As a number of recent studies have emphasized, projected global temperatures will largely be determined by cumulative emissions of greenhouse gas emissions over a given period of time. In a new study published in the journal Nature, researchers Christophe McGlade and Paul Elkins employ a single integrated assessment model that includes estimates of fossil fuel “resources” (defined as remaining ultimately recoverable resources) and “reserves” (defined as resources recoverable under current economic conditions) to determine what portion of coal, oil and natural gas can ultimately be utilized consistent with the objective of keeping temperature increases to 2C above pre-industrial levels.

Among the study’s conclusions:

1. To maintain at least a 50% chance of keeping temperature increases to below 2C, the cumulative remaining global “carbon budget” is approximately 1100 gigatons of carbon dioxide;
2. There is a massive gap between both estimated fossil fuel resources (nearly 11,000 Gt CO2) and reserves (nearly 2,900) and the 1100 gigaton carbon dioxide budget that may be necessary to avoid passing critical temperature thresholds;
3. Under a scenario in which carbon capture and sequestration (CCS) is extensively deployed from 2025 onwards, over 430 billion barrels of oil and 95 trillion cubic meters of gas reserves would have to stay in the ground, translating in half of the oil in the Middle East, and a whopping 75% of Canada’s oil reserves, with its large reserves of bitumen;
   1. 82% of coal reserves will need to remain unburned to not exceed the world’s carbon budget by 2050, with the US and former Soviet Union availing themselves of less than 10% of their reserves
4. If CCS is not widely deployed, utilization of current fossil fuel reserves must be lower, though CCS only increases potential utilization of coal reserves by 6% by 2050;
5. In terms of unconventional oil, natural bitumen utilization in Canada must become “negligible” by 2020, and without CCS, all bitumen production must cease by 2040. Unconventional natural gas fares better, displacing coal in electric and industrial sectors, permitting 50 trillion cubic meters to be burned. However, by 2050, fully 80% of unconventional gas resources in China, India, Africa and the Middle East must remain unburned.

Among the class discussion questions this piece might generate:

1. Given the limited utility of CCS through 2050, does it make sense to press forward with its development?. What are the implications of CCS deployment post-2050 and its significance for carbon budgets?;
2. Should the allocation of “unburned” carbon be actively managed under a set of equitable principles? If yes, what principles should control said allocation?
3. What are the implications of aiming for a better than 50% chance of avoiding exceeding a 2C increase in temperatures?