[mordymoop]

This only works up to a certain volume. The world economy requires about 38 billion barrels of oil per year. If you processed 100% of all grain, sugar crop, tuber and oilseed on Earth into liquid fuel, leaving zero for food, you'd get about 6 billion barrels of oil-equivalent in liquid fuels. Since it has to compete with food, the actual number would be much lower. It's not even close to being able to sustain our civilization.

[fpoling]

There is absolutely enough coal to make liquid fuel for the current civilization. But if oil/gas would not exist, then electrical cars would be on the road much earlier as burning coal to produce electricity is much more efficient then converting it into liquid fuel to burn in a car engine. As electrical cars produces roughly the same amount of CO2 when using electricity from coal as ICE car running on gasoline, the climate impact would be roughly the same.

Then in a hypothetical scenario of 20th century without oil/natural gas nuclear energy would be much more widespread at this point and CO2 impact would be lower.