There’s the theory of “peak oil” that people were freaking out about for a while. Well production follows something like a bell-curve. The idea was that we’re so dependant on oil, when world oil production starts declining, human population will be forced to decline with it. However, technology like fracking/horizontal drilling has opened up new, previously unavailable reserves; and cheap renewables are easing demand. We won’t run out per-se, but the energy needed to extract more will continue to increase (barring more technological developments). Oil companies are now predicting a demand-driven peak in oil consumption.

Modern agriculture is still heavily dependant in fossil fuels (fertilizer, pesticides, machinery, transportation, refrigeration), so oil and gas prices almost directly determine food prices. We should probably do something about that. And the greenhouse gas thing too.

I think I’ve heard someone say that there are enough fossil fuel reserves to burn to make the planet uninhabitable for humans.