10 April 2013

Fool Me Once: Munich Re's Thunderstorm Claims

Last October Munich Re, one of the world's largest reinsurance companies, issued a press release in which they made a remarkable claim about a new study of normalized economic losses related to thunderstorms in the United States:
In all likelihood, we have to regard this finding as an initial climate-change footprint in our US loss data from the last four decades.
To date no studies of economic losses associated with weather events have successfully identified a signal of human-caused climate change in loss data. This conclusion was underscored by the IPCC which surveyed the literature and concluded in its 2012 Special Report on Extreme Events that "Long-term trends in economic disaster losses adjusted for wealth and population increases have not been attributed to climate change, but a role for climate change has not been excluded."

The claimed discovery was thus of tremendous significance. But fantastic claims before peer review deserve, as Andy Revkin has warned, caution.
Munich Re did prepare a report (which was not made readily available) in conjunction with its press release, but no peer reviewed paper. They later promised that peer reviewed support for the claim would soon be forthcoming:
[Ernst] Rauch [head of Munich Re's Climate Center] said Munich Re researchers have submitted a paper for peer review that shows how climate change is resulting in intensifying storms in the United States. The forthcoming study, he says, points for one of the first times "toward an attribution of climate change to losses."
This week, the promised study -- Sander et al. 2013, hereafter SEFS13 -- was published in the journal Weather, Climate and Society of the American Meteorological Society. Munich Re subsequently issued the press release that you see at the top of this post titled, "Climate change effects increasingly influencing US thunderstorms."

If you like stories with happy endings, then this would be the time where you should stop reading this post, to take a nod from Peter Falk in The Princess Bride.
As one looks a little bit closer at the public representations made by Munich Re about the paper and the paper itself, one quickly finds -- as is all too common in climate science -- that the strong public claims simply cannot be supported by the actual research, and the paper suffers from an obvious fatal error. Let's have a look.

The further one reads into the press release the further it deviates from the claim expressed in its title. The paper says the following about attribution of loss trends:
[A] high probability is assigned to climatic variations primarily driving the changes in normalized losses since 1970. Due to the chosen methodology, the current study has not been able to conclusively attribute the variability in severe thunderstorm forcing situations and losses to either natural climate variability or anthropogenic climate change.
Got that? The paper says nothing conclusive about attribution. It is not an "initial climate change footprint." It does not support the claim that "climate change effects increasingly influencing US thunderstorm losses."

In fact, the paper says much the opposite: attribution of losses to climate change was not achieved in the paper. Perhaps the media is getting wise to these games, because there has been almost no media coverage of the sensational claim trumpeted in the headline of the press release put out a few days ago -- a claim, which if it were correct, would deserve broad coverage.

But it gets worse.

The paper argues that the causal mechanism leading to greater thunderstorm variability is the frequent claim that it is the consequence of an atmosphere holding more water vapor:
Trapp et al. (2007, 2009) have found that climate-model-based projections display indications of a regime in which increasing specific humidity (as the main contributor to increasing CAPEml over time) increases the annual frequency of severe thunderstorm environments (defined by the product of CAPEml and DLS) in a transient climate model experiment since 1950.
The paper further explains:
As a precondition of rising CAPEml, monthly observations of near surface specific humidity during the period 1973–1999 (HadCRUH, Peterson et al. 2011) show a clear increase in the Northern Hemisphere. In eastern North America this increase equals 3.6 (±2.7) %. This was shown to be in coarse statistical agreement with the results from (anthropogenically forced) GCM runs over this period (Willett et al. 2010).
It is here where the reader of the paper might find themself being taken for a fool.

Willett et al. 2010, the source cited by SEFS13, provides estimates for changes in "near surface specific humidity" for a large number of regions around the world, as shown in the figure below.
Eastern North America, which is cited explicitly in SEFS13, is found where you would expect it and is labelled ENA. You might wonder why SEFS13 did not say anything about CNA- Central North America, which is otherwise known as "tornado alley." I sure did.

Immediately below is a zoomed-in image of North America taken from the image above. Immediately below that I show Figure 1 from SEFS13 -- which shows the location of the normalized loss events included in its study -- with my overlay of the Willetts et al. 2010 CNA region (which stretches from the Florida panhandle to the Texas panhandle, and then goes north to the Canadian border through eastern Colorado) highlighted as the transparent blue box.

You can clearly see that the vast majority of normalized US thunderstorm losses actually occurs in Central North America -- CNA. This conclusion is insensitive to small errors in the mapping of the CNA region onto SEFS13 Figure 1.

So, what do Willetts et al. 2010 actually say about changes in "near surface specific humidity" in the CNA region 1973-1999?

It is not hard to find as it appears in the same table as the ENA data which was reported by SEFS13. In fact, it appears in the row just above. It says that there has been no change in "near surface specific humidity" in Central North America 1973 to 1999. The numbers are 1.9 (±4.1) %. Surprised?

So let's recap:
  • Munich Re claimed to have discovered the first "climate change footprint" in economic loss data.
    • That was incorrect.
  • Munich Re claimed in the headline of the press released announcing SEFS13 that "climate change effects increasingly influencing US thunderstorms."
    • That turns out not to be supported by the paper, which actually concludes the opposite.
  • SEFS13 argues a causal mechanism between increasing humidity, thunderstorm variability and by extension, to normalized losses.
    • The paper fails to report that in the region where most US thunderstorm activity and damage has occurred, the data shows no change in humidity 1973 to 1999 -- undercutting its core argument. The paper reports data for an accompanying region where there has been an increase in humidity, but very few losses.
Misleading public claims. An over-hyped press release. A paper which neglects to include materially relevant and contradictory information central to its core argument. All in all, just a normal day in climate science!


  1. Great work Roger. It's not like an insurance company to less than 100% straight. Very disappointed.

  2. is there a data file anywhere of actual thunderstorm counts over time? I suspect there is not, but if one exists I'd like to see what it says when plotted. - Anthony

  3. Funny thing - there's Big Oil, Big Tobacco and Big Pharma, but I've never seen a reference to Big Insurance.

  4. How would ANY study, in principle, unambiguously attribute economic losses associated with weather events to human-caused climate change?

  5. Quoting: they say "Due to the chosen methodology, the current study has not been able to conclusively attribute the variability in severe thunderstorm forcing situations and losses to either natural climate variability or anthropogenic climate change.".

    Because they say the failure of attribution is "due to their chosen methodology", they presumably think here is another methodology that CAN conclusively attribute.

    FWIW, I don't see it either.

  6. "Nevertheless, the expected impacts of anthropogenic climate change on the forcing of convective storms appear consistent with these findings."

    Sander et al. 2013

  7. Muller has a great lecture on energy and climate issues from about 4 years ago where he deconstructs similar claims in Alpha Gore's work of fiction for which he won the Nobel Prize. Tornadoes was the first thing he looked at and looked at National Weather Service data on numbers of damaging tornadoes and found a small decreasing trend. Next he looked at hurricanes making US landfall for which we have very good records. Categories 1-5 had a decreasing trend as did Cat 4-5's. Gore got it wrong again. It appears that Gore was using total number of hurricanes. Muller points out that before satelites, there were no tracks in the middle of the Atlantic whereas recently there were huge numbers. He observed that the only way hurricanes in the ocean were detected before satellites was from ship reports, and the ships avoided these areas because of hurricanes!!! He also did wildfires. Once again, Gore cherry picked his data.

    And the Climate science Team said nothing about all this. Is it any wonder climate science has a reputation only a little bit higher than used car salesmen. This is not a problem with "communication" but a problem with plain old fashioned misrepresentation in the service of a "noble cause." I don't see how these people expect to be taken seriously until they clean up their own house.

  8. Recalling past IPCC language, can't they well say from this paper:

    "The global warming footprint as seen through increasing thunderstorm losses can now conclusively not be ruled out, and more light is being shined in this area...Many parts of the world are already seeing increases in thunderstorm forcings..."

    ... that sort of thing...

  9. - Roger

    I suppose the studies of political science and politicking are very different. Clearly your credentials are in the former.

    Just a normal day in climate science, somebody is angry at Pielke, Jr. But thanks for keeping them honest.

  10. The same behavior occurs in the world of advertising, where it has been seen that:
    "The Large print giveth,
    The Small print taketh away."

  11. "What, no attribution to AGW? Inconceivable!"

  12. "No final attribution of the climatic variability identified in thunderstorm forcing and losses – neither to natural climate variability nor to anthropogenic climate change – can be conclusively arrived at in this study due to the chosen methodology. Nevertheless, the expected impacts of anthropogenic climate change on the forcing of convective storms appear consistent with these findings."

    It seems your reading is that for a paper to show a relationship it must be "conclusive". However, if the authors intend "conclusive" to mean 100% as opposed to 99.99% or 95% likely then I think this may be the reason for the disconnect here.

  13. Roger,

    The interesting finding, that you did not highlight (wink), is that they find an increase in damages since 1970 even after applyling your normalization methodology from your 2008 paper. They say:

    "From these findings we conclude that it is predominantly the change in hazard over time – rather than the change in destructible wealth or vulnerability – that has driven up normalized losses, as reflected in the strong similarity of the longer-term signals in Fig. 8."

    Now how did that key finding go unnoticed by you in your blog post? ;)

    To reiterate, they do find that the environment/climate in which the damaging storms are developing has changed. They say:
    "As a conclusion, a high probability is assigned to climatic variations primarily driving the changes in normalized losses since 1970."

    What they didn't try and determine is whether or not that change in the severe thunderstorm climate regime is anthropogenic or natural, and nowhere in the paper or the press release do they refer to anthropogenic climate change causing the changes storm environment. However, and this is critical, the observed changes (e.g., increasing CAPE) are consistent with the theory and expected changes as a result of AGW. They say that in the paper and in the final sentence of the abstract:

    "Nevertheless, the expected impacts of anthropogenic climate change on the forcing of convective storms appear consistent with these findings."

    CAPE, which they use in their study, is modulated by a great degree by low-level moisture (in their case the lowest 100 mb above the surface). So the NCEP-NCAR reanalysis must be showing an increase in low-level moisture to facilitate an increase in CAPE. One can increase CAPE by warming the low-levels and cooling temperature aloft (differential heating), but the impact of changing low-level moisture has by far a greater impact on CAPE than does the differential heating. Indeed if one looks at the 850-mb specific humidity in the NCAR-NCAR reanalysis data between 1970 and 2009, there is a clear increase in the specific humidity over the "CNA" region for the March-September period.

    What I do take issue with in their paper is their use of Willett et al. (2010). That paper looked only at annual trends up until 1999, whereas this paper looks at data through 2009 and for March through September (i.e., not annual). Other papers have extended the analysis out further in time or have used different data. Brown and DeGaetano (2013) find statistically significant increases in the surface dewpoint over the "CNA" region (see their Fig. 7) in the spring (MAM) and summer (JJA) between 1947 and 2010. Further, Durre et al. (2009) found an increase in column-integrated water vapor below 500 mb (Fig. 3c in Durre et al. 2009, JGR) at some sites within the "CNA" region for the summer months between 1973 and 2006.

    So the authors should have either cited a more appropriate paper and/or or shown the trends in the low-level moisture over their study area and time window from the NCEP-NCAR reanalysis data that they used. But this is hardly controversial and in no way undermines their findings.

    This is just another example of certain opportunists pouncing on an inconvenient paper to advance their agenda against climate scientists, through a willful misinterpretation and twisting of the paper and associated press release.

    Roger what this amounts to is you making a straw man argument here about "attribution", and then going on to make sweeping derogatory generalizations about climate science. Shameful and desperate antics by you in my opinion.


    PS: In your conclusions you should be referring to "specific humidity" and not "humidity, they are very different things.

  14. Munich Re is a publicly listed company ... this amounts to issuing misleading information about its financial performance ie., blaming climate change (beyond its control) rather than its own incompetence for losses. Time that the regulators took an interest in this fraud.

  15. Egos, competition for bucks, and the public relations mill make for difficulties with straightforward but unexplosive interpretations everywhere, not just climate science.

    It would be great if a beneficent foundation would fund a site where press releases of new scientific findings could be posted and others might weigh in on a more systematic basis, rather than occassionally on different blogs.

    Then people would know every time they saw a press release that seems particularly out of line with what was previously known, that they could easily find the rest of the story.

  16. Roger, maybe you're not doing the new MR press release proper credit. It said: "The study was not able to conclusively differentiate in the climatological forcing of loss changes between the natural and the man-made components of climate change."

    The subtle difference is between climate change (including natural variability), and anthropogenic climate change, for which neither the press release nor the paper provide sufficient support. Despite the hints made about "consistent with what we would expect" etc. Also the paper is quite careful in its wording.

    So it seems: some more evidence of signals of climate variability in loss records, but not yet from anthropogenic changes. This work is laudable though, as thunderstorm impacts are more closely related to temperature change than many other hazards (storm, flood).

    This is also what we would expect, as shown from other studies; see my paper here: http://dx.doi.org/10.1111/j.1539-6924.2012.01880.x

    BTW: the right link for the October press release which hinted at an "initial" footprint is her: http://www.munichre.com/en/media_relations/press_releases/2012/2012_10_17_press_release.aspx

  17. -16-Laurens

    Thanks for your comment. As I wrote in the post, the deeper one reads into the press release and the paper the more the text differs from the headline -- not good practice. The paper also has a fatal methodological flaw as I have indicated.

    I'll fix that lost link!


  18. Lindzen tells us that textbook theory says that storms should be less frequent with increasing temperature yet some other chaps seem to frequently claim the opposite, yet not apparently from textbooks. Is it perhaps just too easy to claim "the science says" or "theory says" without actually bothering to tell us which science or which theory? Don't they really mean "pessimism dictates"!

  19. Is there a possibility to sue Munich Re for possibly inflated insurance rates or other public or personal spending which was based on their untrue research ?