A new baseline?

Ed Hawkins and colleagues have a new paper called Estimating changes in global temperature since pre-industrial times, which Ed also discusses in this post. The basic suggestion seems to be that we should probably be defining pre-industrial as the period 1720-1800, rather than as the period 1850-1900, which is often what it is assumed to be. As I understand it this is largely because our emissions probably started in the mid-1700s, rather than the mid-1800s, and that, consequently, there is a some warming that is missed if you define the baseline as being 1850-1900, rather than as 1720-1800.

This has, however, cause some confusion because some are suggesting that this new baseline means that we’re closer to the 2oC limit than we realised, with others claiming that this is not the cause because the limit was defined with respect to a known baseline, and so doesn’t change. However, it almost appears as though noone is entirely clear with respect to what baseline the 2oC limit was defined.

Sometimes, however, a temperature target is also associated with a carbon budget, which is the total mount of carbon we can emit while still giving us a certain chance of remaining below that temperature. As far as I can tell, this is clearly determined relative to when we started emitting, so if the temperature target is relative to a different period, then this would seem to suggest that the temperature target and the carbon budget are not entirely consistent. However, given that the difference is of order 0.1oC and we’re unlikely to set a target more finely than 0.5oC, it’s not clear that we would necessarily change anything. Would we really change the target to 2.1oC if we think that 2oC from 1850-1900 is the “right” target and that there was 0.1oC warming between when we started emitting and this baseline period. I can’t see why.

Something to bear in mind is how much of the carbon budget we have left. As this Carbon Brief post shows, we have about 25 years left at current emissions if we want a 50% chance of staying below 2oC. This seems like rather a tough task and it does seem that a large number of people think it extremely unlikely that we will avoid 2oC of warming. If so, why are people arguing about what the correct baseline should be when we are unlikely to meet the target whatever baseline we use? It would seem to me that what we should be doing now does not depend on whether we use 1850-1900, or 1720-1800.

This isn’t to suggest that the paper isn’t an interesting paper and that being clearer about the baseline wouldn’t be a good idea. I’m just not clear as to what difference it really makes. If we’re already at a stage where we’re going to miss a target however we define the baseline, then apart from some extra clarity, I really can’t see what overall difference this makes. I could, of course, be missing something, so feel free to point it out in the comments if I am.

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24 Responses to A new baseline?

  1. I don’t think it makes any practical difference, but it’s one of those things where it’s helpful to have a precise definition, just so everyone knows where they stand. In my project HELIX (High-End cLimate Impacts and extremes 🙂 ) http://helixclimate.eu/home we are framing the results in terms of levels of global warming (2C, 4C, 6C and now also 1.5C too). It turns out (not too surprisingly) that there are a lot of intricacies in determine exactly what we mean by “2C global warming” and there are lots of (similar) ways this can end up being defined in modelling studies, especially when you have to make inevitably compromises to to the best you can within the computing power and/or research time available. Clearly, it’s useful if everyone uses the same definition, so you can make fair comparisons between different areas of work or between different studies looking at the same thing. I hope that Ed’s paper inspires the authors of the IPCC 1.5C Special Report to make some clear definitions and conventions.

    If anyone’s in Bristol on Wednesday, I’ll be discussing this in a guest seminar in the Geography Dept 🙂 [shameless plug klaxon!]

  2. Magma says:

    I’ll repost my comment from Ed Hawkins blog, originally in response to repeated long-winded fake legalistic carping by Brandon Shellenberger about how this would undercut the Paris agreement. (It’s a very readable paper, by the way.)

    Only reference to “pre-industrial levels” in the text of the Paris Agreement:
    Article 2
    1. (a) Holding the increase in the global average temperature to well below 2 °C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change;

    Hawkins et al. (2017):
    Conclusions & implications
    2. The 1850-1900 period is a reasonable pragmatic surrogate for pre-industrial global mean temperature. The available evidence suggests it was slightly warmer than 1720-1800 by around 0.05 °C, but this is not statistically significant.

  3. I can see the point that ‘pre-industrial’ would, most accurately, be a time before we started emitting greenhouse gasses by powering machinery with fossil fuels. Leaving climate science matters aside, ‘pre-1800’ would therefore appear most logical for the ‘pre-industrial’ description. I tweeted Ed when he was first asking for views about this to say that perhaps we should just continue the convention of a 1850-1900 baseline but instead refer to it as ‘pre-modern industrial’ from now on.

  4. Richard,
    Thanks. Yes, I agree that a clear definition is useful, especially if it’s not even all that clear what it actually is in the first place. Not in Bristol this coming week, unfortunately 😉

  5. To answer your question mark: as far as I am aware there was no previous baseline.

    Even if there were this paper is also not a new baseline because it only informs politicians and they can agree on any baseline they would like in future agreements.

  6. jamesannan says:

    Richard, that has to be one of the most contrived acronyms I’ve ever seen 🙂

  7. Eli Rabett says:

    As Victor says, the primary policy effect this will have is to let policy makers choose any baseline they want, and it is hard to argue against that given the black box claim at the top of the paper:

    “Better defining (or altogether avoiding) the term ‘pre-industrial’ would aid interpretation of internationally agreed global temperature limits and estimation of the required constraints to avoid reaching those limits.”

    It opens a Pandora’s box on the Paris agreement as each nation picks it’s baseline and it would be naive to think that they won’t.

  8. Fergus Brown says:

    If they’d called it High End Climate And Temperature Extremes they’d have had a much neater acronym…

  9. Vinny Burgoo says:

    GAPS (hiGh-end climAte imPacts and extremeS)

  10. No my dearest academic bunny that is not what I wrote.

    There was no agreed upon baseline before. I guess it was initially not necessary yet, we were so far from the limit when the negotiations started. Just like there is not yet an agreement on how it will be monitored that the countries stick to their promises. One step at a time.

    There will only be an agreed upon baseline once politicians agree on one. I would expect that to be in the international COP climate negotiation and not for every country. But who knows what politicians will agree on. They also allowed every country to determine their own set of policies. Logic is not the domain of politics.

  11. john says:

    Would it be possible to settle on a 50 year or 100 year period where the ice balance was in equilibrium, where rainfall events and heatwave events were steady.
    By the same definition cold events were not also outside a range that pushed down global temperatures.
    One problem i see with my suggestion is picking a period on a moving target.

  12. Brave Brandon, also known as Chewbacca, is not Michael Shellenberger, to everyone’s relief including their own.

  13. T-rev says:

    >If so, why are people arguing about what the correct baseline should be when we are unlikely to meet the target whatever baseline we use?

    becasue that’s all most people have left, debate and argument over the minutiae, or Dues ex machina (some miracle technology that can be rolled out ‘in a jiffy’ will save the day) rather than, holycr@p ! I need to cut my emisisons if we’re to stay under 2C. Cognitive dissonance is ubiqutious.

    Apparently the majority of people who see the need for emisions mitigation are waiting for an orderly queue to be formed …. seemingly with the proviso that deniers must reduce thier emissions first 🙂 As an example, Heathrow is to be expanded, Badgery’s Creek Airport in Sydney is to be built, how do those example fit in with emisions being lowered ? Where’s the demand coming from ? deniers only ?

  14. Eli Rabett says:

    Sorry, re-opening a Pandora’s box is not a recommended course of action

  15. @jamesannan

    We are still quite pleased with ourselves that we managed to call our dynamic global vegetation model “Top-down Representation of Interactive Foliage and Flora Including Dynamics” … 🙂

    Also, I was once in a project called “Sustainable Cities: Options for Responding to Climate cHange Impacts and Outcomes” …

    You have to have a bit of light relief sometimes 🙂

  16. this whole thing is framed in a manner that almost guarantees we will hit the 2.0 temp rise. The 20th Century avg global temp was 13.9 degrees C. The avg global temp for 2016 was 14.84 degrees C. When we talk about the 1.5 or 2.0 degrees rise as our limit, I think human psyches automatically accept these targets and start counting down. So if we hit 1.5 degrees soon, we are ahead of schedule? It’s like stepping up to the plate and thinking “don’t strike out, don’t strike out.” pretty different frame than “see the ball, hit the ball” mantra. We should be talking about how to cool the planet. It’s already too warm for our good. Any additional warming is just adding to the catastrophe.

    I see this same problem occurring with discussion of ghg accumulation. We should be talking about how to reduce the CO2 accumulation in the atmosphere instead of talking about slowing the buildup of CO2 (and the other ghg). Michael Mann said in 2014 that we should stay under 405 ppm. Nice, straightforward number. Easy to understand. No confusion about the rate of increase or reports of diminishing emissions, just 405 ppm: we should stay under that.

    Where are we? How are we doing?

    Daily CO2

    January 27, 2017: 405.55 ppm
    January 27, 2016: 403.77 ppm

    We have blown by Mann’s number and we are gaining speed. Any questions? How much global warming do we want? How much global warming can we stand? How about zero now? That is the truth. Any additional warming just increases our problems now. That is a frame of reference that might help us understand that we have to stop the accumulation of GHG and increase of global temp. We have to stop both now. We need to walk these numbers back into the range that provided the more stable and predictable climate that we enjoyed as we evolved in the holocene ear. Let’s make climate great again, let’s go back to the holocene.


  17. angech says:

    A comment I saw on this was “its obviously intended to be ambiguous. If they meant something specific, they would have given a date or even better a temperature.”
    Richard Betts says:
    “I don’t think it makes any practical difference, but it’s one of those things where it’s helpful to have a precise definition, just so everyone knows where they stand.”
    ATTP “However, it almost appears as though no one is entirely clear with respect to what baseline the 2oC limit was defined ”
    “Governments agreed a long-term goal of keeping the increase in global average temperature to well below 2°C above pre-industrial levels;”
    “All of these yield consistent estimates of the approximate magnitude of global warming, which reached about 0.8°C in 2010, twice the magnitude reported in 1981.”
    “absolute SAT – pick one of the available climatologies and add the anomalies (with respect to the proper base period) to it. For the global mean, the most trusted models produce a value of roughly 14°C, i.e. 57.2°F.”
    “November 2015 – Global annual average surface temperature in 2015 is looking set to reach 1°C above the pre-industrial average (as represented by the 1850-1900 reference period) for the first time, according to the HadCRUT4 dataset produced by the Met Office and the Climatic Research Unit at the University of East Anglia”
    Easiest answer is to choose a data set and an implied or actual estimated average global temp for that data set for the 1850-1900 period.
    Lets call it 13.8 degrees for the HadCRUT4 dataset, work out an equivalent for those who wish to use GISS and go from there.

  18. angech,
    I don’t actually get what you’re suggesting.

  19. angech says:

    Just that a baseline is needed, to use the anomalies, and a starting date and all we have to do is pick one and agree on it.
    Since there are multiple data sets one should be chosen as the reference standard for the IPCC and everyone else.
    What Richard Betts said.

  20. angech,

    Just that a baseline is needed, to use the anomalies, and a starting date and all we have to do is pick one and agree on it.

    In some sense, yes, and that it sort of what I think Hawkins et al. are suggesting.

    Since there are multiple data sets one should be chosen as the reference standard for the IPCC and everyone else.

    I don’t really agree with this. I think having multiple datasets is useful, since you can compare them to see if you get a consistent result.

  21. JCH says:

    OT: On Zhou and low clouds in the Eastern Pacific and all that, the paper has received its first cite:

    Observational evidence against strongly stabilizing tropical cloud feedbacks – Ian T. Williams and Ray T. Pierrehumbert

    Supporting Information for “Observational evidence against strongly stabilizing tropical cloud feedbacks”

  22. Andrew J Dodds says:

    I pick the Late Cretaceous Super Greenhouse. Before those uppity mammals started messing things up. Plus, no one is going to quibble about a ‘catastrophic’ tag, and most of the states that voted Trump/constituencies that voted Tory get obliterated. Result!

  23. Magma says:

    “Before those uppity mammals started messing things up.”

    Back when they were fuzzy little hors d’oeuvres for their saurian overlords.

  24. Eli Rabett says:

    Let Eli be the bunny in the manger here. From the standpoint of policy a firm baseline is idiotic. What is important are actions that move emissions to zero. This is COMPLETELY INDEPENDENT of the global temperature baseline. Defining a firm baseline will only be used to argue for the lay back and enjoy it school of policy. Arguing about whether the 3B (Better Betts Baseline) or the NOB (Nordhaus Original Baseline) should be used is a waste of time and an invitation to spending a couple of semesters in the Tol School of Statistical Abuse.

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