I thought the 1.5 target was a pipe dream, and counter-productive b/c it counseled against feasible policies.
But 3+ degree increase would be a worldwide crisis by 2100, 4+ could be close to extinction. Kiss Florida goodbye, and hope when the Atlantic circulation stops, there aren't drastic impacts.
Of course we really don't know what will happen, but if there's a credible downside which is that huge, your grandchildren should kill you and junk your car!
As far as the rest of the world, India and China are by far the biggest emitters now, China won't be in a couple decades, as they're heavily subsidizing renewables. I'm in favor of LNG exports b/c I believe you focus on incremental steps, first phase out coal by making NG a better choice, then phase out NG in favor of 2nd and 3rd generation renewables. Replace ICEs with electric cars (the Chinese will subsidize this for the 3rd world through cheap electric cars), and use electricity where possible in industrial processes.
Of course government has to lead the way, I'd prefer a carbon tax (I also want a VAT and increase the safety net, not just to help the poor and working class, but separate health care from jobs so people have more freedom to move). Subsidies are a 3rd best solution, but there's what works on the blackboard, and then there's political reality.