Tuesday, May 25, 2010

What a difference four months makes!

Deep Climate, at Tamino's, noted one of the interesting talks at the ICCC meeting was by Chip Knappenberger. It foreshadows a paper submitted to GRL by an eclectic group of authors:
“Assessing the consistency between short-term global temperature trends in observations and climate model projections"
by Patrick Michaels, John Christy, Chad Herman, Lucia Liljegren and James Annan

I presume Chip is an author too, although it isn't entirely clear. Anyway, he shows some plots, apparently from the paper, of temperature trends measured back from present to periods of from five to fifteen years. These are compared with model predictions, with the general idea of suggesting that they have been overpredicting warming. In fact, the talk pauses a couple of times to examine the phrase, written in very large font:

"Global Warming has Stopped!”

Global warming has stopped (or at least greatly slowed) and this is fast becoming a problem.

Present for this paper means end 2009. So I thought it might be interesting to update with four months more data.
(Updated discussion below)

Here are the two relevant slides from the talk. They split into land instrumental and satellite:

And here are my updates, moving the starting point forward four months. I haven't seriously tried to calculate the probability bounds - they just roughly follow the original for visual comparison.

Following Carrot Eater's suggestion, the plot is animated, with the higher value using the more recent data


Update: 
The new data shows that:
1. GISS trend is positive in the range
2. Hadcrut3 is weakly positive
3. NCDC is mixed
4. UAH is quite positive
5. RSS is mixed
Not really a basis for concluding that warming has stopped. And after a few more months of warmth....?

Looking forward

To see what the plots might look like by end 2010 (when this paper might appear), I calculated the same trend diagram assuming that each coming month, for each index, was as warm as April 2010. Here are the plots, with the old trends shown as thinner curves:

As you'll see, not only are all trend curves decidedly positive (warming) but getting close to the central value of the models.

16 comments:

  1. Interestingly enough, I'm starting to suspect that the main reason why GISTemp shows a higher trend over this particular period is its choice of SST series (e.g. HadSST1/Reynolds instead of HadSST2), since the former has a decidedly lower '98 ENSO and immediately post-ENSO temps but catches up later in the decade:

    http://i81.photobucket.com/albums/j237/hausfath/Picture406.png

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  2. There is a step change in HadSST2 in 1998 coinciding with new buoy data. It is almost certainly an artifact. Since then, HadSST2 drifts downward.

    HadISST and Reynolds are very close for their period of overlap. In earlier decades, HadISST is a lot less variable than HadSST2 (much less divergence ~1910 and ~1940), which I presume has to do with the extensive homogenization it has undergone.

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  3. Nick: slightly OT, but I don't suppose you could produce a version of ERSSTv3 from http://www.ncdc.noaa.gov/oa/climate/research/sst/ersstv3.php#grid in the form of the HadSST2 data we were using earlier (e.g. 5x5 gridded, one year per row).

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  4. Zeke,
    Yes, I'll try. At the moment I only see 2x2 monthly data there - is there actually 5x5?

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  5. Looks like there is only 2x2. That should work as well; I'll just have to badger Chad into uploading a 2x2 land mask.

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  6. if there were ever a plot that was begging to be animated, this is it. Animate through different endpoints. The tail on the left would probably wag quite a bit, as you are getting at by forwarding the end date by 4 months.

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  7. CE, yes, good idea ( a new trick for me). As you'll see I've added a couple of (static) speculative plots.

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  8. I see that. I hope the authors don't make too much of the particular positioning of their curves at that snapshot in time.

    and yes, I've never animated a plot before either. But in this case, it will get busy if you overlay too many static traces on the same plot, and unwieldy if you show too many static plots.. maybe a GISS-only plot, and a CRU-only plot, etc, with each having multiple data series for varying endpoints, would do the trick.

    Where is all this coming from, anyway? I don't see the paper up on the GRL website yet.

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  9. CE, as you'll I did get the plot animated - it's very easy with gif's and Imagemagick.

    The only info about the paper at the moment comes from Chip's ICCC talk. It's not clear if it's been accepted at GRL. James Annan says a little about it here

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  10. Thanks for this post, Nick (and the updates).

    For your "looking forward" update, you assume May-Dec 2010 will have the same temperature as April 2010.

    I've looked a bit at the aftermath of past El Nino episodes, and at the relationship between temperatures and the NINO3.4 index during the previous X months. It's a very noisy signal, but on average I think we would expect the May-Dec 2010 average temp to be slightly lower than the April temp (say, 0.05 to 0.1C lower).

    So while the trend will almost certainly be even closer to the models than it is now, it might be a bit lower than what you show in your "looking forward" graphs.

    Or ... not. We'll see!

    Anyway, thanks again for doing all this work.

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  11. cce: "There is a step change in HadSST2 in 1998 coinciding with new buoy. It is almost certainly an artifact."

    This is a lot less obvious than you think.

    The step change was started around 2001, not 1998 and it's by no means not the only step change in SST.

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  12. Relative to Reynolds OIv2 and HadISST, there is a ~0.1 degree upward step change in HadSST2 beginning in 1998 (not 2001). The step coincides with HadSST2's transition from ICOADS to NCEP-GTS (which is to be discontinued at the end of this year).

    Tisdale talks about this step on occasion, eg:
    http://bobtisdale.blogspot.com/2009/12/met-office-prediction-climate-could.html

    It's obviously not the only step change, but it is the only one relevent to Zeke's comment.

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  13. To update my initial comment, I got my hands on a run of GISTemp using the Hadley area only. Looks like arctic interpolation and different SST series split the blame fairly evenly.

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  14. CCE "Relative to Reynolds OIv2 and HadISST, there is a ~0.1 degree upward step change in HadSST2 beginning in 1998 (not 2001).

    A picture is worth 10^10^10 words.

    1998 is the ENSO event. It resembles a impulse with a decaying response, not a step function.

    If there is a step, it shows up in 2001, not 1998. . (There's roughly a 0.2°C discontinuity at the start of 2001.)

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  15. Carrick,

    I am not talking about a step change in actual SST since 2001. I am talking about an artificial step change in HadSST2 since 1998.

    GISTEMP uses the Reynolds OIv2 satellite SST since late 1981, and HadISST before that (the "I" in HadISST is important). HadCRUT uses HadSST2. HadSST2 switches to NCEP-GTS data in 1998. The difference between Reynolds OIv2 and HadSST2 is plotted here:

    http://i47.tinypic.com/2gx2nwm.png

    There is a clear step change beginning in 1998, not 2001, which elevates HadCRUT's temperatures relative to GISTEMP.

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  16. Thanks for the explanation CCE. I'll buy that.

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