Depletion of the global carbon budget: a user cost approach

The Fifth IPCC Assessment Report estimates the world's ‘carbon budget’, which is the cumulative amount of anthropogenic CO2 emissions limiting global warming below 2°C. We model this carbon budget as a resource asset depleted by annual GHG emissions, and estimate the user cost associated with depletion. For constant emissions, social welfare increases US$3.3 trillion (6 per cent of global GDP) over the business as usual scenario of growing emissions, and the carbon budget's lifetime increases from 18 to 21 years. For declining emissions, the gain is US$10.4 trillion (19 per cent of global GDP), and the budget's lifetime is 30 years. Extending indefinitely the lifetime of the carbon budget would require emissions to fall exponentially by 4.8 per cent or more. Although the Paris Agreement abatement pledges will generate social gains of US$2–2.5 trillion (4–5 per cent of world GDP), they are insufficient to prevent depletion of the 2°C global carbon budget by 2030.