The goal of the Paris Agreement, an international treaty on climate change, is to limit global warming to well below 2 °C and preferably to 1.5 °C above pre-industrial levels. To achieve this goal, the use of fossil fuels, i.e., oil, natural gas, and coal, needs to be limited significantly. This will lead to large parts of existing fossil fuel reserves—currently considered economically viable to extract—remaining in the ground.

Dan Welsby, University College London, UK, and colleagues have estimated the amount of fossil fuels that would need to remain unextracted to allow for a 50 % probability of limiting warming to 1.5 °C. The team used a global energy systems model called “TIMES Integrated Assessment Model at University College London”, or TIAM-UCL, to determine the approximate levels of fossil fuels that would remain “unextractable” in 2050 and 2100. The model describes energy sources, conversion, transport, distribution, and use and simulates changes over time based on minimizing costs.

The team found that based on the reserves in 2018, 58 % of oil, 59 % of fossil methane gas, and 89 % of coal need to remain in the ground in 2050 to achieve a 50 % probability of keeping the global temperature increase to 1.5 °C. By 2100, 43 % of oil, 50 % of fossil methane gas, and 88 % of coal still need to be unextracted. Most of the oil and gas would be used as a chemical feedstock instead of as fuel at this point in time, reducing their carbon footprint.

According to the researchers, these results indicate that the production of fossil fuels would need to peak very soon in many regions of the world to stay with the 1.5 °C limit. This should inform both economic development and policy decisions.

• Unextractable fossil fuels in a 1.5 °C world,
  Dan Welsby, James Price, Steve Pye, Paul Ekins,
  Nature 2021.
  https://doi.org/10.1038/s41586-021-03821-8