Did Climate Change Load the Dice for Sandy?

Well, this is Rabett Run, so why ask?  Still, as we say, making the rubble bounce has an instructive effect, so let us bunnies add to the throw weight  In the comments about Eli's post on Testing, whose theme was that damage from extreme events is a question of reinforcement of several things rather than one single driver, Aslak Grinsted pointed to his recent PNAS paper (open access) which analyzed tidal gauge data

Detection and attribution of past changes in cyclone activity are hampered by biased cyclone records due to changes in observational capabilities. Here we construct an independent record of Atlantic tropical cyclone activity on the basis of storm surge statistics from tide gauges. We demonstrate that the major events in our surge index record can be attributed to landfalling tropical cyclones; these events also correspond with the most economically damaging Atlantic cyclones. We find that warm years in general were more active in all cyclone size ranges than cold years. The largest cyclones are most affected by warmer conditions and we detect a statistically significant trend in the frequency of large surge events (roughly corresponding to tropical storm size) since 1923. In particular, we estimate that Katrina-magnitude events have been twice as frequent in warm years compared with cold years (P < 0.02).

Tamino is busy analyzing the data, Eli knows his limits, but consider, Grinsted et al, has shown a correlation between warmer oceans and higher surge and activity.  Since higher sea surface temperatures are a consequence of global warming, well yes, there does appear to be a causal relationship.  There, easy enough.

Still there was something else in that paper which caught the Bunny's eye (he has been looking for a few days) but first some alphabet soup.  The surge index is Grinsted, Moore, and Jevrejevathe's measure of storm surge.  NTC is net tropical cyclone activity, ACE is accumulated cyclone energy and PDI is power dissipation index.  NHD, is net hurricane damage, Ethon's favorite snack food, some thing that Roger keeps pushing as a measure that shows there has been no increase in hurricane activity, and Andy Revkin (you there Andy?) keeps swallowing.  GMJ conclude that

The surge index is positively correlated with all of the comparison measures. The best correlations are found with measures that emphasize intensity (e.g., NTC, ACE, and PDI) and measures that are restricted to US land-falling storms only. Table 1 also shows that low-frequency correlation tends to be at a higher level than the year-to-year correlation. This is to be expected given that there are low-frequency driving agents related to various climate forcings (4, 8). One notable exception is NHD, which shows poor low-frequency correlations. However, NHD has been subjected to extensive corrections for inflation and changes in societal conditions over time (21). These corrections affect primarily low-frequency signals and trends and we interpret the poor low-frequency correlation with surge index to be due to a substantial remaining bias in NHD. We therefore consider the low-frequency variability (i.e., trend) of NHD suspect. We note, however, that the surge index does capture the high-frequency variability in NHD, thus supporting the interpretation that it is truly a proxy for cyclone threat. It is conceivable that the surge index could be used to correct for the remaining bias in NHD.   

Eli and a few others have been pointing out that NHD does not account for systematic improvements in forecasting and early warning, building and structure construction and many other such things.  As elegantly put by the EPA

For example, it is not easy to quantify the extent to which increases in coastal building damage is due to increasing wealth and population growth in vulnerable locations versus an increase in storm intensity. Some authors (e.g., Pielke et al., 2008) divide damage costs by a wealth factor in order to ‘normalize’ the damage costs. However, other factors such as changes in building codes, emergency response, warning systems, etc. also need to be taken into account.

Eli has been known to be a bit blunter, speaking for himself and Nils Simon

First, it is obvious even to a stuffed animal that the costs of flood control and surge barriers to limit damage from storms has increased substantially over the last fifty years. If such expenditures have NOT been included in the storm cost estimates, and the trend without them is flat, the trend WITH such costs MUST increase substantially. Any estimate that neglects these costs must be stated as a LOWER LIMIT. Neither Eli or Nils can find any such statement, not just from Roger Pielke. Therefore in true "Honest Broker" form, Rabett Run concludes that (OK, draw your own conclusions from what Roger calls others who mis-state something)

Second, and this is Nils' insight, NOT to include such costs or deal with their effect when you are aware of them, is either dishonest or a statement that such adaptation has no effect. Since we have been adapting to increased storm damage like crazy. Pielke is in Zugzwang.

but here, for the first time, GMJ have produced a metric which can be used to qualitativefy, or with some more work to quantitatify the benefits of progress.   What they have found makes great sense, if one realizes that the type of improvements the EPA, Nils and Eli were talking about take a long time to appear over the entire country, including the coasts.

That means that the LONG TERM correlations of NHD with physical measures of hurricane damage will be lousy, but short term correlations will be high (or as high as anything else).  NHD in that sense is a measure of the value and density of structures at the time that a hurricane hits, but it is lousy at capturing long term improvements.