Fossil fuels are responsible for a majority of our current heat and electricity generation as well as logistics for medications and emergency transportation.

We technically could transition, but doing so would be massively expensive (whether we went with nuclear or renewables), and some industries would simply not be cost effective or would be eliminated entirely.

The consequence of that cost is the stress of financial burden and a slower economy- leading to a spike in suicide and all manner of diseases that can be induced by such stress.

Alternatively, massive taxation and wealth redistribution schemes could be tried to alleviate the self-inflicted poverty, but it would require rewriting the laws and constitutions of many countries to do so effectively across the world, and there's no telling what the consequences of that would be.