Since I’ve been asked a few times I thought that it might be worth posting an analysis of hurricanes and climate change from work I’ve been involved in. Below is an extended excerpt from a 1999 paper I collaborated on, looking at trends in hurricane incidence and their policy relevance. Even though the paper was published more than five years ago, I think that the analysis remains sound.

Landsea, C. L., R. A. Pielke, Jr., A. Mestas-Nuñez, and J. Knaff, 1999: Atlantic Basin Hurricanes: Indicies of Climate Changes. Climate Change, 42, 89-129.

Here is a link to the paper in PDF.

The paper can also be found here in HTML.

Begin extended except …

“Climate change policy

In 1996, Working Group III of the IPCC estimated increased worldwide damages and loss of life related to hurricane impacts in a doubled CO2 world at $630 million and 8,000 additional lives lost (Watson et al. 1996). Working Group III concluded that these economic losses and lives lost would be prevented with the adoption of emissions reductions policies. There is an obvious inconsistency between the projections by IPCC Working Group III of increased impacts and the conclusions of Working Group I, which stated that “the state of the science does not allow assessment of future changes” in tropical cyclone indices.

Setting aside for the moment this inconsistency, the logic of the IPCC Working Group III is fundamentally flawed. Even if there were valid theoretical reasons to expect more tropical cyclones in the future related to human-caused climate change, the climatological record gives no indication that society can modulate hurricane impacts through energy policies. That is, as atmospheric CO2 levels have increased, “there is currently no evidence that there has been systematic changes in the observed tropical cyclones around the globe” (Landsea 1998). The suggestion by the IPCC that a reduction in greenhouse gas emissions will lead to less or less intense tropical cyclones and therefore less impacts to society begs several further questions of relevance to the policy community which have thus far gone unasked and unanswered:

Can the scientific community reliably differentiate future hurricane frequencies and magnitudes based on the various scenarios of greenhouse gas emissions and concentrations (i.e., IS92a-f from Houghton et al. 1992)?

The analysis of climatological information presented in this paper suggests that for many decades to come, detection of a human-forced signal in the tropical cyclone record will be extremely difficult to detect because of both the relatively modest size of the predicted changes in MPI and the rather large apparently natural multidecadal variability (cf. Henderson-Sellers et al. 1998). Therefore, it is unrealistic for policy makers to expect in the near term (i.e., in the next few years) that the scientific community will be able to reliably predict future hurricane incidences differentiated by various emissions scenarios. As Henderson-Sellers et al. (1998) have noted “global and mesoscale model-based predictions for tropical cyclones in greenhouse conditions have not yet demonstrated prediction skill.”

Is there reason to believe that policy makers should expect the policy actions now being contemplated (e.g., the Kyoto Accord to the Framework Convention on Climate Change) will reduce the number of and intensities of future hurricanes that will impact society?

There is no evidence to suggest that society can intentionally modulate tropical cyclone frequencies and magnitudes through energy policies2. Therefore, policy responses to hurricanes ought to focus on the reduction of society’s vulnerability to hurricanes, rather than on prevention of the storms themselves (Pielke and Pielke 1997b). For instance, in the context of insurance, Henderson-Sellers et al. (1998) recommend a focus on “appropriate reserves and restrictive underwriting” rather than on accurate predictions, or by extension, on controlling future hurricane incidences.

Answers to these questions do not exclude the possibility that an anthropogenic forcing might lead to changes (Henderson-Sellers et al. 1998). They do strongly suggest that reliable prediction of future hurricane indices (much less societal impacts) differentiated by various emissions scenarios is beyond the capabilities of the scientific community. Further, if a policy objective is to reduce society’s vulnerability to hurricane impacts, then decision makers would be wiser to consider better adapting to documented variability, rather than preventing storms from occurring (Pielke 1998)3.

Natural disaster policy

One of the most striking features of the information presented in section four of this paper are the 19 years which passed between intense hurricane landfalls on the U.S. East Coast from 1966 through 1984. These decades saw much of the population growth and development of coastal communities. Overall, the 19 years prior to 1966 saw 14 intense hurricanes strike the U.S. East Coast. Most of the historical economic losses are the result of storms striking the U.S. East Coast rather than the Gulf Coast (Table 7). Consider also that over the seven year period 1944 to 1950, the state of Florida saw $44.2 billion (normalized to 1995 values, see Pielke and Landsea 1998) in losses, or more than $6 billion per year, while the 46 year period 1951 to 1997 saw a similar total amount of normalized damages, $49.3 billion or about $1.1 billion per year. Most of the damages of the latter period were the result of Hurricane Andrew in 1992.

The review of indices for hurricane climatic changes reveals that from the perspective of societal impacts, recent decades are indeed anomalous. But contrary to conventional wisdom of some in the media, public, and policy communities, recent decades are unique because of the relative infrequency of U.S. landfalls of strong hurricanes, and not because of any upsurge in strong storms (cf. Landsea et al. 1996). Hurricanes arguably are the natural hazard with the greatest potential for economic disruption in the United States, and further, the potential for a large loss of life related to a hurricane’s landfall is increasing with coastal development (Pielke and Pielke 1997a). Because the nation’s hurricane policies have been typically developed in the immediate aftermath of a disaster (Birkland 1997, Simpson 1998), it would be prudent for the policy community to assess whether or not the lack of hurricane impacts in recent decades has led to an atrophying of the nation’s hurricane policies. Some questions to consider include:

Are national, state, and local hurricane policies supported by public and private decision makers in a manner commensurate with the documented vulnerability of society?

How prepared is the U.S. east coast for 14 intense hurricanes in 19 years as occurred in the 1940s-1960s?

How prepared is the nation, and Florida specifically, for a recurrence of the hurricanes of the late 1940s?

Is the time ripe for the United States to develop a national hurricane policy?

Asking and answering questions like these are important steps in reducing the nation’s vulnerabilities to hurricane impacts. One benefit of past hurricane impacts is that society has learned many lessons. These lessons provide a basis of experience on which to reduce the nation’s vulnerability to hurricane impacts (Pielke and Pielke 1997a). What seems to be lacking is awareness of whether the nation’s risk is matched by its response.”

… end of extended excerpt.