Read all of this long piece from Bill McKibben in Rolling Stone.
Short version: there are four numbers that count in the global warming debate. 2, 565, 2,795 and 27.
Two degrees celsius is the maximum warming experts agree we can handle without calamity. 565 gigatons is the most we can still put into the atmosphere and have any chance of staying below 2 degrees warming. 2,795 gigatons is the amount of carbon locked up in the known and exploitable reserves of oil, gas and coal owned by energy companies and petro-states – five times higher an amount than it is even close to safe to release. $27 trillion is the current worth of those reserves, 80% of which value must stay below ground if we want to survive but of course none of which those companies want to pass up and write off. Right there is the crux of the dystopic future we’re staring in the face.