[fpoling]

One does need carbohydrates for industrial bootstrap. Germans during WWII produced liquid fuel from coal. Modern version of this process becomes competitive with oil-base fuel around 80 USD/barrel.

Yes, this process is very energy intensive and generates like twice CO2 per energy used. But in a hypothetical world without oil and natural gas it may lead to earlier start with electric cars and renewables so the total amount of CO2 put into atmosphere would probably be the same. Plus, as coal is much more evenly distributed, there would be much less reasons for wars.

[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.

[jfengel]

Just to be pedantic: I think you mean hydrocarbons (just carbon and hydrogen) rather than carbohydrates (carbon, hydrogen, and oxygen).

You could probably do it with carbohydrates (starches, sugars) or related molecules (wood, alcohol). But I'm pretty sure that hydrocarbons is what you intended there, and it's easier to dig that out of the ground.