Global carbon budget for a two-degree world

The carbon budget refers to the maximum quantity of carbon which can be released to maintain a 50 percent probability of global average temperature rise remaining
below two-degrees celcius (the target set within the UN Paris climate agreement). This has been measured relative to the quantity of carbon which would be released if
all fossil fuel reserves were burned without the use of carbon capture and storage (CCS) technology. The difference between the two is defined as 'unburnable
carbon'.