More time …. really?

A recent paper about [e]mission budgets and pathways consistent with limiting warming to 1.5 °C essentially argues that it is still possible to follow an emission pathway that will give us a good chance of keeping warming below 1.5oC. More specifically, if we can keep total emissions from 2015 to below 200 – 250GtC (depending on what we do with regards to non-CO2 emissions) then we will have about a 66% chance of keeping warming to below 1.5oC.

Unfortunately, this has been interpreted in some circles as suggesting that we can relax a bit because we have more time than we had previously thought. This was mainly based on previous analyses suggesting that the carbon budget that would keep warming below 1.5oC was only about 50GtC (from 2015). Let’s be clear about something; we’re currently emitting 10GtC per year. Whether the budget is 50GtC, or 250GtC, we pretty much have to start reducing emissions now, and get them to zero as soon as we realistically can. Of course, if it is 250GtC, then that will be easier to achieve than if it is 50GtC, but it doesn’t really change what we should do, assuming that we do want to achieve this target. Personally, I think the correct framing is: if this study is correct, and if we keep total emissions from 2015 to below 200-250GtC, we might keep warming to below 1.5C.

However, I think there are some potential issues with this paper. One is that they’re assuming an 1861-1880 baseline from which they’re estimating the observed temperature change. There are arguments (here, for example) suggesting that to properly capture the warming we should use an earlier baseline, which would lead to us having warmed more than if we use a late 1800s baseline. Hence, we may already be closer to 1.5oC than this paper suggests.

Credit: Millar et al. (2017)

Another potential issue is that a key factor in their analysis is a potential mismatch between the model warming and the observed warming (see figure on right). Their argument is that after emitting as much as we have to date, the models predict more warming than has been observed. Hence, the models are predicting a smaller carbon budget than may actually be the case.

One problem is that there have been a number of recent studies reconciling the supposed model/observation discrepancy. These include updating the forcings and doing a proper apples-to-apples comparison by using blended temperatures (i.e., climate model output is typically air temperatures, while observations are a combination of air and sea-surface). So, there may not even be as big a discrepancy as suggested in this paper.

However, even if there is a discrepancy between the models and the observations, we still don’t know if this is because the models are really running too hot, or because some internal process (the pattern of sea surface warming, for example) has suppressed some of the forced warming. If the latter, then we’d expect the observations to catch up to the models at some point in the future and, hence, the initial model estimates for the carbon budget may not be too low.

So, I would certainly be cautious about assuming that the carbon budget is indeed as high as suggested by this new paper. However, in some sense it doesn’t make a great deal of difference. Even if the carbon budget that would give us a 66% chance of staying below 1.5C is 250GtC (or ~400GtC for 2oC) achieving this is going to require pretty drastic emission cuts starting as soon as we possibly can. It certainly doesn’t, in my view, imply that we can now sit back, relax, and wait a few more years before seriously thinking about how to reduce our emissions.

Ambitious 1.5C Paris climate target is still possible, new analysis shows – Guardian.
Guest post: Why the 1.5C warming limit is not yet a geophysical impossibility – Carbon Brief.
Study saying climate change poses less of a threat than first thought ‘has been dangerously misinterpreted,’ academics warn – Evening Standard.
Did limiting global warming to 1.5C just get easier – Climate Home.
Did 1.5C suddenly get easier? – Glen Peters.
Have scientists really admitted climate change sceptics are right? – The Independent.

This entry was posted in Climate change, Climate sensitivity, Global warming, IPCC, Research, Uncategorized and tagged , , , , , , . Bookmark the permalink.

38 Responses to More time …. really?

  1. I think when citizens hear this news, they primarily take away a message like: “We have to do something by 2100, or 2050 or2030.” which is of course not the correct message. I think the correct message is “We all have to do something right now that is going to be very difficult.”

    The true scientific discussion is generally pretty complicated, conditional and nuanced, but that discussion is hard to follow for non-scientists/citizens and is easily spun. It seems we have lost forward motion and may now be wedged between a granite-like substance and a very dense material.

    How are we doing with CO2 you might ask?

    August CO2
    August 2017: 405.07 ppm
    August 2016: 402.25 ppm

    I would say, not too good.



  2. small,

    I think when citizens hear this news, they primarily take away a message like: “We have to do something by 2100, or 2050 or2030.

    Yes, I agree. I think many think that what matters is eventually getting net emissions to zero. What isn’t always appreciated is that a key factor is how much we emit in total. Hence, we need to get emissions to zero while also not exceeding some total amount of carbon emitted (depending on whatever our target is).

  3. @ATTP,

    Thanks for this. This is a complicated one. I’d recommend people read Glen Peters initial reaction to it linked at the bottom of @ATTP’s post.

  4. Joshua says:

    I think we can dismiss this paper as it is based on modeling, and because it is written by alarmist, one-world hoaxters.

    At least that is what they’re saying in the “skept-o-sphere” and the right wing blogosphere, anyway, right?


  5. Steven Mosher says:

    “The true scientific discussion is generally pretty complicated, conditional and nuanced, but that discussion is hard to follow for non-scientists/citizens and is easily spun.’

    ya 3D chess under water.

  6. verytallguy says:

    A couple of thoughts:

    Firstly, *if* we were implementing a plan to get to zero carbon in 5 years then this would be very significant indeed. As, in reality we’re doing next to nothing and have no realistic plan to get to zero carbon ever, it has limited relevance.

    Secondly, the reason there’s such a large reduction in the headline figure is that it’s looking at a threshold (1.5C) and that is quite close to what is already committed. This is part of a wider, and in my opinion at least, unhelpful binary approach to climate change: it’s either solved or it’s apocalyptic. The reality is that there is a continuum from where we are now, and with every bit of extra warming comes extra danger.

    Regardless as to whether this carbon budget or other versions are “accurate”, we need to implement a realistic action plan. I see no real sign of that; whilst the rate of carbon emissions has apparently slowed in the last couple of years, the atmospheric CO2 continues to rise unabated.

  7. Firstly, *if* we were implementing a plan to get to zero carbon in 5 years then this would be very significant indeed. As, in reality we’re doing next to nothing and have no realistic plan to get to zero carbon ever, it has limited relevance.

    That’s essentially my view. Limiting total emissions (from 2015) to 50GtC is virtually impossible. Limiting it to 250GtC is going to be difficult. If we achieved the latter, that would be quite impressive and – if we did so – it’s possible that we might still limit warming to around 1.5oC. At the end of the day, all of these studies seem to indicate that if we want to limit warming to something around 1.5 – 2oC we’d better start reducing our emissions. As you say, we’re pretty much doing next to nothing.

  8. izen says:

    The take-away message from this research in the Brietbart, Fox, Times end of the meja is that we can burn all the oil, and probably a lot of coal and temps wont get above 2degC over pre-industrial.

    With the upper range taken as the definitive value, it is reported that we can put another 880billion Gtn CO2 into the atmosphere. This is the final nail, the death of alarmism, ““It’s the first official confirmation we’ve had that CO2 is not as big a driver of climate change as the computer models have claimed; and it’s the first official admission that the planet is not warming dangerously.”

    How does this square with climate sensitivity? Is it another method of selecting observational periods to alter the trend slope from which you derive ‘sensitivity’?

    The claim is that the ‘wrong’ IPCC carbon budget would require a further 0.5degC warming in less than a decade. Which is of course impossible.

    Unless you cherry pick…

  9. 50% of our soil will be gone in 30 years. 50% of humanity will be short of water in 20 years.
    Food shortages comin quick. Superstorms and meter per decade sea level rise by 2050 says James Hansen.

    Climate sensitivity and a mythical carbon budgets are fudged to justify BAU.

  10. David B. Benson says:

    I still opine that the climate state is inexorably headed for that of the early to mid Eocene. Eventually at least 25 meters higher sea stand and global temperature about 2–3 °C higher than now. Not good as nobody is considering removing the excess carbon dioxide.

  11. David,
    Given the Earth System Sensitivity (maybe 1.5 times the ECS) that is probably where we are indeed headed. Timescale of many centuries for the sea level rise, but still….

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  13. David B. Benson says:


    Pliocene, not Eocene.

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  15. There’s some discussion and calculation regarding “are climate models running hot” over at the Climate Lab Book.

  16. There’s been an interesting discussion on Twitter involving (amongst others) Gavin Schmidt, Ed Hawkins, Karsten Haustein, Zeke Hausfather and Piers Forster (one of the authors). One thing is that when their paper was submitted it only considered to the end of 2014. It took a while to get accepted and things did change a bit in that time. However, maybe a key thing is that how much warming we’ve already experienced does differ by a few tenths of a degree C depending on the dataset used. Their paper really gives a carbon budget for 0.6C of future warming. If Berkeley Earth is correct, then that budget would give us a 66% chance of staying below 1.7C. If HadCRUT4 is correct, then it 66% chance of staying below 1.5C. This also does not take into account from when we should be basing the temperature change. Is it the mid-1800s, or is it actual pre-industrial. If the latter, then that adds about another 0.1C to how much we’ve warmed.

    It’s all rather complicated and doesn’t really change – in my view – the general conclusion that if we want to keep warming below some level between 1.5C and 2C, we’d better start reducing emissions soon and aim to get net emissions to zero as soon as we realistically can.

  17. Not good as nobody is considering removing the excess carbon dioxide.

    There’s work being done and there is discussion of its legal, diplomatic, and ethical ramifications, but, yes, no one that I know is proposing funds to try scale-ups. That is unfortunate given the prominence of negative emissions later this century in the UNFCCC COP21 proposals. On the other hand, no one is going to start doing this until emissions get to 20% of present, apparently.

    There’s a lot to talk about. I’m hearing and reading of increasingly mixed feelings in some quarters about rolling out large scale solar farms for fear of ecosystem impacts. I personally think that’s rearranging the deck chairs on the Titanic, but it’s a thing. In comparison, rolling out a couple of million Lackner CO2 capture units or planting hundreds of square kilometers with Jatropha curcas is bound to have ecosystem repercussions. Doing enough Jatropha might even affect the local climate, and I’m not sure how the albedo modification in the desert trades off.

  18. izen says:

    The gogle search AI is clearly developing a sense of humour.
    News returns on this subject give this high in the list.

    ” A revealing new science paper published in the science journal “Nature Geoscience” has just fully exposed the climate change hoax. The paper, a confession authored by climate change alarmists Myles R. Allen, Richard J. Millar, and others, reveals that global warming climate models are flat wrong, having been biased and crafted towards “worst case” warming predictions that were designed to alarm and scare the general public.”

    It goes on to explain how the warming scare “was based on faulty, fraudulently programmed software models”

    However it hedges its bets. Conceding that if CO2 did cause drastic warming, – this would be a good thing.

    “A tropical Antarctica would be a great thing for the world. …
    Antarctica was once a tropical continent, before the biblical global flood of Noah, in a time when the Earth’s temperatures were regulated throughout the globe.”

    That, apparently, is why there are dinnosaur bones there.
    I know this is an outlier. But it is part of the Overton window on the subject. And the confluence of AGW denial and YEC is fun.

    If this paper is based on pre-2014 temps, does that mean that ~0.2 degC of the ‘missing’ modelled rise has happened since it was written ?

  19. JCH says:

    Zeke’s graph:

    What stands out, painfully obvious, are the major La Niña events: 98-01; 07-08;10-12. These took place when the PDO was negative. Vast areas of the Eastern Pacific were very cold. Going forward, there is no way know if the PDO is going to join hands with La Niña events, or, it might instead continue joining hands with El Niño events. Should it do that, you could have a repeat of Izen’s cherrypick: another ~.6 ℃ in ~8 years: a GFDL spring-back warming.

  20. @JCH,

    Re: Zeke’s graph …. Now that’s a nicely done and proper comparison. I was wondering where the uncertainty envelopes were in the Millar, et al chart above! I didn’t say anything because I didn’t fully understand the significance of the time-shifting comments Glen Peters made about these.

  21. John Hartz says:

    ATTP: Two more articles for your listing of Links.

    New climate change calculations could buy the Earth some time — if they’re right by Chris Mooney, Energy & Environment, Washington Post, Sep 18, 2017

    So much for the climate change ‘hoax’ by Steven Stomberg, Washington Post, Sep 19, 2017

  22. verytallguy says:

    Zeke’s post is an excellent example of Brandolini’s law, the “bullshit asymmetry principle”:

    The amount of energy needed to refute bullshit is an order of magnitude bigger than to produce it.

  23. BBD says:

    I’ve kept quiet about this because my reaction to the argument that modelling has overestimated warming so much that the carbon budgets were significantly wrong was WTF? But what do I know?

  24. JCH says:

    Over at CargoCult Etc., any time you see “stay tuned for our next paper”, it means there’s more bullchit in the pipeline.

  25. ‘Zeke’s post is an excellent example of Brandolini’s law, the “bullshit asymmetry principle”:

    The amount of energy needed to refute bullshit is an order of magnitude bigger than to produce it.’

    That’s why we need a bulldozer for Richard Lindzen. To fully unwind his damage will take years.

  26. John Hartz says:

    Too little? Too late?

    Clarification on recent press coverage of our ‘1.5 degrees’ paper in Nature Geoscience</strong Oxford Martin School or the University of Oxford., Sep 21, 2017

    A number of media reports have asserted that our recent study in Nature Geoscience indicates that global temperatures are not rising as fast as predicted by the Intergovernmental Panel on Climate Change (IPCC), and hence that action to reduce greenhouse gas emissions is no longer urgent.

    Both assertions are false.

    Our results are entirely in line with the IPCC’s 2013 prediction that temperatures in the 2020s would be 0.9-1.3 degrees above pre-industrial (See figures 2c and 3a of our article which show the IPCC prediction, our projections, and temperatures of recent years).

    What we have done is to update the implications for the amount of carbon dioxide we can still emit while expecting global temperatures to remain below the Paris Climate Agreement goal of 1.5 degrees. We find that, to likely meet the Paris goal, emission reductions would need to begin immediately and reach zero in less than 40 years’ time.

    While that is not geophysically impossible, to suggest that this means that measures to reduce greenhouse gas emissions are now unnecessary is clearly false.


    Richard J. Millar
    Jan S. Fuglestvedt
    Pierre Friedlingstein
    Joeri Rogelj,
    Michael J. Grubb,
    H. Damon Matthews
    Ragnhild B. Skeie
    Piers M. Forster
    David J. Frame
    Myles R. Allen

    This opinion piece reflects the views of the author, and does not necessarily reflect the position of the Oxford Martin School or the University of Oxford. Any errors or omissions are those of the author.

  27. Steven Mosher says:

    What vtg said.

  28. John Hartz says:

    The best rebuttal article so far?

    The lead paragraphs only…

    The science news media has a pretty simple job: Find facts, and report them. Typically, this entails reading a scientific study, talking to the study’s authors and outside experts, writing, and fact-checking the confusing bits with experts again. But sometimes, the narrative the media wants isn’t actually supported by the study, or the experts. Such is the case with a new paper on climate change.

    The study, published in Nature Geoscience earlier this week, took a stab at trying to figure how much carbon humans can emit before crossing the 1.5 degree Celsius global warming threshold set forth in the Paris Climate Agreement. And it came to a sort of optimistic conclusion: We may have more carbon in the bank than we thought. Other experts were immediately skeptical, but that didn’t stop several outlets from running stories that twisted the study’s key find into a bad parody of itself, suggesting that the “fear of global warming is exaggerated,” and climate change may not be “as threatening as previously thought.”

    Things went totally off the rails from there. “The scientists who produce those doomsday reports for the Intergovernmental Panel on Climate Change have finally come clean—the computer models they’ve been using to predict runaway global warming are wrong,” bloviated The Sun. “Climate alarmists have finally admitted that they’ve got it wrong on global warming,” Breitbart piled on.

    It got so out of hand that the University of Oxford-based researchers released a statement yesterday disavowing the idea that we now longer need to take aggressive action to reduce carbon emissions, followed by a response article in The Guardian this morning.

    New Climate Study Doesn’t Contradict Global Warming, No Matter What Breitbart Says by Maddie Stone Gizmodo, Sep 21, 2017

  29. Everett F Sargent says:

    Figure 2a (on the left hand side) is the key figure as far as I’m concerned. Integrate the blue and green curves, take their difference (350-240=110 gigatonnes over 83 years)

    In other words humanity, must adhere to an RCP 2.6 emissions scenario plus ~1.3 additional gigatonnes per annum (on average over and above RCP 2.6) from 2017 to 2100.

    Don’t look at the BAU black and red curves or RCP 6.0 or RCP 4.5.

    We’ve seen this before, it looks like a breaking wave, when the face goes vertical, it breaks, game over.

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  31. John Hartz says:

    Rahmstorf weighs in…

    Is there really still a chance for staying below 1.5 °C global warming? by Stefan Rahmstorf, Real Climate, Sep 22, 2017

  32. Andrew J Dodds says:

    BBD – your reaction was the same as mine. There isn’t anything substantial there and we are going to blow through the 2 degree budget anyway. And it’s only residual optimism that makes that a 2 and not a 3.

  33. Pingback: Is de opwarming van de aarde nog te beperken tot 1,5°C? | Klimaatverandering

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