New paper on forcings of historical European temperatures

From Nature Geoscience

Influence of human and natural forcing on European seasonal temperatures

Gabriele Hegerl, Juerg Luterbacher, Fidel González-Rouco, Simon F. B. Tett, Thomas Crowley & Elena Xoplaki Journal name: Nature Geoscience DOI: doi:10.1038/ngeo1057

It is the regional and seasonal expression of climate change that determines the effect of greenhouse warming on ecosystems and society1. Whereas anthropogenic influences on European temperatures have been detected over the twentieth century2, 3, it has been suggested that the impact of external influences on European temperatures before 1900 is negligible4.

Here we use reconstructions of seasonal European land temperature5, 6 and simulations with three global climate models7, 8, 9 to show that external influences on climate—such as the concentrations of stratospheric volcanic aerosols or greenhouse gases, other anthropogenic effects and possibly changes in total solar irradiance—have had a discernible influence on European temperatures throughout the past five centuries. In particular, we find that external forcing contributes significantly (p<5%) to the reconstructed long-term variability of winter and spring temperatures and that it is responsible for a best guess of 75% of the observed winter warming since the late seventeenth century.

This warming is largely attributable to greenhouse-gas forcing. Summer temperatures show detectable (p<5%) interdecadal variations in response to external forcing before 1900 only. Finally, throughout the record we detect highly significant summer cooling and significant winter warming following volcanic eruptions.

See the:  Supplementary Information (995KB)

Excerpt:

Based on the multiregression result for European seasonal temperature described in the body of the paper, there is some evidence for solar forcing being detectable in summer, but the result was sensitive to the analysis period. However, our knowledge on forcing and response is not equally robust between forcings. For example, greenhouse gas

forcing is far better constrained than solar forcing, and volcanic forcing could be argued

to be more robust than solar as well (e.g. ref. 23).

To further investigate to what extent our results are robust to first identifying the more robust forcing responses, we used a stepwise regression, which first estimates the response to better constrained forcings, such as greenhouse gases and volcanism, and estimates solar forcing from the residual. To enhance power, we also use the spatial pattern.

This is equivalent to using a solar forcing fingerprint in time that is orthogonalized to that of anthropogenic forcing (see figure SI6; note that this essentially removes the anthropogenic component from the timeseries and resulting spatial pattern prior

to a regression on the solar timeseries).

This approach is consistent with the greater confidence in the shape and size of the anthropogenic forcing. Note that if data up to 1950 are used, the only difference between the orthogonal and original regressor is that the longterm trend is no longer visible (Figure SI6). The resulting regression pattern was compared with patterns obtained by regression of a random time series of the same autocorrelation as the solar response time series onto the reconstruction data (see figure SI6 for some examples).

If the summer reconstruction over the period 1500 to 1950 is used, then the response

pattern to solar forcing is significantly warmer in the area average than that obtained from random time series in the reconstruction. If the same is done to model data, then the result is warming, which is not significant, but its pattern (Figure SI7) projects more strongly on that from the reconstruction than 90% of the cases where a random timeseries was regressed on both models and reconstruction. Similar results are obtained if the timeseries is analyzed until 1996 rather than 1950. In contrast, using the shorter period back to 1675 provides insignificant results.

However, if the solar pattern is orthogonalized to both the anthropogenic and volcanic EBM fingerprints (effectively removing the contribution by both forcings to the reconstruction prior to analysis) the response pattern is no longer detectable. This raises concerns

that despite a low correlation between the EBM response to solar forcing and volcanism (0.11), some degeneracy may remain between both, particularly given that that both solar forcing and volcanism tend to cool the period termed the Little Ice Age. Thus, the detection of a solar response in European summer temperatures remains uncertain.

Regressions of the solar forcing timeseries on European temperatures in other seasons than summer (JJA) show no evidence for a detectable solar signal, and larger samples and model simulations with individual forcings are needed to assess the possibility of a dynamical response to solar forcing in the cold season as discussed in the literature.

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h/t to Dr. Leif Svalgaard

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30 thoughts on “New paper on forcings of historical European temperatures

  1. Jimbo,
    Unfortunately there are two versions of HadCRUT3, one by UEA/CRU and the other by the Met Office, obtained by different methods of averaging. I have always followed CRU’s, and this gives 2010 as only the 3rd equal warmest. A lousy 3rd, after being hyped as the warmest!
    The December monthly value has been published at the UEA website, 0.251 and the lowest monthly value since February 2008. This gives us:
    1998: 0.548
    2005: 0.482
    2003: 0.475
    2010: 0.475
    Rich.

  2. Sorry if this is of topic. Apologies.
    But have you seen the new headline on the BBC website (but not, curiously championed by news 24 or its teletext? Quaeritur) that ’2010 hits global temperature high’ (notice the lack of conviction in that?), the small print being ’2010 was the warmest year since global records began in 1850 – although margins of uncertainty make it a statistical tie with 1998 and 2005′. Strange. Does that mean there has been no change for a decade? Of course, there is the question of whether anyone can trust these figures, harbored as they are by the true believers.
    Apparently this is based on a new press release by the WMO. Voltaire: Écrasez l’Infâme

  3. Sorry I couldn’t get past this: “Whereas anthropogenic influences on European temperatures have been detected over the twentieth century”.

  4. This is an excellent example of, if you torture the data enough it will appear to give you what you want.

  5. As usual, you have to wonder about cause and effect.
    Would the ‘anthropogenic’ factors include something like deforestation? Isn’t it clear that human population growth correlates with warming? Wouldn’t factors like disease and crop yield that affect the human population be influenced by climate? For example, the French Revolution caused by famine due to cold weather. Or, perhaps plague made worse by rats with fleas looking for food and warmth. As the population grows, so do human activities. It seems reasonable that climate and human activites would be correlated. However, how do we separate climate and human activities in terms of cause and effect?

  6. Would have been a better paper, if they’d included AMO as a “forcing”. How can they ignore such a large source of variability/noise & still get published?

  7. The ‘robustness’ of this paper is very much surrounded by circumspection! That it is based on ‘modeling’ as against a supposed paleo record leaves everything in doubt. The only take home result is, perhaps, they concede what is obvious – solar irradience. Or perhaps my superficial reading is wrong?

  8. Obviously, globally, 2010 was a warm year. Given El Nino conditions this was to be expected. Whether it was the warmest, 2nd warmest, 3rd warmest year is not the issue. The real test will be 2012 and 2013.
    2011 will undoubtedly be a cooler year. Heck even the Mrt Office are saying that. The real issue is whether temperatures recover in 2012 & 13 as they did in 2000 & 01 following the 98 El Nino and 99 La Nina. If temperatures do not rebound in similar fashion then this will be the first noteworthy observation that we are likely in for a prolonged period of cooler temperatures. The cycular nature of warming/cooling trends will become more obvious. It will be at this point that explanations will be more necessary and more difficult to spin.
    Of course, we can always rely upon the BBC to put a different (and predictable) stance on such stories.

  9. This is great because they plotted HADCM3 out to 2100 (see main paper, fig s-12) with the instrument record terminated just before the recent downturn.
    http://hadobs.metoffice.com/hadcet/
    We can now watch the model fail as temperatures appear to be dropping or they can convince me by seeing temperatures increase and verifying the model. I am much more convinced by this paper:
    http://lch.web.psi.ch/files/Publikationen/analytic/Eichleretal_GRL2009.pdf
    that demonstrates a twenty year lag between solar forcing and temperature change. In other words aside from ghg forcing it predicts cooling to start in 2010. This is exactly what is happening. This paper claims that only 50% of the twentieth century temp change can be caused by solar but at the site where the ice core for the reconstruction was gathered the local temp increase is twice that of the global (polar amp?) increase.

  10. This paper, in my opinion, carefully avoids the Medieval warm period to make the current warm period look more startling. Therefore the following link will give you my favorite reconstruction for Greenland that includes archaeology and historical info and allow one to put the graph from the above paper in more of a historical perspective.
    http://en.wikipedia.org/wiki/File:Grtemp.png

  11. There’s something that doesn’t smell right about this paper apart from the model simulations. Just count how many times the word “robust” is used.

  12. @richard1225
    The paper doesn’t avoid the MCA. It employs reconstruction-data, that just isn’t available for that period.

  13. This is yet another proof that the Aardvarkian constant is masking an escalating Jim-Jam factor with alarming implications for the Snoozeledorph!

  14. It seems to me everything is A OK, just as it has always been,
    I would ask, if the planet is the warmest ever why has the worst US drought ever in the 30`s not been equaled. The three-year drought of the late 1980s (1987-1989) covered 36% of the United States at its peak. Compared to the Dust Bowl drought, which covered 70% during its worst year.
    http://www.ccccok.org/museum/dustbowl.html
    http://www.english.illinois.edu/maps/depression/dustbowl.htm
    http://www.ncdc.noaa.gov/paleo/drought/drght_history.html
    The biggest weather event of the 1930`s in the UK, this next link provides some superb historical news clips and photo`s.
    http://www.ukweatherworld.co.uk/forum/forums/thread-view.asp?tid=20590&posts=14
    Can you comprehend what the warmers would say if this happened today.
    As far as global temperatures are concerned, total garbage.

  15. ob says:
    January 20, 2011 at 11:41 am
    @richard1225
    The paper doesn’t avoid the MCA. It employs reconstruction-data, that just isn’t available for that period.
    ________________________
    Could you mean: ‘fake it ’til you make it’?

  16. ob says:
    January 20, 2011 at 11:41 am
    “@richard1225
    The paper doesn’t avoid the MCA. ”
    ob carefully avoids the term MWP… we don’t want to give the sheeple the impression it was WARM back then, right? Fine-tuned climate communication…

  17. “The simulation driven with all forcings combined is driven by prescribed changes in volcanic forcing, solar irradiance, orbital forcing, greenhouse gases, tropospheric sulphate aerosol, stratospheric ozone and land-use/land-cover (for details see ref 13). The simulation used here is downloaded from the SOAP project (http://www.cru.uea.ac.uk/cru/projects/soap/data/model/), and uses unrealistically large ozone forcing from 1970 on. However, the difference to a simulation where the last 3 decades have been rerun, using more realistic ozone forcing, is small for European seasonal mean temperatures, and consistent with internal variability. The corrected version is used for splicing with the future simulation for figure SI2. The HadCM3 simulation was extended to 2100 using the A2 scenario with greenhouse gas and other drivers14.”
    So the used the surface record and the proxy records, both highly questionable, which the models are already attuned to, and got the results the models must give, as that is how they are written. So yes, they match the past which their pal review friends created. They ignore ocean cycles as well as changes in cloud cover and they self support. What I wish to see is this “The HadCM3 simulation was extended to 2100 using the A2 scenario with greenhouse gas and other drivers14.”
    Of course it is a projection, not a prediction.

  18. richard verney,
    The real question is, does this actually mean anything: excepting, as a hypothesis, these figures are correct, the first question is, did we not expect this, considering the fact it has been ‘warming’ over the last 200 years; and, second, and more importantly, are there ‘anomalies’ in these temperatures and, if so, assuming as such, what do they mean? To me, they mean very little. What is interesting is perhaps there is a turn ‘in the weather’ that the present stability in temperatures may signify. Not because I’m looking for it, in order to ‘disprove’ someone’s theory but because it is objectively interesting. And yet, it seems, climate scientist are really not trying to look. Look!

  19. Based on their graph in Figure SI6, it looks like they’ve used outdated TSI data to force their models. And that’s confirmed based on the discussion on page 3 of the supplemental information, where they write, “The solar forcing is perhaps the most uncertain forcing. Though there is considerable discussion1 about the amplitude of changes in past Total Solar Irradiance (TSI), current estimates seem to support changes in the order of 0.1% of TSI between the late Maunder Minimum and the late 20th century. The CSM simulation used herein incorporates a 0.1 % increase in TSI for this period while the HadCM3 and ECHO-G simulations use 0.25% and 0.3%, respectively.”

  20. Looked at figure S17. Note to self: Consult textbook on the Nyquist Sampling Theorem.
    Second note to self; have a nice glass of red wine instead.
    Come to think of it; the scungiest of all of our mouse camera chips, have a lot more pixels than those cartoons.

  21. The amount of TSI variation may be uncertain and the effect of GCR on cloud cover is still being worked out. However looking at historical radionuclide proxies and ice core temperature reconstructions it is becoming evident that the solar influences the NAM/NAO phase and possibly ENSO. I suspect it is a top down effect from UV, ozone changes but the mechanism is above my understanding. I do not believe it is a coincidence that thirty years of Positive NAO was associated with the modern solar maximum and temperature increase. The sun is now waning and it looks like negative NAO and IPO (La Nina domination) will continue for the next twenty to thirty years and bring global temperatures down.

  22. So, it looks like “models” based on, ( some ), proxies show what they planned to show?
    Did I miss something?

  23. Going on just the info provided in the article above, the methods employed are dramatically insufficient (‘stupidly’ linear) for the job undertaken; however, in fairness to the authors, paywalls (such as those unethically used by Piers Corbyn) should be BANNED to ensure (a) avoidance of resource squandering on wheel reinvention and (b) civilization’s efficient evolution.

  24. Paul Vaughan,
    What point you are making? Might I suggest you withdraw your remark that we ‘unethically charge’ for our forecasts – which appears to be what you mean. Or do you mean weather forecasting is unethical? People who do it have to live don’t they? I trust you will stop shopping, paying VAT and your BBC licence fee because that is going to ‘unethical’ Met Office weather forecasts!
    On the article itself one has to understand that the warmist implied view of the world that what they can’t see (or refuse to see) doesn’t exist, is silly.
    The article states
    “Thus, the detection of a solar response in European summer temperatures remains uncertain”. What is meant by ‘solar’ (ie is the measure appropriate?) and ‘response’ of course depends on many things which can be chosen; but are we to conclude therefore ‘It must be CO2’!
    Readers may be aware that last summer the West Russian heatwave (which we had predicted) was KO-ed when we predicted (Aug 15th) by a double sunspot solar flare which 12 hours later triggered thunderstorms in St Petersburg (or Leningrad for the over 70’s) and subsequent developments which caused the whole Northern hemisphere jet stream to un-jam and change Russia from being hot to cool and the Pakistani super-floods came to an end as well. See http://www.weatheraction.com/docs/WANews10No31.pdf
    THAT was (predictable) hemispheric weather change caused by solar events. Added up such things are climate change driven by solar activity. So, we know it exists.
    Therefore on this paper, either
    (a) the measure of solar activity chosen is one which cannot detect what counts; or
    (b) the methods of detection employed are poor, or
    (c) the solar effect was ‘off’ then and is ‘on’ now, or
    Of course that last one is pretty barmy and I am sure Global warmers would never adopt it.
    Thanks Piers Corbyn, WeatherAction long range forecasters (free to the chosen few)

  25. Piers Corbyn
    It is certainly obscure what meaning was intended by Paul Vaughan in tcalling for the banning of pay-walls that prevent the free exchange of information such as in the research that is the subject of this thread. And probably an even greater waste of bandwidth to speculate why he included you.
    However there is one element of your reputation in this that might have a bearing. Many here reject AGW theory, although often for different reasons. But one common comment that is made compares the efforts to predict weather and climate by the Met Office or other ‘establishment’ sources and your success as ‘one man with a lap-top.’
    I think some may see that as a refutation of the dominant climate theory, that better predictions can be made by your method than a super-computer and a team of specialists. Perhaps there is a sense that if only your method was widely available, requiring apparently no more than modest computing power and a method of applying it, then its superiority over the conventional, and flawed(?), AGW meteorology would be obvious.
    The success of your methods which could presumably be applied by anyone with the requisite data and methodology would discredit AGW theories and perhaps some here resent the fact that commercial realities seem to prevent such a simple means of eliminating the AGW theory being widely promulgated.

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