Fossil fuels are buried biomass. The sun provides 1000 W/M^2 and has for the entire history of the earth. Crude oil is concentrated solar energy in the form of hydrocarbons: carbon chains with two of the four possible carbon bonds devoted to hydrogen with the exception of the ends, which have one more hydrogen. The answer to our energy problems is renewable hydrocarbons. Closed carbon cycle. Sustainable, earth bound fossil fuels aren’t; the earth doesn’t care one way or another, but if we want to continue to thrive here we need to care about atmospheric CO2.