I disagree that oil will maintain close to its percentage of energy sector for the next 40 years. There were people saying the same shit you are about coal 20 years ago. And, yes, cheaper natural gas is part of coal's waning, but that does not tell the whole story. "Best available technology" for controlling NOx and heavy metals has pushed out a lot of old plants - both on the utility scale and industrial scale. I had a client on the industrial side who basically got his coal for free, but switched to gas because there was no way he was going to retrofit his stack to handle the new requirements. Evolving emission requirements definitely affect what the cut will be, and it is just plain shortsighted to believe that those emission requirements will not tilt against oil in the next 40 years.
As far as "spending money," we need to spend money regardless. The options are 1) let some cities/countries get flooded losing those investments, 2) spend money on mitigation efforts, like sea walls and pumping stations, 3) reduce CO2 production. In reality, it will be a combo of the three. The US government is already spending 100s of millions of dollars relocating residents of low lying towns in Louisiana and Alaska, abandoning the old towns. We are already spending money on mitigation efforts. And, we are spending money on pushing renewables. There is a problem, and status quo is not a free solution. I favor a revenue neutral carbon dividend so that there is some economic balance between these options on the market, rather than expecting a lobbyist controlled Congress come up with prescriptive solution that doesn't have corporate pork and loopholes.