It depends a lot on the “decision” of course.
Consider WWII - you could say that the U.S. “decided” to sink huge amounts of national effort and treasure into forcing Germany and Japan to submit within less than four years. If we had a societal shift on the magnitude of the change in our national consensus after Pearl Harbor, what would be possible?
There’s one article on what such a switch would take:
It’s two years old, but I wouldn’t be surprised if the target was still achievable.
The basic idea is to invest in huge changes to infrastructure and productive capacity for the first 3-5 years, to the point where everything using fossil fuels that wears out is replaced by something using electricity, then those sectors ramp up more slowly and steadily until existing older appliances, autos, heaters, etc. can be replaced proactively.
Generation and transmission infrastructure are also ramped up quickly to start, then more slowly (but still rapidly) as needed.
His solutions rely on no new technological breakthroughs - only deployment of existing technologies at the kind of scale necessary to transition the US to 20% of current fossil fuel use by 2035, and to zero by 2050.
But it does require a mandate - you can’t do it all with incentives. So a command economy, much like in World War II, would be needed. Of course, the invisible hand of the market would not have won the war, either, no matter how many incentives had been dangled in front of people to convince them to make the changes necessary.
On the other hand, it’s a less-costly task than winning WWII - 1.2xGDP, rather than 1.9x for the war. Also, you’d have 25 million people engaged in something fundamentally productive, rather than 15 million people looking to destroy enemy soldiers and industry to bring a war to a close.
Interestingly enough, because of the improved efficiency of electricity over fossil fuels, over half of US energy use goes away completely with no loss in terms of what is delivered - energy that would be used to explore, collect, transport and refine fossil fuels is no longer needed, of course, and using renewables instead of fossil fuels to generate electricity or operate cars reduces losses due to waste heat.