The other option is that no controls are imposed on burning fossil fuels, and the carbon bubble does not burst until the warming breaks through the two-degree limit and triggers the natural feedbacks that will carry us inexorably up to +6 degrees C. That implies mass death and possibly civilizational collapse by the end of the century, but the fossil fuel reserves will retain their assumed value for the meantime and there will be no financial crash.
Gwynne Dyer: The third option on global warming, 28 Apr 2013

thanks to Sun Spot