Implausible?

There was a recent paper looking at the near term acceleration in the rate of temperature change. The Guardian covered it in an article called global warming set to speed up to rates not seen for 1000 years, while Carbon brief has a slightly more nuanced Earth entering a new era of rapid temperature change, study warms.

Credit : Smith et al. (2015)

Credit : Smith et al. (2015)


The paper basically used results from climate models to determine how multi-decade rates of change would vary in the future under various emission pathways. The figure on the right shows the results for RCP4.5 and indicates that, globally, the 40-year trend by 2020 could be around 0.25 ± 0.05oC per decade. It also shows the trends for different regions, although quite why it doesn’t show Africa is a little confusing since it seems to show all the other regions. Richard Betts, however, has a Climate Lab Book post where he points out that this study didn’t take into account that recent warming has been slower than the longer-term trend. Richard concludes that it is more likely that by 2020, the 40-year trend would be between 0.14 and 0.18oC per decade.

I initially thought that Richard’s result was on the low side, but I suspect he’s about right. In 2020, the 40-year trend will be based on the period 1980-2020. If you use the Skeptical Science Trend calculator and choose the dataset that will give your the highest trend from 1980-now (HadCRUT4-hydbrid), you get a trend of 0.176 ± 0.048oC per decade. For the 40-year trend in 2020 to be 0.18oC per decade would (if I’ve done this right) require about 0.1oC of warming between now and 2020. Even that would be more than twice as fast as we’ve been warming over the last 10-15 years. No warming at all would give a trend of 0.15oC per decade. To get to 0.2oC per decade would require almost 0.2oC of warming between now and 2020, and 0.25oC per decade would require almost 0.4oC of warming in the next 5 years.

So, it seems quite unlikely that we could have enough warming in the next 5 years for the 40-year trend to exceed 0.2oC per decade. It’s possible, I guess, but seems unlikely. To be clear, though, if we continue to increase our emissions, warming will have to accelerate at some stage: we can’t continue to build up an ever increasing planetary energy imbalance without this happening eventually. The current slowdown will probably simply delay when we reach the higher trends suggested by Smith et al. (2015) – assuming, of course, that we continue to follow a high-emission pathway. Of course, I suspect that this is one of those papers that we’ll never hear the end of if/when the 40-year warming trend doesn’t exceed 0.2oC per decade by 2020. That numerous people have pointed out that it might be unlikely to reach those levels quite as soon as 2020, won’t stop the whiners from saying “but you said…..”.

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46 Responses to Implausible?

  1. Hyperactive Hydrologist says:

    Would you not use the 2000-2040 period to calculate the 2020 trend?

  2. Would you not use the 2000-2040 period to calculate the 2020 trend?

    In some cases, yes, but I don’t think it is what they did in this paper. I think that they defined it as the 40-year period ending in 2020, not the 40-year period ending in 2040. What they actually say is

    the rate of global-mean temperature increase in the CMIP5 (ref. 3) archive over 40-year periods increases to 0.25 ± 0.05 °C (1σ) per decade by 2020

  3. BBD says:

    Just wait until we start phasing coal out in earnest. Then we get to reap the Faustian Bargain Hansen et al. (2013).

  4. BBD,
    Indeed, I was also thinking about that. RCP2.6, for example, has – I think – faster near-term warming than some of the higher emission pathways, for that very reason.

    I’ve also just realised that the uncertainties in Smith et al. are 1σ not 2σ, so their work does suggest a higher probability of the trend being under 0.2oC per decade than I had initially thought.

  5. BBD says:

    Well that killed the conversation stone dead. Let’s talk about this photo I’ve just seen of a mad physicist diving into ice-bobbing, penguin-infested Antarctic waters so cold that they don’t even splash properly…

    😉

  6. Except, Rachel’s not pleased that I diminished her own cold water adventures 😀

  7. Rachel M says:

    Yeah, not happy Jan. There I was feeling proud of myself for swimming in the North Sea near Aberdeen in March and you have to trump me with ice and penguins. Ice and penguins … pftt

  8. Good thing I watched that youtube clip, because I was about to point out that it’s not Jan, it’s Mar.

  9. Rachel M says:

    It’s an Australianism to say “not happy Jan” and so I thought I’d better link to that since most people here aren’t Australian.

    But you’re still not invited to my birthday party.

  10. verytallguy says:

    I lived 200 metres from the North Sea for the first 18 years of my life. There’s a good reason penguins don’t live there. It’s too f*cking cold for them. The Antarctic is balmy by comparison.

  11. Rachel M says:

    You can come to my party, VTG 🙂

  12. BBD says:

    Don’t worry, Rachel, it’s a con trick. ATTP isn’t as ‘ard as he would have you believe. The upwelling Antarctic deep water is warm. The penguins in the photo were probably parboiled and dead in the water.

  13. Rachel M says:

    BBD, 😘

    Now that I look a second time, those penguins could very well be dead for all we know 😉

  14. Well, they all jumped out of the water after we jumped in, so they were either alive or animatronic.

  15. Rachel M says:

    So you say. But where’s the evidence?

  16. BBD says:

    On a more serious note, Richard Betts’ view on the likely evolution of the 40yr trend is persuasive, but it seems improbable that there will not be a resumption of rapid warming (~0.2C/decade or even higher) by mid-century. Increasing forcing (GHG and reduced anthro aerosols) and a shift in natural variability reducing OHU and deep water upwelling should do the trick. And then there’s the troubling methane eruptions up North.

    But of course this is simply alarmist.

  17. BBD says:

    Rachel

    The penguins look moribund to me. And as you were quick to note, ATTP has retreated into argument from assertion.

  18. I guess I can’t prove it isn’t just skillful taxidermy, but it looks pretty alive to me 🙂

  19. dhogaza says:

    Rachael M:

    “Now that I look a second time, those penguins could very well be dead for all we know”

    They probably are, if nothing else of old age. Looks like a long long time ago. The one he just posted looks like … film!

  20. dhogaza,

    They probably are, if nothing else of old age. Looks like a long long time ago. The one he just posted looks like … film!

    Even worse…slides!

  21. BBD says:

    Oh c’mon, ATTP. Totally different shot. Bird not in water. Remember that you are dealing with the Boogie Board Diva here. You can’t fool me.

    😉

  22. Bird not in water.

    I told you they all jumped out 😉

  23. BBD says:

    Who can blame them?

  24. John Hartz says:

    Speaking of the issue covered in the OP…

    There had never been as hot a 12-month period in NASA’s database as February 2014–January 2015. But that turned out to be a very short-lived record.

    NASA reported this weekend that last month was the second-hottest February on record, which now makes March 2014–February 2015 the hottest 12 months on record. This is using a 12-month moving average, so we can “see the march of temperature change over time,” rather than just once every calendar year.

    NASA: Earth Tops Hottest 12 Months On Record Again, Thanks To Warm February by Joe Romm, Thnk Progress, Mar 15, 2015

  25. Joshua says:

    Looks like after running amok over at Judith’s, Springer’s trying to mess up this blog also.

    Always classy, that Springer.

  26. BBD says:

    Joshua

    It’s me being silly, not DS.

    BBD

  27. JCH says:

    2014’s 12-month mean is now .673C (GISS adjusted). The 12-month mean ended on February 28, 2015 is .709C. So it went up .036C in 59 days. How many days it it until July 31, the next month when 2015 leave 2014 in the dust.

  28. BBD says:

    Exculpatory narrative: I was thinking of selkies.

    Now back to serious sh*t.

  29. David Springer says:

    Joshua says:
    March 16, 2015 at 12:31 am
    Looks like after running amok over at Judith’s, Springer’s trying to mess up this blog also.

    Always classy, that Springer.

    BBD says:
    March 16, 2015 at 12:43 am
    Joshua

    It’s me being silly, not DS.

    Do you make a habit of blaming others without evidence, Joshua? That your idea of classy?

    Thanks BBD.

  30. russellseitz says:

    “Richard Betts’ view on the likely evolution of the 40yr trend is persuasive

    The again, so was Hansen’s 40 years ago.

    Who wants to bet on decadal delta T’s of one tenth the IPCC year 2100 range starting in 2020

    Or 2030, 0r 40, or 50 …. ?

  31. Rachel M says:

    BBD,

    Who can blame them?

    I don’t remember AT having teeth as big as those but he did say it was a long time ago.

  32. I sort of fear the following scenario being played out (and such papers as this one by Smith et al. (2015) I sort of fear could end up being part of it):

    Suppose that the slowdown since around 2000 continues for an extra period long enough to influence modelers to agree with those who say that the models are running too hot, and then they cool down the models. But suppose that after that, an up to 60 year cyclic or quasi-cyclic internal variability of atmosphere-oceans interaction is finally confirmed via a confirmation of, say, a mechanism along the line of that proposed by Chen and Tung (2014), which in turn influences the modelers to realize that their models were not running too hot before and so they heat their models back up again. And this back and forth by mainstream climate science influences the general public to reject this re-heating of the models, those who reject mainstream climate science win enough of a victory, and then the world sees a high enough emissions path over a long enough period of time so that in roughly one or two centuries the world ecology and human civilization experiences catastrophe by heating the world to a degree close enough to even just the minimum degree examined by Sherwood and Huber (2010). All because present day mainstream climate science did not take seriously enough the possibility of an up to 60 year cyclic or quasi-cyclic internal variability of enough strength to make it look like the models are running too hot during a very crucial time when they’re not running too hot at all.

    (Before I go on, to anticipate a possible objection: No, I do not agree that it’s best to assume that a hypothesis is false and to hold that position until enough evidence is obtained to warrant moving away from that assumption. An example of this would be to assume the claims of Chen and Tung false until confirmed otherwise. I think the best starting point is to assume both that it’s possible that it’s true and that it’s possible that it’s false and to hold that position until enough evidence is obtained to warrant moving away from that assumption. With this latter position, we can do all kinds of conditional studies that assume the truth or falsity of the hypothesis to examine what the implications of its truth or falsity are. Mathematics, for instance, is loaded with such research, where, for instance, what we prove is what a presently unproved conjecture implies.)

    It seems to me that the recent papers by Marotzke and Forster (2015) and by Steinman Mann, and Miller (2015) are examples of what I mentioned parenthetically in that they seem to take seriously enough the possibility that there is strong enough atmosphere-oceans interaction giving up to 60 year cyclic or quasi-cyclic internal variability to examine its implications, the former doing so with its 62 year runs and the latter doing so by explicitly taking into account (and properly interpreting) the multi-decadal AMO and PDO (Curry and company I think wrongly interpret the AMO).

    The results of these two papers seem to be that the implications of such internal variability with cycles or quasi-cycles of such long periods of time are that the models are certainly *not* running too hot. And this, in my view, is why the community that rejects mainstream climate science is so keen on denigrating these papers.

  33. JCH says:

    this is why I do not believe in 60-year patterns in the modern SAT

    The PDO is due to flip positive. It can take as little ten years for it to peak. It has been on a downward trend since 1090 – 1985. That appears to have ended in 2012. That’s ~ 27- 32 years. Maybe the next 10 to 15 years will be positive PDO, and maybe the GMT will sky rocket.

  34. JCH says:

    1980 – 1985

  35. JCH says:

    Also, I thought Joshua was referring to the first commenter: Hyperactive Hydrologist.

  36. Rachel M says:

    The silly comments on this thread won’t make any sense unless you read the comments here – https://andthentheresphysics.wordpress.com/2014/08/13/some-kudos/#comment-50611. And yes, that is indeed a picture of AT in nothing but a pair of budgie smugglers in the Antarctic with living penguins in the background!! Or so he says ….

  37. Joshua says:

    Guilty as charged, Springer. Apologies for assuming that because you went crazy over the course of weeks with sock-puppets at Judith’s, culminating in yesterday’s non-stop spamming, including posting at Judith’s under Anders’ screenname, the concurrent weirdness/sock-puppetry here was done by you.

  38. BBD says:

    Sock-puppetry? Me posting as me?

    😉

  39. Joshua says:

    As i recall, there was a long list of “recent comments” that were by only one author (crowding out any other comments by other authors) whose name was they title of a post. Clicking on the link to the comment just brought me to the home page of the blog

  40. BBD says:

    There’s only one Boogie Board Diva on this blog, Joshua, and never you forget it!

    🙂

  41. R Graf says:

    JCH, You should read Clive Best’s post a few days ago on PDO here: http://clivebest.com/blog/?p=6418

    His plot shows PDO peaking in 1945, 2005 and due to bottom in about 2025-2030.

  42. BBD

    It’s worth noting the final paragraph of my Climate Lab Book post:

    The wider point made by Smith et al still stands – there is a clear risk of rates of climate change exceeding those in recent centuries, especially if greenhouse gas emissions continue to increase. Recent 40-year warming has already been unusual in the context of the last millennium, but possibly not completely unprecedented. However, our brief analysis here suggests that the recent hiatus may have put off the time at which 40-year warming exceeds that seen in the last millennium. Nevertheless, this may still happen within the next two decades. As Smith et al discuss, a key factor will be the transient climate response.

    Also, as I said in response to a question from David Rose, I don’t view this as particularly affecting my 2010 estimate of the earliest time at which global warming could reach 4C relative to pre-industrial (the 2060s, if emissions follow the high scenario, climate sensitivity is high and carbon cycle feedbacks are strong). So far I view this as just a constraint on the near-term projections – there’s too many other uncertainties affecting the longer term projections to allow any revised estimate of those.

  43. BBD says:

    Thanks Richard. As I said earlier, in amongst the silly bits, I think what you say is very reasonable.

  44. R Graf,
    I think Clive Best’s analysis is wrong. As I understand it, he’s assumed that the only external forcing is CO2 and hence that the forced temperature response is monotonically increasing. He, therefore, assumes that any variability about this is internal variability, when – in fact – some of this supposed variability is externally forced. So, Clive is over-estimating the internal contribution.

  45. Pingback: A juvenile tactic? | …and Then There's Physics

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