The point is that upfront investment cost of developing industry specific carbon neutral solution doesn't have uniform ROI and can be (either economically or po

The point is that upfront investment cost of developing industry specific carbon neutral solution doesn't have uniform ROI and can be (either economically or politically) quite expensive or sometime infeasible. This is an extremely long tail problem and we do need a more general solution applicable even after we exhausted all the low hanging fruits. This is what "upper bound" means in the parent post. So in the ideal scenario, it's more like we eliminate 80% of low hanging emission sources, significant reduce 15% of them and negate the rest with carbon removal to achieve carbon neutrality. In addition to this, removing historical accumulated carbon is also pretty important. The expected cumulative damage at the point of 2050 will be catastrophic even in the most optimistic projection.