Stronger regional differences due to large-scale atmospheric flow.

I think there were some surprising aspects in Deser et al.‘s results. Not that I didn’t expect natural multi-annual variations to be unimportant (on shorter time scales, they are very pronounced), but what strikes me is the strong contrast (on a 50-year time scale) between the global mean temperature (lower graph), which was not very sensitive to the regional atmospheric circulation, and the regional temperatures which were strongly influenced.

It has long been recognized that local and regional climate would warm at different rates than the global mean, but not with such large differences as presented by Deser et al. at the time scales of 50 years and for continental scales. Their results imply that while some regions could experience almost zero warming over 50 years, this will be compensated by substantially stronger in other regions (because they also find that the global mean temperatures to be largely insensitive to the different model initial conditions).

These results also imply a surprisingly long persistence of weather regimes in different parts of the world. Usually, one tends to associate these with inter-annual to decadal scales. However, Deser et al observe:

Such intrinsic climate fluctuations occur not only on interannual-to-decadal timescales but also over periods as long as 50 years… even trends over 50 years are subject to considerable uncertainty owing to natural variability.

These findings were in particular important for the winter season at mid-to-high latitudes. Hence, they could be entirely attributed to chaotic dynamics. On the other hand, the two simulations that they highlighted in their study represented extreme cases, and most of the simulations suggested that the future outcome may be somewhere in between.

My interpretation of Deser et al.‘s results is that the range of possible future temperatures gets broader at the same time as the most likely outcome follows a warming curve. This means that the most likely scenario is warming for the future while there still is a small possibility that the temperature for a particular location hardly changes (or even cools) over a 50-year period.

If each simulation is equally likely and the distribution of results given by the ensemble of runs gives an indication of likelihood, then the most likely outcome is described by the value that most of the ensemble members cluster around.

Another way to look at this is that the signal-to-noise ratio doesn’t increase much over time, which makes some of the take-home messages from Brown & Wilby (2012) important to heed. They argue that downscaling for the future involves too many unknowns, but can nevertheless provide tentative input to a more comprehensive risk assessment based on many factors, all of which may not necessarily be related to climate.

The Deser et al. paper also sends a message to people who study regional climate change based on a small selection of climate models (i.e. only from their own country). There is a need to include the maximum amount of reliable information about the local climate, and that would include the range of possibilities and the probabilities associated with these.

It is of course possible that the climate model used by Deser et al. exaggerates the variability in the large-scale atmospheric flow. However, their findings may also potentially explain the observation that led Oldenborgh et al. (2009) to conclude that Europe has warmed faster than projected by the climate models.

p.s. The ENSEMBLES project did involve a “grand ensemble” (climateprediction.net); however, this has so far not been used extensively for describing local and regional climate. The grand ensemble has been more appropriate for describing the global mean state and large-scale phenomena (link to experiments).

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References

  1. C. Brown, and R.L. Wilby, "An alternate approach to assessing climate risks", Eos, Transactions American Geophysical Union, vol. 93, pp. 401-402, 2012. http://dx.doi.org/10.1029/2012EO410001
  2. G.J. van Oldenborgh, S. Drijfhout, A. van Ulden, R. Haarsma, A. Sterl, C. Severijns, W. Hazeleger, and H. Dijkstra, "Western Europe is warming much faster than expected", Climate of the Past, vol. 5, pp. 1-12, 2009. http://dx.doi.org/10.5194/cp-5-1-2009

59 comments on this post.
  1. Dave Person:

    Hi Tamino and Hank,

    Thank you for your replies. Tamino, you are correct that kriging can provide a better method to weight temperatures spatially provided there are sufficient observations with which to estimate the variogram particularly if there are discontinuities in the spatial variance-covariance structure. I do not know how many data points Berkeley had available for Alaska but it has to be many to interpolate temperature for such a large state or it is unlikely to offer much improvement. The interesting data on the UAF GI site are the temperature records for each of the stations. They show that warming trends vary considerably throughout the state with the greatest change happening on the North Slope (not surprising). Some correlate well with the putative “phase shift” of the PDO in 1976 and again in about 2005. The PDO cannot be a cause of long-term temperature change. It only (as I understand the index) indicates changes in how heat is distributed and as such contributes to local variation, which is what Deser et al. addressed. Currently, we seem to be in a negative PDO phase, which likely is contributing to a string of hard winters in SE Alaska despite a long-term warming trend. An interesting side note is that Eaglecrest ski area in Juneau was in serious financial trouble from lack of snow during the early part of last decade. Now they are doing well.

    Hank, I agree with you on Wendler’s statement about expecting a linear relation between temperature and CO2. To me, his analysis is naive at best and using r-squared to proportion relative effects is particularly egregious. At the very least, there are much better statistical methods for model selection such as Akaike information criteria (AIC). With respect to your question about who is arguing that warming reduces the need to protect winter range for deer, the answer is many of the U. S. Forest Service planners and foresters working on proposed timber sales within the Tongass National Forest. They are part of an agency that is in serious decline, budget-wise, mission-wise, and staffing-wise. Since WW2, they have been wedded to harvesting timber as their main mission and important funding support. That mission largely is over and the Tongass is one of the last places with timber resources available for harvest at an industrial scale despite the fact that it is heavily subsidized by the taxpayer. Hence, they are doing anything they can to keep that dead horse going.

    dave

  2. Dan H.:

    Thanks for you input Dave. I know many here do not like to hear about the influence of the PDO, but I do, and appreciate your insight. One question, based on the negative turn of the PDO, would you expect Alaskan temperatures to remain at their current levels or decrease (even slightly) in the coming decades?

  3. Hank Roberts:

    > expecting a linear relation between temperature and CO2

    Interviewed by Ken Rudin on National Public Radio this morning, Ralph Reed gave that as his reason believing there’s not a connection.

  4. Hank Roberts:

    http://pubs.acs.org/doi/abs/10.1021/es2044008

    Minding Our Methods: How Choice of Time Series, Reference Dates, and Statistical Approach Can Influence the Representation of Temperature Change

    “What may seem to be simple or arbitrary choices in these matters could potentially infuse significant bias into the interpretation of data, thereby distorting the representation of climate variability in Alaska and handicapping potential strategies for response. In this paper we demonstrate and emphasize how the use of different time scales, reference dates, and statistical approaches can generate highly disparate results, suggesting that careful use of these tools is critical for correctly interpreting and reporting climatic trends in Alaska and other polar regions.”

  5. Hank Roberts:

    and this illustrates the Minding Our Methods abstract:
    http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2012/esthag.2012.46.issue-14/es2044008/production/images/medium/es-2011-044008_0004.gif

  6. Dave Person:

    Hi Dan H,
    I expect Alaska and my part of SE Alaska to generally warm over the next few decades. I expect a negative PDO to mute that warming somewhat and a positive PDO to enhance it. However, my main concern in the short-term is if ocean processes like the PDO and ENSO interact with general warming to increase the risks of extreme cold and snowy periods and extreme warm periods which will play havoc with ecological communities.

    dave

  7. David B. Benson:

    More Intense North Atlantic Tropical Storms Likely in the Future
    http://www.sciencedaily.com/releases/2012/11/121130151651.htm
    is, I suppose, a ‘stronger regional difference’ but I would have posted this on an Unforced Variations thread if one had been open.

  8. Elle:

    Global Warming is indeed a phenomenon we can’t runaway from. I found motleygreen.com and was able to see that there are acts I can do to save the environment.

  9. Hank Roberts:

    > motleygreen
    I wonder who owns that site, widely spammed on blogs lately. It offers a 3-minute cancer cure: … motleygreen.com/beta/article-details-cure-cancer-using-your-own-technology-of-emotions-74
    Beware or be amused: claims a thinkwrap license; looking at their web page signifies accepting their terms of service; privacy policy is “you consent” to whatever they want. Yeek.