The Trump administration's Safer Affordable Fuel-Efficient (SAFE) Vehicles rule is deregulatory compared to the 2012 Obama administration rule it replaces. The SAFE rule increases the stringency of corporate average fuel economy (CAFE) standards by 1.5 percent annually. If still in effect today, the 2012 rule would increase regulatory stringency by 5 percent annually.
California and its allies tout the 2012 rule as a “climate solution” and slam the SAFE rule as a planet wrecker. In fact, both rules are irrelevant to the climate.
Under the SAFE rule, national gasoline consumption and the associated carbon dioxide (CO2) emissions will decline by 32 percent during 2020-50, whereas consumption and emissions would decline by 43 percent under the 2012 rule. Will the SAFE rule's slower rate of decline doom humanity to planetary ruin? Will future generations pay a terrible price for the Trump agencies' deregulatory ambitions? No.
Compared to the 2012 rule, the SAFE rule will, in 2100, increase CO2 concentrations by 0.66 parts per million, global average temperatures by 0.003 of a degree Celsius, and sea levels by 0.06 centimeters — about two-hundredths of an inch. Those numbers come from the Environmental Protection Agency's standard climate policy calculator, a model called MAGICC.
Climate sensitivity — the long-term change in global average surface temperature after a doubling of atmospheric CO2 concentration — is a key variable in climate assessments. The Intergovernmental Panel on Climate Change estimates that climate sensitivity is “likely in the range of 1.5 degrees-4.5 degrees Celsius.”
Accordingly, the Trump agencies used sensitivities of 1.5 to 4.5 degrees Celsius and 6.0 degrees Celsius to estimate the SAFE rule's potential climate effects. Even under the least stringent regulatory option considered (freezing CAFE standards at model year 2020 levels) and assuming the highest sensitivity (6.0 degrees Celsius), the global mean surface temperature in 2100 is only 0.006 of a degree Celsius higher than under the 2012 rule.