New IPCC Report (Part 7)

guest post by Steve Easterbrook

(7) To stay below 2 °C of warming, the world must become carbon negative

Only one of the four future scenarios (RCP2.6) shows us staying below the UN’s commitment to no more than 2 ºC of warming. In RCP2.6, emissions peak soon (within the next decade or so), and then drop fast, under a stronger emissions reduction policy than anyone has ever proposed in international negotiations to date. For example, the post-Kyoto negotiations have looked at targets in the region of 80% reductions in emissions over say a 50 year period. In contrast, the chart below shows something far more ambitious: we need more than 100% emissions reductions. We need to become carbon negative:

(Figure 12.46) a) CO2 emissions for the RCP2.6 scenario (black) and three illustrative modified emission pathways leading to the same warming, b) global temperature change relative to preindustrial for the pathways shown in panel (a).

(Figure 12.46) a) CO2 emissions for the RCP2.6 scenario (black) and three illustrative modified emission pathways leading to the same warming, b) global temperature change relative to preindustrial for the pathways shown in panel (a).

The graph on the left shows four possible CO2 emissions paths that would all deliver the RCP2.6 scenario, while the graph on the right shows the resulting temperature change for these four. They all give similar results for temperature change, but differ in how we go about reducing emissions. For example, the black curve shows CO2 emissions peaking by 2020 at a level barely above today’s, and then dropping steadily until emissions are below zero by about 2070. Two other curves show what happens if emissions peak higher and later: the eventual reduction has to happen much more steeply. The blue dashed curve offers an implausible scenario, so consider it a thought experiment: if we held emissions constant at today’s level, we have exactly 30 years left before we would have to instantly reduce emissions to zero forever.

Notice where the zero point is on the scale on that left-hand graph. Ignoring the unrealistic blue dashed curve, all of these pathways require the world to go net carbon negative sometime soon after mid-century. None of the emissions targets currently being discussed by any government anywhere in the world are sufficient to achieve this. We should be talking about how to become carbon negative.

One further detail. The graph above shows the temperature response staying well under 2°C for all four curves, although the uncertainty band reaches up to 2°C. But note that this analysis deals only with CO2. The other greenhouse gases have to be accounted for too, and together they push the temperature change right up to the 2°C threshold. There’s no margin for error.


You can download all of Climate Change 2013: The Physical Science Basis here. Click below to read any part of this series:

  1. The warming is unequivocal.
  2. Humans caused the majority of it.
  3. The warming is largely irreversible.
  4. Most of the heat is going into the oceans.
  5. Current rates of ocean acidification are unprecedented.
  6. We have to choose which future we want very soon.
  7. To stay below 2°C of warming, the world must become carbon negative.
  8. To stay below 2°C of warming, most fossil fuels must stay buried in the ground.

Climate Change 2013: The Physical Science Basis is also available chapter by chapter here:

  1. Front Matter
  2. Summary for Policymakers
  3. Technical Summary
    1. Supplementary Material

Chapters

  1. Introduction
  2. Observations: Atmosphere and Surface
    1. Supplementary Material
  3. Observations: Ocean
  4. Observations: Cryosphere
    1. Supplementary Material
  5. Information from Paleoclimate Archives
  6. Carbon and Other Biogeochemical Cycles
    1. Supplementary Material
  7. Clouds and Aerosols

    1. Supplementary Material
  8. Anthropogenic and Natural Radiative Forcing
    1. Supplementary Material
  9. Evaluation of Climate Models
  10. Detection and Attribution of Climate Change: from Global to Regional
    1. Supplementary Material
  11. Near-term Climate Change: Projections and Predictability
  12. Long-term Climate Change: Projections, Commitments and Irreversibility
  13. Sea Level Change
    1. Supplementary Material
  14. Climate Phenomena and their Relevance for Future Regional Climate Change
    1. Supplementary Material

Annexes

  1. Annex I: Atlas of Global and Regional Climate Projections
    1. Supplementary Material: RCP2.6, RCP4.5, RCP6.0, RCP8.5
  2. Annex II: Climate System Scenario Tables
  3. Annex III: Glossary
  4. Annex IV: Acronyms
  5. Annex V: Contributors to the WGI Fifth Assessment Report
  6. Annex VI: Expert Reviewers of the WGI Fifth Assessment Report

11 Responses to New IPCC Report (Part 7)

  1. Reblogged this on Hypergeometric and commented:
    Sobering degree of global ambition needed to keep warming below 2 degrees Celsius. This is why I am quite pessimistic regarding natural gas as a “bridge fuel”. Every new fossil fuel-powered utility station being built today, every new piece of energy infrastructure which produces greenhouse gases will need to be retired by 2025-2030 to meet this goal.

    • John Baez says:

      Hypergeometric wrote:

      Sobering degree of global ambition needed to keep warming below 2 degrees Celsius. This is why I am quite pessimistic regarding natural gas as a “bridge fuel”. Every new fossil fuel-powered utility station being built today, every new piece of energy infrastructure which produces greenhouse gases will need to be retired by 2025-2030 to meet this goal.

      Indeed! And that’s not going to happen without government intervention at a level that seems politically unlikely.

      It’s not just natural gas as a bridge fuel that we should be pessimistic about: it’s the whole idea that we’ll meet the deadline to stay below 2 degrees Celsisus. One starts wishing that the climate skeptics were right. If the IPCC were dramatically overestimating the rate future global warming, or overestimating the effects of this warming… then we might have enough time to stop global warming before it’s a disaster.

      In other words: climate skeptics should be more willing to take action than the rest of us, because if their worldview is approximately right it’s a problem we still have time to solve if we hurry up and work hard!

      However, it seems the equilibrium worldview for skeptics is one where the problem is so small we can ignore it completely… except for the ever-pressing need to convince everyone else that they should ignore it too.

  2. MisterX says:

    Why do you post all these articles? Just write that the planet and humans are fucked.

    Greets

    • John Baez says:

      Two main reasons:

      1) A lot of people don’t believe the planet and humans are fucked; it’s important to show people the evidence.

      2) There are many degrees of being fucked. Even if a disaster may be unavoidable, we can lessen the magnitude of the disaster if we take action.

    • We’re most definitely *not* fucked. We understand the physical science and the policy implications very well. We’ve also discovered all this at a remarkable time for the human species – we have all the technology we need to solve the problem, and we have a remarkable communications infrastructure (the internet!) to get this information to people who need it.

      The only real question is whether we can overcome our greed and our petty squabbles, and concentrate on building the clean energy infrastructure needed for a carbon neutral society. There’s still time to achieve this, but we won’t manage it if we sit there and say “we’re fucked”. That’s nothing more than a self-fulfilling prophecy.

      • John Baez says:

        I don’t think we disagree very much—perhaps we disagree about nuances in the meaning of “fucked”. I believe that the future depends heavily on our actions now and that being paralyzed by gloom is just silly. I believe that, realistically, we are headed for bad times. But I believe that there are many degrees of bad times—from slightly bad to really bad to extremely bad—and that, realistically, we have the ability to make a difference.

        • MisterX says:

          Hey, I didn’t expect such good answer to my comment ! Thank you :)

        • I think the more interesting question is not so much what we might mean by ‘fucked’, but what we mean by ‘we’. The impacts of climate change will be disproportionately suffered by the poor, especially those living in equatorial regions. I suspect that a lot of the variability in people’s responses to the science of climate change can be explained by a difference in their ethical thinking. When people think the ‘we’ doesn’t include them, they tend to be much more blasé in their responses to climate change.

  3. John Baez says:

    I posted something about this article on G+, and it triggered a discussion with over 250 comments… many of them very useful and interesting! Check ‘em out.

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