There are still some edge cases where a grid-powered, air-source heat pump system MAY have slightly higher carbon emissions than a high efficiency furnace RIGHT NOW. This will happen in very cold climates (which means a lower effective seasonal COP) where the grid is very dirty. That might be an argument for not immediately electrifying.

But these systems also ought to last, with proper maintenance, something like a decade. And we should expect there to be no grids dirty enough to make that same calculus happen a decade from now. If you are replacing right now anyway, there’s nearly no cases where a heat pump isn’t the right choice.

Any if your primary goal is reducing emissions and you can afford it, getting a heat pump system installed in parallel to a traditional furnace (and then only using the furnace on the most brutal days where the COP for the heat pump at its nadir) will still absolutely lower your overall emissions, and probably significantly.