The New Climate Institute has a study showing how we can hit 2 degrees without carbon capture or geo-engineering. It's painful, but possible.

3 degrees basically requires countries to meet their commitments. Which for the developing world basically means net zero electricity generation by 2035, 99% of new vehicle sales being EV by 2030 and no new fossil heating in a similar time frame. That's 3/4 of the major emitters. Those are the "easy" ones, since those 3 changes all save money over the medium term. Some sort of technological or social miracle in the 4th (agriculture, especially meat) would give us a lot more slack.