23 August 2010

Disaster Losses and Climate Change

[UPDATE: The NYT's Andy Revkin covers the new article here.]

The Bulletin of the American Meteorological Society has just put online a review paper (peer reviewed) by Laurens Bouwer, of the Institute for Environmental Studies at  Vrije Universiteit in Amsterdam, titled, "Have disaster losses increased due to anthropogenic climate change?".  

Readers of this blog already know the answer to this question, and here is Bouwers' conclusion:
The analysis of twenty-two disaster loss studies shows that economic losses from various weather related natural hazards, such as storms, tropical cyclones, floods, and small-scale weather events such as wildfires and hailstorms, have increased around the globe. The studies show no trends in losses, corrected for changes (increases) in population and capital at risk, that could be attributed to anthropogenic climate change. Therefore it can be concluded that anthropogenic climate change so far has not had a significant impact on losses from natural disasters.
Bouwers rightly acknowledges that there are uncertainties in such studies, and in particular, there will be a need to refine efforts to evaluate changing vulnerability and exposure in future such work, especially as the signal of greenhouse gas driven climate change is expected to become larger.  However, such uncertainties are not presently so large as to undercut Bouwers' conclusion, e.g.,
A rigorous check on the potential introduction of bias from a failure to consider vulnerability reduction in normalization methods is to compare trends in geophysical variables with those in the normalized data. Normalized hurricane losses for instance match with variability in hurricane landfalls (Pielke et al. 2008). If vulnerability reduction would have resulted in a bias, it would show itself as a divergence between the geophysical and normalized loss data. In this case, the effects of vulnerability reduction apparently are not so large as to introduce a bias.
A pre-publication version of the paper is available here in PDF.

Bouwer, L.M. (in press). Have disaster losses increased due to anthropogenic climate change? Bulletin of the American Meteorological Society, doi:10.1175/2010BAMS3092.1.


  1. Very nice vindication of your earlier work.

  2. What's amusing is to see the Munich Re label on the graph. Just like Swiss Re, Munich Re has been playing the linkage of storms to climate change theme.

  3. You tend to be very careful with your wording to say that no AGW signal can be identified in the overall data. This doesn't necessarily mean that there is no impact, just that that the overall data set is too noisy to find it if it exists.

    Extreme events are by their nature not numerous, so the sample is small and their signal is very noisy. As with issues in some areas of epidemiology, not finding a signal doesn't mean one isn't there. the conditions of the search are not conducive.

    Just imagine a telephone poll where you could only call 50 people. The percent uncertainty would be quite large, and it would be hard to say with any certainty what the majority opinion was. But that doesn't mean they don't have an opinion.

  4. Well said Dean. While Roger is quite right in pointing out that no signal has yet been found, that is not the same thing as saying that we don't expect one to be found in the future.

  5. Dean and Marlowe,

    I use the same sort of logic when I buy lottery tickets. My wife just doesn't get it.

  6. -5- John,

    I, too, use similar arguments with my wife about my efforts to clean up the messes that inexplicably accumulate in my wake. Alas, she is not as sophisticated as climate scientists, and is unkind enough to note that whatever the effects of my cleaning may be, they are undetectable, and therefore insignificant.

    But Dean's argument is brilliant just because it loses no real punch when substituting just about anything:

    * carbon dioxide
    * ozone holes
    * length of mini-skirts
    * butterflies in China

  7. Matt - That's the nature of proving a negative. Not finding proof that something is causing something else doesn't prove that it isn't. But unlike the length of mini-skirts, there is a plausible cause-and-effect hypothesis for AGW and extreme events, particularly heat waves, floods, and droughts.

  8. Dean said... 7

    "But unlike the length of mini-skirts, there is a plausible cause-and-effect hypothesis for AGW and extreme events, particularly heat waves, floods, and droughts."

    I usually find it a painful experience when I come home from visiting my parents, I smell like perfume(my mothers) and I have lipstick on my cheek(again my mothers).

    Of course a plausible cause and effect would be that I was having an affair and that the trip to visit my parents was just a ruse.

  9. -7- Dean,

    Plausible causality or not, insignificant is still insignificant.

  10. Just like I keep telling my wife, she can't ***prove*** I'm not going to win the lottery. And I keep tellin' her, there are plausible statistics that say there's a non-zero chance that I'm gonna win...

  11. Have a look at this from the European Environmental Agency:

  12. @Dean,
    You sort of sum up perfectly the problem of the social movement of AGW:
    Believers keep demanding that society turn its energy economy on its head for a problem that is subtle it cannot be seen in the noise, while ignoring problems that are actually impacting people's lives.
    It sort of raises the question about the reinsurance companies' ability to measure other risks.

  13. #11 Pétur:

    The "climate factors" that the European Commission implies can also be natural climatic variations; i.e. the extreme flood that took place in 2002, not necessarily linked to global warming.

    Also, the EEA has put out more nuanced statements; for example: "...it is still
    not possible to determine the proportion of the
    increase in damages that might be attributed to
    anthropogenic climate change."

    See page 169 in http://www.eea.europa.eu/publications/eea_report_2008_4/pp161-192CC2008Ch6_7Adaptation_Consequences.pdf

  14. Folks, the probability of impact is far higher than winning the lottery and the magnitude of that impact is far greater than insignificant. This thread isn't about the basic science, so I'm not going to be drawn into a debate about that here.

    I remember that Roger told me some time ago on his blog that while the signal cannot yet be identified, he hoped to be the person who some day finds it, which says something about the odds of there being a signal to find.

    The state of the science is that it is plausible and reasonable - likely I would say - to expect the AGW-extreme-event signal to eventually show itself above the noise for at least some kinds of extreme events. But we're not there yet, and the nature of the sample that we have makes it a very difficult challenge.

  15. Dean,

    Since someone wins the lottery almost every week, and since we've never seen any signal of AGW in extreme weather events, it's purely conjectural. So I'm not so certain that the probability is higher, since the probability of AGW signal showing through could, in fact, be zero.

    It may yet happen, nevertheless, though there's still the thorny issue of the 'A' in AGW. For instance (to take an extreme example) I'd expect more of these heat waves in an interglacial than an ice age, and that would certainly be a climate-related signal. But that's just plain old GW (or has been anyways).

    The only thing that Roger's statement says is that Roger thinks (or at least thought) that there is a signal.

  16. One other thing I would add. This thread is about extreme event losses - meaning I think casualties and financial losses. If and when a signal is found for the events themselves, finding that signal for losses faces additional confounding factors for things like population, where building occurs, overall GDP levels, and even currency valuation and conversions.

    Finding such a signal with high statistical significance may be harder than, well, using different sets of proxies to reconstruct temperature over the last 2000 years. ;) At least that one doesn't get into economics. But I doubt that insurance companies will wait that long.

  17. Well, as far as comparing to proxy reconstructions, I suspect the economic data will at least be better than the temperature proxies. :)

    I'd expect the extreme losses not to be more extreme from the magnitude of the events, but from increased frequency. Things like floods are probably not the best candidates for this analysis (as I think Dean has been arguing). But, to pick a random example, hurricane season comes each year. Which is perhaps one reason why this sort of research has focused on hurricanes.

    But the hedging regarding confounding factors such as development is really just another way of saying that any AGW signal is relatively insignificant.

    In any case, I doubt that anyone would really argue that given a significantly different climate, we could expect different frequencies of extreme climate related events. It's certainly possible that for some, the signal will be good news.

  18. "Well said Dean. While Roger is quite right in pointing out that no signal has yet been found, that is not the same thing as saying that we don't expect one to be found in the future."

    But he can (and has) said that even if a signal is found in the future (and it is an increase rather than a decrease), it is likely to still be less significant than changes due to societal changes (e.g., the number of people and value of property near the coasts).

    And conversely, there is good reason to believe that the number of lives lost and damage produced could go down--perhaps even significantly--even if the number and intensity of severe weather events went up.

  19. The opportunity cost of insurance companies preparing for things that are not happening is not insignificant. Investments in the hurricane basins sould be adversely impacted, hurting the jobs and livelihoods of millions of people. All for womething that even apologists agree is not a discernible trend, depite predictions that by now there would be dramatic changes. That frankly seems to be an approach lacking in rationality.

  20. No signal has been found because there isn't one to find. Natural variability will always outweigh Man's puny influence.

  21. The same arguments can be made about long term sea level rise from GW versus short term floods. The effects of the former are certainly insignificant compared to the latter but touted as being something to worry far more about. Priorities?

    Of course there's the coming tipping point that's always just 10 years away.

  22. "No signal has been found because there isn't one to find. Natural variability will always outweigh Man's puny influence."

    This is much like what they said about air and water pollution decades ago in fighting the clean air and water acts. It's a phase and it will pass.

    Extreme weather events are not the only case for taking action. Long-term measurable empirical changes due to AGW are well demonstrated, and also make the case. Evidence regarding extreme events gets a lot of coverage and attention because such events are more dramatic. But it is the icing on the cake of the case for taking action.

    "But he can (and has) said that even if a signal is found in the future (and it is an increase rather than a decrease), it is likely to still be less significant than changes due to societal changes (e.g., the number of people and value of property near the coasts)."

    I'm not sure that I agree with this, and the magnitude will vary a lot geographically.

  23. -22- Dean,

    While people may have denied that pollution was significant in the grand scheme, at least, I am sure, they were able to find it.

    "Long-term measurable empirical changes due to AGW are well demonstrated, and also make the case."

    Again, if you left out the A in the AGW, you'd have a stronger case. But the only justification I've seen for "well demonstrated" comes down to some computer models and the claim that, "We can't think of anything else." We don't even know the sign of some climatic drivers.

  24. "Global warming can be happening without any extra carbon dioxide in the air, simply because of natural variability. Yet it is the widespread belief that the two are related (funny enough without a sound scientific proof!). There are of course some physical mechanisms that will relate increased concentrations in carbon dioxide and warmer surface temperatures, but climate is a... very complicated thing"
    Professor Anastasios Tsonis
    Dept. of Mathematical Sciences, Atmospheric Sciences Group
    University of Wisconsin-Milwaukee
    (written in 2002)

    Like it or not, despite all the handwaving, that remains the actual scientific position. Since then of course there hasn't even been any warming of any kind, and the explanation for that has been....natural variation. Tsonis and Swanson have even developed a plausible idea of what may drive much of this natural variation.

    So, despite all the money spent, we have not identified anything about the influence of CO2 that cannot also be put down to nature. Some people pretend they can separate out natural variation with models but they don't avtually believe it; the hype is just meant to fool the plebs who know nothing about the models.

    CO2 is apparently accumulating in the atmosphere because nature inexplicably cannot cope with our measly extra 2%. And thats the hard science over, the rest is largely guesswork disguised by mathematics to make it look less like guesswork.

    Despite all the empty rhetoric by politicians anxious to be all things to all men, this reality is becoming more clear daily to everyone. The only scary climate argument left is that we are perturbing an unpredictable system. Though frankly even the peak oil argument is scarier than that.

    So policywise, be prepared for massive disappointments. At this point those of us keen on green energy have to argue on benefits and costs, not on scary climate scenarios.

  25. I think the AGW crowd will deeply regret comparing pollution and AGW.
    Pollution can be measured. AGW is not, as any reasonable person admits, something that can be measured.
    Pollution can be linked directly to disease, environmental degradation, human suffering, etc. AGW can be linked back to nothing other than computer models. Perhaps if people were more interested in practical flood control, the Pakistani floods could have been mitigated. Instead, rich nations are flying their high level opinion leaders around to endless conferences to talk about sea levels and climate in 100 or more years. Meanwhile flooding, not sea levels, remains a real problem. But thanks to AGW that real problem is ignored, while future possible problems of dubious credibility takes up too many people's attention.