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Future Energy – UCL ISR


Perspectives on low-carbon future energy systems and sustainable development



By Christophe E McGlade, on 12 March 2015

shale gas extraction © istockphoto

by Dr Christophe McGlade and Prof Paul Ekins, UCL Institute for Sustainable Resources

We have known for some time that to limit global warming, some of the world’s fossil fuel reserves are going to have to stay in the ground. All of the carbon dioxide that would result from burning current fossil fuel reserves is around three times the amount that gives us a decent chance of staying below the 2oC threshold (the temperature rise accepted by the international community as associated with the possible onset of dangerous climate change).

Until recently people therefore frequently reported that two thirds of fossil fuels globally were ‘unburnable’. While it’s possible to get lots of interesting insights from this simple finding, this treats all the fossil fuels as the same. This is too simplistic.

The CO2 emissions that result from burning a tonne of coal are much higher than getting the same amount of energy from gas. Oil also has a much higher energy density than coal or gas, which is why it’s so useful for transporting ourselves, and the things we produce and consume, around our own country and the world.

Our recent Nature paper therefore aimed to differentiate between the fossil fuels we can afford to burn while remaining within the 2°C temperature limit.

We found that a third of oil reserves, half of gas reserves and over 80% of current coal reserves globally should remain in the ground and not be used before 2050 if global warming is to stay below 2°C.

We also disaggregated fossil fuel reserves geographically and showed that the reserves that can and cannot be used are not spread around the world evenly. For example, 260 thousand million barrels oil reserves are not used before 2050 in the Middle East.

This is a huge volume of oil, roughly equivalent to all of the oil reserves held by Saudi Arabia. Meanwhile, the United States, Russia, and Australia all use less than 5% of their coal reserves meaning that over 95% of their coal reserves should remain unburnt, again by 2050. After 2050 the scope for carbon emissions, while staying within the 2oC limit, is much reduced,

We also looked at the development of some of the more ‘unconventional’ sources of fossil fuel. None of the oil and gas resources in the Arctic (which are estimated to be very large) were produced and there is only very low levels of production of the oil sands in Canada. All Arctic resources and 85% of Canadian tar sands reserves should therefore be classified as unburnable.

Given the space constraints for an academic paper it wasn’t possible to put in as much information as we would have liked. One element that we have been asked for a number of times is the differences in production for each of the fossil fuels between our 2oC and one that imposed no carbon constraint.

This scenario, in which the world abandons any efforts to reduce emissions, results in a level of global warming that reaches 4oC by the end of the 21st century (we avoid using the phrase ‘business-as-usual’ for such a scenario -see here for a discussion why). The world would then be hotter than has ever been experienced by humans, with unpredictable, but almost certainly very negative consequences for human societies, in terms of droughts, floods and sea-level rise, to name only three of the most likely impacts.

There is a real difference in coal and oil production between this 4oC scenario and the one which gives us a reasonable chance of staying below 2oC – around 220 billion barrels oil and 290 billion tonnes coal are produced in the 4oC scenario. For coal, this represents a 250% increase in the amount of reserves produced.

However, there is much less difference in gas production between the two scenarios. Gas helps to offset some of the reduction in coal to the extent that up to 2035 gas consumption in the 2oC scenario is actually higher than in the 4oC scenario. This is gas acting as a ‘transition’ fuel to a low-carbon economy. However, for gas to a bridge in this way, there are a number of criteria that need to be satisfied – we have written about this in more detail here.

We also received some critical but constructive feedback on the paper and assumptions we made. We are in the process of writing more detailed responses to these and will post these here as soon as possible.


  • 1
    PeterShepherd8 wrote on 18 March 2015:

    I like the carbon budget analogy because we can talk about fixing the problem using familiar management planning strategy. However I think the argument would benefit by qualifying the carbon budget notion as climate scientists Ken Caldeira and Kirsten Zickfeld have done. (already tweeted you Zickfeld’s carbon budget lecture that makes these key qualifications, now moved to http://www.sfu.ca/video-library/video/179/view.html) I also highly recommend signing up for and at least watching the 15 expert videos from the World Bank’s MOOC “Turn Down the Heat: Why We Must Avoid a 4C Warmer World”, which is being offered again starting April 20. You don’t have to do the assignments, just sign up and watch the videos. https://www.coursera.org/course/warmerworld

    As for setting discount rates, my understanding from corresponding with oceanographer Carol Turley, http://www.pml.ac.uk/People/Science-Staff/Dr-Carol-Turley , she confirmed that the Southern Ocean will be hitting an acid tipping point by the 2040’s. She sent me three of her papers to corroborate this statement. I wrote her after taking the WB MOOC, and watching the video below by another famous oceanographer Richard Feely, who in a video presentation dryly notes the Arctic Ocean Acid Tipping Point will happen in the 2030’s, at 12.5 minutes into @RFeely ‘s video at http://climatestate.com/2014/01/31/is-ocean-acidification-an-open-ocean-syndrome-understanding-anthropogenic-impacts-on-seawater-ph/
    I think I already tweeted you a graph from the WB MOOC of the crashing of coral reefs by expected temperature rise this century. What that didn’t show is the rate of ocean deposition of extra carbon, which is 26 million tonnes per day. This carbon converts to carbonic acid, and crashes zooplankton populations that are the food for fish such as Pacific salmon, https://en.wikipedia.org/wiki/Ocean_acidification#Impacts_on_oceanic_calcifying_organisms . Economic mitigation arguments should take into account that if the colder Arctic ocean can take in more CO2 & thus be seriously debilitated in two decades, and the Southern Ocean similarly one decade later, then it is both foolish and reckless to continue to talk about a 2C carbon budget when at that level we are guaranteed 100% crash of coral reefs globally. I’d be happy to email you this information in fuller format, and material from the World Bank’s MOOC if you are interested to incorporate it into your economic argument. @petershepherd8

  • 2
    PeterShepherd8 wrote on 18 March 2015:

    Correction to my post, it’s 26 million tonnes of CO2, not carbon, that anthropogenic emissions add daily into the ocean, as ~ 27% partition to the ocean.

  • 3
    PeterShepherd8 wrote on 18 March 2015:

    I would sooner my postings be treated as email as I don’t wish to sound as forceful as I have been in them. I do still really like using a carbon budget as an analogy, as I recently took Project Management, which uses the type of language and analysis to break problems down into manageable units to fit in a “work breakdown structure”. My only concern is that the proper qualifiers be used within the budget analogy, as a physical carbon budget has a very different meaning than a financial budget, and this distinction needs to be kept in mind at all times when referring to it as a budget. I can’t think of any medical case where a budget analogy is used. Perhaps with a disease where the pH of human blood needs to remain within 0.1 on a 0 – 14 log scale for a patient to survive. The ocean’s healthy range for pH levels isn’t far off the human scale. May-be diabetics talk about a budget for insulin & glucose? I don’t know, it would be a good question for an MD with overlapping interest in climate change. I’ve seen references to the similarity between ocean/human pH healthy ranges before. For this reason I think economists should look at full range of impacts, not just an innocuous-sounding global mean temperature.

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