Research by the Potsdam Institute calculates that to reduce the chance of exceeding a 2°C global warming to 20% or 1 in 5, the global carbon budget for 2000-2050 is 886 GtCO2.

Minus emissions from the first decade of this century, this leaves a budget of 565 GtCO2 of emissions for the remaining 40 years to 2050.
The fossil fuel reserves held by the top 100 listed coal companies and the top 100 listed oil and gas companies represent potential emissions of 745 GtCO2.
This exceeds the remaining carbon budget of 565 GtCO2 by 180 GtCO2.
This means that using just the listed proportion of reserves in the next 40 years is enough to take us beyond 2°C of global warming.
On top of this further resources are held by state entities.

Given only 20% of the total reserves can be used to stay below 2°C, if this is applied uniformly, then only 149 of the 745 GtCO2 held by listed companies can be used unabated.
Oil, coal and gas investors are thus left exposed to the risk of unburnable carbon.

If the 2°C target is rigorously applied, then up to 80% of declared reserves owned by the world’s largest listed coal, oil and gas companies and their investors would be subject to impairment as these assets become stranded. The economic consequences of having fossil fuels with an emissions value of 180 Giga tonnes CO2 are thus much worse than even the current economic crisis.

Potsdam Institute, 2011