induced Climate Change (MAGICC). As the documentation illustrates, this model has myriad assumptions about climate. The Climate Calculator focuses on two key assumptions: climate sensitivity and the level of emissions reduction. Scientists generally agree that the Earth’s temperature warms as CO2 emissions increase—the real question is to which degree (no pun intended).
Climate sensitivity measures how much the Earth’s temperature will warm as a result of a doubling of atmospheric CO2 concentration. The emissions-reduction level is the percentage of CO2 emissions that lawmakers would seek to reduce with respect to current emissions. The methodology below contains full details.
The simulations presented in this calculator allow user-selected climate sensitivities between 2℃ and 5℃, stated as the “very likely” range of climate sensitivity according to the IPCC’s Sixth Assessment Report, encompassing the “likely” range of 2.5℃ to 4℃. Although empirical evidence comparing observations to predictions suggests that sensitivities at the lower end of these ranges may indeed be more plausible, Heritage’s Climate Calculator allows users to decide which climate sensitivity they would like to assume and how steep of a reduction in fossil fuel use they would like to see. The results speak for themselves—regardless of the assumptions, the climate impact of CO2–reduction policies is slim to none!