>At what point does this become so scary that something happens to increase the taxes on fossil fuels so that consumption will go down?

You're jumping to conclusions on the actual solution to the problem.

I suggest unpacking this problem a bit more. Given the time scales, and potential delay between addition of CO2 into the atmosphere and consequence, I imagine that we should also be thinking "How do we adjust to our new climate?". "Taxes, now" is short sighted.