I can't answer that for sure and I'm not sure anyone can which is what makes this problem difficult. We have projections about what CO2 levels need to be by a g

I can't answer that for sure and I'm not sure anyone can which is what makes this problem difficult. We have projections about what CO2 levels need to be by a given year to hopefully avoid a 2 degree increase, but when you are dealing with potential global catastrophe it seems crazy to debate minute details and if we try to just do the bare minimum we might still have catastrophe because our estimates were not on the money. The earlier we start the less drastic our measures have to be. Unfortunately aside from pure market forces you can just about write off the USA for the next 4 years (in fact, maybe assume that we are a hostile actor as far as climate change is concerned) which means in 4 years we may not even have as many options and measures will get increasingly drastic (ie, potential energy limits on actual consumers).