Would a phaseout of hydrofluorocarbons avoid half a degree of global warming?

In a recent “Daily on Energy” report for the Washington Examiner, Josh Siegel and Abby Smith reported: “This morning, the EPA unveiled a proposal to begin limiting potent greenhouse gas coolants known as hydrofluorocarbons, or HFCs. It’s a significant step to curb climate change, as phasing down HFCs could help avoid roughly 0.5 degrees Celsius of warming.”

The claim that a phaseout of HFCs would reduce future warming by 0.5 C is the conventional wisdom, and like many such assertions accepted among Beltway types, it is based upon dubious foundations and assumptions.