Sunday, January 27, 2019

How about changing and clarifying IPCC targets for global mean temperature

Sou | 5:25 PM Go to the first of 12 comments. Add a comment
The aim is to limit global warming to 1.5 C above pre-industrial temperatures; however, there has long been some contention and confusion around what is meant by the targets of 1.5 C and 2 C.

I don't know that anyone will ever agree on what pre-industrial means exactly, which gives a lot of room for inept leaders to wriggle out of their obligations. That's why I'm suggesting the IPCC and its member countries set and agree on targets where the meaning is clear, tangible, more precise, and to which people can relate more readily.

My idea is to change the simple message of 1.5 C or 2 C above pre-industrial to 1 C or 1.5 C above the 1951-1980 mean.

Target: Limit to 1 degree of warming (above the 1951-1980 mean)

Here's a chart showing GISTemp and HadCRUT, with the current pre-industrial targets superimposed, assuming the pre-industrial baseline is around 0.3C below the temperatures at the turn of the century. This would make them 0.5C below the 1951-1980 mean.

If the temperature around 1900 was 0.3 C above the pre-industrial mean, then the new targets could be 1 degree C and 1.5 degrees C above the 1951-1980 mean. That's not so hard, though it's horrible that we're already touching the target. It won't be long before we've missed the first one and are barreling toward the limit. (Note: in the chart, 2018 only includes monthly temperatures to November 2018.)

The merits of 1 degree

Seems to me that setting new targets in terms of an increase above mid 20th century temperatures has many merits.
  • It means only one number is needed, the 1951-1980 mean. People don't have to do calculations using pre-industrial numbers that are iffy in the first place and try to set them against current averages.
  • The data for the 20th century is freely available to all and leaves little room for misinterpretation, unlike "pre-industrial".
  • Many people alive today still remember what the weather was like in the period from 1951 to 1980. In the future, provided civilisation survives, there will be lots of reliable records available from the period.
  • The 30 years from 1951-1980 is not so different to the average of the twentieth century.
  • 1951-1980 was a relatively flat period in terms of temperature deviation (although this may be in part because of the odd spike during WWII, which might not reflect reality).
  • The period is used by NASA, and it's not that hard to adjust other datasets to work out the difference.
The new targets would need to be consistent with an estimate of how much atmospheric carbon dioxide we can cope with and still have societies survive in the long run. That's a job for scientists.

Back last year, a number of scientists had a letter published in Nature, in which they discussed the inconsistencies in interpretation of the current targets and the impact of this. In closing, they wrote:
We therefore recommend that a clear definition of GMST change is agreed, so that mitigation actions required to limit climate change impacts are assessed using self-consistent information. This would prevent apparently contradictory results due to differing interpretations.
Schurer, A., Cowtan, K., Hawkins, E., Mann, M.E., Scott, V., Tett, S.F.B., Interpreting the Paris Climate Target, Nature Geoscience, 1752-0908, doi:10.1038/s41561-018-0086-8, 2018.

Change the message, for clarity in the longer term

I suggest changing the messaging to make it clearer. That is, instead of setting a target against the vagueness of pre-industrial, set it against the average of the 1951-1980 global mean.

Keep in mind that it's important this message lasts for decades (at least) and is as meaningful in 2080 as it is today. (By 2080 the 39-year-olds born in 1980 will be turning 100 years of age.) It could be set against the WMO's 1961-1980 mean or even against the twentieth century mean. The 1951-1980 might be the best of these, though.

Whatever - I'm all for simple messaging. It works with the general public. The longer it's put off, the harder it will be and the more disagreement and indecision it will cause.

Do it now. Think of the long term benefits not the short term discomfort. As is obvious, it's not that hard to get a new message out these days, especially if you have a good social media manager with a strong stable of ambassadors and influencers, a PR company, willing journos, and the backing of climate experts and world leaders.

As a final note, it's been pointed out to me that there is a lot more to climate change than the annual ups and downs in global temperature. On the other hand, temperature is something people relate to very easily. If they want to explore more they can then look at rainfall, drought, heatwaves, floods, bushfires, sea level rise, melting ice and all the other changes that are happening.

Your thoughts?

What do you think? Is this a silly idea or a sensible move? I know there will be lots of arguments against (causing confusion, the smaller numbers aren't as scary etc.). On the other hand, IMO it would be short term pain for long term gain, or is that wishful thinking? Not that it would be easy to change something as entrenched as the IPCC (or the UN).

An alternative (added later)

There was one variation I'd thought about, but rejected because it required another calculation when using an instrumental dataset. However, after someone else suggested it I realise it's worth more consideration, particularly in the way it was expressed:
I'm warming to this idea and will use it in future "hottest ever" posts. I particularly like Dr Vermeer's analogy with BP, which makes it easier to explain to people :)

References and further reading

Schurer, A.P., Mann, M.E., Hawkins, E., Hegerl, G.C., Tett, S.F.B., Importance of the pre-Industrial baseline for likelihood of exceeding Paris goals, Nature Climate Change, 7, 563-567, 2017.

Schurer, A., Cowtan, K., Hawkins, E., Mann, M.E., Scott, V., Tett, S.F.B., Interpreting the Paris Climate Target, Nature Geoscience, 1752-0908, doi:10.1038/s41561-018-0086-8, 2018.

Global Warming of 1.5 ºC - Special Report from IPCC, 2018


  1. Is it a good idea? It depends on who it is for.

    For the scientists and policy builders it is a very good idea to standardise the base line so everyone is working from the same figures and within the same framework. Results and conclusions would be more directly comparable.

    For the general public it practically makes little difference. Though it might introduce some confusion and be viewed as scientists changing their mind again. Of course denierland would exploit any problems to promote the idea that the science is not settled, moving goalposts, tricks, hiding the decline blah blah blah ...

    1. Those are good points, Jammy. I'm now going to use the alternative I've added to the main post. That is, defining pre-industrial as the 1951-1980 mean minus 0.5 C. That keeps the current targets and gives me an easy way to compare now to the target. That is, until/unless scientists tell me the number (0.5 C) should be something else :)

      This shows we've almost hit the first target (1.5 C) already and at this rate will exceed it in just a few years. I'll need to check the trend lines, will do that in a future post.

    2. or just tell everyone the amount of warming left including ocean inertia before we hit the cutoff and what our chances are for each level 1.5C i would think would be already passed using that metric.. 2C about .5C to go with a 60% chance. just me

  2. Given the Homo Moronic is never going to meet any target my interest would be in predicting future targets that will also not be met and the dates at which those targets will become fashionable. How does the following scheme look?

    2030 +2.0C
    2050 +3.0C
    2060 +4.0C

    By about that last stage I'd expect any civilised discussion about targets to cease.

  3. It just feels like "arranging deckchairs on the Titanic" now. As Jammy Dodger says "blah blah blah"

  4. You people really don't see how futile all this is.... China commissions more new coal fired power stations every fortnight than our entire country has operating now.


    And to make matters worse... a lot of them are being fueled with Aussie coal. How good is that?

    You can set whatever arbitrary target you like... it won't change what's happening in the real world.

    1. So, what are the per capita emissions in China compared to the US?

  5. My impression a couple of years ago, using the BerkeleyEarth data, was that the first half of the 19th century was about 0.4 K lower than the mid-20th century mean. There are other reconstructions that show that the mean global temperature at the beginning of the Industrial Revolution (~1750) was about 0.1 K below the beginning of the 19th century. In my head I've always added this increment to any reference to the mid-20th century baseline in acknowledgement of the initial warming resulting from the early use of coal, and of large-scale deforestation for timber ships, housing, and agriculture.

    Looking through my bookmarks I found this, that reflects my thinking:


    I recall a couple of years ago when I and several others (BBD?) were noting a 1.2 K warming since pre-Industrial following a record annual global temperature and being shouted down somewhat for the interpolation, with 0.9-1.0 K being proffered as a more reasonable figure. Tamino's just posted on the 2018 global temperature (https://tamino.wordpress.com/2019/01/26/global-temperature-2018/) and it demonstrates a ~1.3 K smoothed increase since the 19th century, which kinda reinforces the 1.2 K value we were promoting a coulpe of years ago...

    The fundamentally frightening thing is that for all of our decades of talk we have no significant action on the ground*, and there is still still a ceaseless Mordoring of denialati orcs throwing themselves howling toward the science in a frenzy of rabid hate and vitriol, regardless of now often it skewers them - yes, 'Skeptikal' (sic), I'm including you in that...

    Anyway, the point is that I would go with Martin's suggestion as it provides a simple reference to the easily-used 20th century baseline, whilst also easily incorporating the full amount of warming realised by human carbon emissions over the last few hundred years. It's important to fix the baselines solidly because governments of all persuasions (especially the science-denying conservative Australian ones) are vigorously predisposed to continually shifting their reference periods forward when they develop new policies. We have to stop this, because we're running out of room to accomplish any worthwhile mitigation.

    I'm pretty sure that hindsight at the end of the 21st century will indicate that 1.2-1.3 K warming was where the Great Barrier Reef and the Tasmania kelp forests were effectively lost (amongst other ecosystems...): if we're not to lose large swaths of currently-habitable land and indeed the capacity to maintain a cohesive global civilisation, we need to be constantly and closely ensuring that we don't exceed the pre-Industrial baseline by more than 2 K, and if we want to preserve some of our current level of biodiversity, even less...

    Even then it will be ugly, but if we think for a moment that we can keep putting it off to the future, all that we're doing is wilfully denying the fact that with our current inaction we're signing the death warrants of our decendants and the global ecosystems in which they would have lived. If we want to pretend to being an advanced species we cannot continue down that path.

    *Exhibit 1: https://www.co2.earth/keeling-curve-monthly

  6. I agree, 1-1.5 degrees above 1951-1980 is a clearer message than 1.5-2 degrees above the elusive " preindustrial" (When, uncertain data, poor global coverage, etc...?)

    Another way to find the " preindustrial" temperatures is to extrapolate the function of temperature vs log CO2 back to a preindustrial level of CO2, e g 280 ppm.

    I did the following chart almost a year ago, but I don't think it will change much with 2018 included. The chart includes a "best fit" 14 years lag, to account for commited warming, but the lower end (-0.45 C at 280 ppm) is very robust and will only change by 0.01 C if the lag is set to zero.


    It looks like Gistemp loti will pass 1.5 C above preindustrial before 2030 (or 1.05 C above 1951-1980 avg).

    Another prediction is that climate sensitivity, the temperature when the atmospheric CO2-content is doubled, is around 3C, but I guess you have heard that before..

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  8. And in the latest news regarding denialist trashing of the planet, Trump appoints John Christie to the board of the EPA.


    That's like appointing Stephen Arroyo to run NASA.

  9. Sou,

    I think that the ideas that you have discussed in this article, make good sense.

    Pre-industrial is too vague, and leaves too much wriggle room.

    I prefer the target being above the 1951-1980 mean. It makes global warming a "recent" phenomenon. This stops arguments about the warming from 1910 to 1940 (was it natural, or caused by humans).

    There is a danger in setting the target too low. If people have little possibility of meeting the target, then they will ignore it.

    But you shouldn't listen to what I say. Because I am just a Denier.


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