Here is the situation:
1. The atmosphere is holding a little less than the amount of CO2 that brings us to the edge of a 1.5°C temperature rise.
2. There is general agreement that we can whether a 1.5°C temperature rise.
3. There is good agreement that a 2°C rise is risky.
4. Exceeding 2° takes us over-the-cliff and likely means a climate that is out of control.
5. It would mean feet of sea rise.
6. Deadly temperatures for significant parts of the year.
7. Significantly stronger and larger storms and generally a climate much more difficult to deal with. Numbers of cities might well be underwater.
8. How quickly is impossible to predict. Just how much carbon we leave in the atmosphere would of course be important but so would be the dynamics of the climate that we understand less and less.
9. Eventually starvation, drought, disease, migrations result in an out of control world.
10. The biggest unknown is Donald Trump.
11. Donald Trump decides what he wants to believe and then adjusts the facts to fit.
Climate change is a "hoax" most likely because he cannot face the fact that he doesn't understand it. Further it would likely alienate his base.
Consequently he is making the United States, the largest source of carbon dioxide, increase its output of CO2 by reviving the coal industry. This one act could determine the future of the Earth.
So can we hold to 2°? If the United States were on our side I would say we had a good chance. Now I believe we have no chance. Nevertheless we need to to try, but psychologicaly it is difficult if you are aware how small are your chances for success.
The other unknown, and I suspect a large one, is just what are the possibilities of negative emission with the most recent technologies, or with the development of new technologies. The last detailed comparison I am aware of was done in 2007.
We need a unified, dedicated effort to analyze the various approaches, develop and look for new ones, and calculate the cost and time to implement. There is great urgency and although I believe Europe (and possibly China) could do it I am not aware of any such proposal.
Below are two probably long shot approaches: the artificial leaf and what I call the magic rocks. The artificial leaf has been under development for 50 years or so. The rocks, I believe, are a newer approach. For the leaf, it may seem hopeless, but as a counter example the recent gravity wave project took 50 years but worked fantastically well. It did have some of the greatest minds behind it, but it is an object lessen in not jumping to conclusions.
The next question is can we meet the Paris accords (which are likely inadequate for 2°) with the US increasing its output of CO2. The answer, barring a miracle of some kind, is no. Why? No one is keeping their promises. The US backed out and is increasing its output of CO2. Together this is doom, and D. Trump can go down in history as the man who destroyed the earth. He has no comprehension of the situation (which we all know) and it feels to me like I am sitting in a horror movie.
There seems to me, as I have called "denialism," an almost universal disconnect. A bullet has been fired at our heads and we don't feel the need to duck.