Cowtan and Way global average temperature observations compared to CMIP5 models


It is well known that the Arctic is warming up much faster than the rest of the globe. As a consequence, datasets which omit this region (HadCRUT and NOAA) underestimate the global warming trend. A new paper by Cowtan and Way addresses this cool bias by using satellite data to fill in these data gaps. They make a good case that this method also improves upon the NASA GISS dataset, which uses extrapolated data from surface stations to partly fill in the data sparse regions. Combining their new method of infilling with the most up-to-date sea surface temperatures gives a substantially larger trend over the last 15 years than the abovementioned datasets do. The temporary slowdown in global surface warming (also dubbed “the pause”) nearly disappears. As Michael Tobis notes:

This demonstrates is how very un-robust the “slowdown” is.

The corrections don’t amount to a huge change in absolute temperature change, and the new data actually fall inside the uncertainty envelope provided by HadCRUT4. As the paper correctly states:

While short term trends are generally treated with a suitable level of caution by specialists in the field, they feature significantly in the public discourse on climate change.

In the figure below (made by Jos Hagelaars) the global average temperature as calculated by Cowtan and Way (“C&W hybrid”) is compared to both the HadCRUT4 dataset and the CMIP5 multi-model mean as well as its 5% and 95% percentile values (RCP8.5): [Update: The figure below has
been replaced, since the original was found to be in error during discussions on CA). The confidence interval of this corrected graph is substantially narrower than the erroneous original one. Note that the current graph shows the 5 to 95 percentile range of model runs (i.e. the 90% confidence interval), whereas the previous ones showed the 95% confidence interval. At the bottom of the post a similar figure with both confidence intervals as well as the two sigma range is shown.


Also with these data improvements, recent observations are at the low side of the CMIP5 model range. The comparison of observations to models has to be interpreted with caution however. Some people like to jump to preferred conclusions, but it’s good to keep in mind that the expected warming at a specific point in time depends on a combination of factors. Any of these factors -as well as shortcomings in the observational data, such as those discussed by Cowtan and Way- could contribute to a mismatch between observations and models:

– radiative forcing

– equilibrium climate sensitivity

– climate response time

– natural unforced variability

The last factor means that one shouldn’t expect the multi-model mean (in which most variability is cancelled out) to be identical to the observations (which are the result of a particular realisation of natural variability).

Cowtan and Way made a very clear video in which the main results of their paper are explained in just a few minutes. Highly recommended watching:

More commentary on the paper on e.g. RC (Rahmstorf), SkS (Cowtan and Way), Guardian (Nuccitelli), P3 (Tobis), Victor Venema, Neven. See also this very useful background information provided by the authors.

[some typos corrected and clarifications added, 16-11. Erroneous figure replaced 21-11.]

Update: Below a similar figure as above, with different confidence intervals for the model runs shown. 


Update 2 (Feb 2014):

Jos Hagelaars added Cowtan and Way’s data for 2013 to a figure comparing observations to model projections:

Jos Hagelaars - comparison_cmip5_hadcrut4_cowtanway_2013

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17 Responses to “Cowtan and Way global average temperature observations compared to CMIP5 models”

  1. NevenA Says:

    I’ve added your graph to my Arctic Sea Ice blog post on The ‘hiatus’ and the Arctic, Jos. Thanks a lot.

  2. Kevin C Says:

    Thanks for doing the model comparison. As we’ve noted the changes are pretty small, and the fact that they make a big difference to the trend just goes to highlight the fragility of short term trends.

    As to whether we can draw any conclusions from the model-observation difference, that question is certainly beyond my expertise.

  3. steve Says:

    It appears that temperatures were lowered for El Niño years, and raised for La Niña years.

  4. Kevin C Says:

    It’s a bit more subtle than that, as the thing which makes the difference is the temperature contrast between the observed and unobserved regions. Robert has written a bit about this in the FAQ:
    (click the more/less link under the short answer.)

  5. Ruth Dixon Says:

    I notice you don’t say that Steve McIntyre identified and diagnosed the error in the first graph in your post. You just say that the graph ‘was found to be in error during discussions at CA’.

    Anyway, you may choose not to publish this comment, but I wanted to say that I feel strongly that due acknowledgement should be given when appropriate. A link to a blog identified only by its initials does not seem to me to be proper acknowledgement.

  6. Marco Says:

    Ruth Dixon, there is a direct link(!) to the discussions at the appropriate place.

    If you are so concerned about proper acknowledgments, why don’t you ask Steve McIntyre to properly acknowledge Deepclimate for exposing his inappropriate selective quoting from the climategate e-mails, as e.g. shown here:
    You see, McIntyre DID make the correction, ultimately, acknowledging he had it wrong. But he did not acknowledge anyone at all, nor did he refer to the blog that showed him wrong.

  7. Ruth Dixon (@ruth_dixon) Says:

    Marco, I’m not sure why you are referring to a 2009 thread, but isn’t this an acknowledgement? “Thanks to Deep Climate for shedding additional insight into the chronology.”

  8. Marco Says:

    No, Ruth, it is not an acknowledgment; showing that someone had selectively quoted an e-mail and that the removed part completely contradicted the claim is not “additional insight”. McIntyre fails to acknowledge he was wrong.

    And why not refer to a 2009 thread?

  9. Paul Kelly Says:

    There’s quite a bit of pretty heady discussion at CA with Robert Way about his paper. At one point he said: “The question I have is if in the kriging process how much spatial autocorrelation is there in the solution (e.g. do residual weather patterns produce synoptics?)”. No one there had an answer. Does anyone here?

  10. Robert Way Says:

    Paul Kelly,
    That comment was to Steven Mosher regarding the Berkeley approach.

  11. Rob Dekker Says:

    Paul Kelly,

    On CA on this topic, I see a misleading graph by McIntyre followed by a below the belt smear against Robert Way, and one against Hansen, followed by countless comments with more smearing and “discussions” of the security breach of the SkS private forum, and if it can be considered a “hack” or not, lots of criticism about statistical methods used in Cowtan and Way 2013, but nobody presents anything better, and topped-off with the usual dosis of McIntyre admiration.

    But noone of these self-proclaimed “auditors” seems to be able to refute anything stated in Cowtan and Way 2013.

  12. Paul Kelly Says:

    Rob Dekker,

    Lookin’ for a fight, ay? Just Kidding. I only read about 5% of the comments at CA, so I missed some of what you saw. I did read all the comments there by RW and McI on the several threads on this topic. There were a few there where was an actual dialogue on the science that were very enjoyable.

    They also aired personal grievances that, as RW said, may be better dealt with off the internet. I got the impression that there were grounds for mutual respect but not friendship. Many of the other commenters I read were complimentary to RW for his participation and as a scientist. McI’s criticisms mostly involved proxy selection, rather than statistical methods. On one thread they discussed a supporting paper. RW seemed to agree, at least somewhat, with McI’s critique of it.

  13. Sean OConnor Says:

    Will this graph get updated with 2013 data?

  14. Bob Brand Says:

    Hi Sean OConnor,

    Jos Hagelaars has an up-to-date version of the graph posted here on the Dutch Klimaatverandering blog:

    This includes 2013.

  15. Bart Verheggen Says:

    I added the graph as an update to the post. Thanks for the pointer/reminder, Bob.

  16. Sean OConnor Says:


  17. john byatt Says:

    the deniers are are using all your pre corrected graphs . they have no shame, the url’s give it away

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