Our food production is driven by fossil fuels. Everything from the farm equipment to the fertilizers we spread to the trucks we ship it in are powered by fossil fuels. When we run out of fossil fuels, we better have a back up energy source (or sources) ready, because our food production will plummet if not. So will basically every industry, since they all depend on cheap transport and automation at this time. So we'll all starve while the economy collapses around us and our infrastructure falls apart as we have neither the money nor the energy supplies to fix it.

Yeah, our dependence on fossil fuels is a huge problem, and not just because of climate change (which might also kill us).