Is #1o5C #ParisAgreement temperature pathway possible?

At COP21 in Paris we committed to a temperature target of well below 2 degrees C and aspire to limit global warming to 1.5C, and to decarbonize after 2050. We need to examine pathways to 1.5C to see if it is possible. Dr Joeri Rogelj is one of the few researchers who has studied 1.5C pathways.


  1. This seminar was put on by the Australian-German Climate Energy College at Melbourne University.
    So what will it take to achieve 1.5C? Is it possible?
  2. From the seminar advertising:
    "With the Paris Agreement, the world decided to pursue best efforts to limit warming to below 1.5C, partly because climate impacts around 2C are considered too risky and too high by many. This seminar will put a spotlight on the mitigation side, i.e. how much and how quickly would emissions need to be reduced to still have a chance of keeping or returning warming to below 1.5C relative to pre-industrial levels.

    "How does a roadmap towards a 1.5C future differ from one for 2C? How big is the task of negative emission technologies, such as biomass and CCS.

    "In this seminar Joeri Rogelj will present the latest scientific literature on 1.5C emission scenarios, abatement costs, mitigation technologies, and carbon budgets.

    "After Joeri Rogelj's presentation, Erwin Jackson, Deputy Director of the Climate Institute, will provide a debate contribution in regard to the Paris decision on 1.5C and Australian and international climate policy.
  3. Melbourne author of 'Climate Code Red' and activist David Spratt (see Climate Code Red blog) made this summary, emailed to me, based upon Rogelj's May 2015 paper - Energy system transformations for limiting end-of-century warming to below 1.5 °C (abstract), his seminar talk, plus questions and conversation at the end.
  4. * The 1.5C scenario is a 50% scenario, that is 50% of not exceeding 1.5C and 50% of exceeding it.
    * This scenario has a rough 33% chance of exceeding 2C and ~10% chance of exceeding 3C.
    * ALL 1.5C scenarios involve "overshoot" of target and then cooling back to target by 2100 using drawdown.
    * The overshoot is up to 1.7C (see diagram, left, vertical blue dashed line)
  5. * The carbon budget for 1.5C scenario is 200–415 GtCO2 from 2011 to 2100.
    * Given we are doing around 40 GtCO2 per year at the moment, the budget from 2016 is ~0-200 GtCO2
    * In other words, as of now there is no carbon budget left for 1.5C for even a 50% chance of exceeding the target by 2100
  6. * In other words, from now on for 1.5C we have to draw down every ton of carbon we emit.
    * The 1.5C scenario with overshoot requires net zero emission by 2045-2060. If emissions follow on or near the Paris path to 2030, the 1.5C scenario is not feasible.
  7. * The 1.5C with overshoot requires large drawdown mainly using BECCS. By ~2050 this is 15GtCO2e or approx 4GtC. BECCS yields around 1tC/per year/hectare, so this implies biomass from around 4 billion hectares of land. By way of comparison, the total land applied to cropping globally is presently around 3 billion hectare. This is a huge issue, let alone whether sequestration is safe and economic.
  8. How the seminar progressed on Twitter