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Reading and Writing Exercises on Hurricanes and Global Climate Change, by Mary Savina, Professor of Geology

1. Have Atlantic hurricanes increased in frequency and/or magnitude?

It turns out that the answer to this question probably depends on the period of time you are looking at.

A. The intermediate time scale.

The intermediate time scale (accessible through historical records) is covered in two monographs/websites from the National Oceanic and Atmospheric Administration (NOAA):

  • Jerry D. Jarrell. Jerry D., Mayfield, Max, Rappaport, Edward N., and Landsea, Christopher W., 2005 (update), The Deadliest, Costliest, and Most Intense United States Hurricanes from 1851 to 2004 (and other frequently requested hurricane facts): NOAA Technical Memorandum NWS TPC-4
  • Rappaport, Edward N. and Fernandez-Partagas, 1995, (updated 22 April 1997 by Jack Beven), The Deadliest Atlantic Tropical Cyclones, 1492-1996: NOAA Technical Memorandum NWS NHC 47
    (Note that each section of this paper loads sequentially; there are five sections, plus appendices, acknowledgements and references).

Here are some questions with which to approach these two papers:

  • What geographic areas are covered in these two papers?
  • How do the authors measure deadliness, costliness and intensity (all three are variations of magnitude)? What are some problems with their measurements? What are some alternative measures that might be used?
  • What are the correlations among deadliness, costliness and intensity?
  • Are hurricanes becoming stronger? More frequent?
  • What do these data (and the texts) suggest about changing frequency of hurricanes and major hurricanes?
  • What are the most active and least active months in the hurricane season? Are different parts of the U.S. Coast more susceptible to hurricane strikes at different times of the year?
  • What do the authors of these two papers want readers on the Gulf and Atlantic coasts of the U.S. to know and do?

Before reading the next two papers, you should write a short paragraph about how hurricane numbers and magnitudes have changed since records began to be kept.

B. The short time scale (covered by the instrumental record).

Two influential papers were published in 2005:

  • Emmanuel, Kerry, 2005, Increasing destructiveness of tropical cyclones over the past 30 years: Nature, v. 436, p. 686-688 (issue of August 4 2005) doi:10.1038/nature03906 (from the Bridge, do a title search on Nature in Serials/Periodicals, hit the first link, and then scroll down to item 6 – Nature Online. Click on “Carleton subscribes through Nature Publishing” and go to archives to find the August 4 2005 issue. If you have any problems, see a reference librarian).
  • P. J. Webster, G. J. Holland, J. A. Curry, H.-R. Chang, 2005, Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment: Science, v. 309, no. 5742, p. 1844-1846. (Carleton also has an online subscription to Science).

Here are some questions with which to approach these two papers:

  • What are the different data sources and analysis techniques used by the authors of the two papers?
  • What is the time period of the data that are analyzed in the papers?
  • What are Emmanuel’s and Webster, et al.’s measures of hurricane magnitude and how do they compare to those used in the NOAA papers?
  • How does Emmanuel generate the data shown in the three graphs? To what does he attribute the increase in power dissipation (as he defines it)? How does Sea Surface Temperature (SST) correlate with power dissipation?
  • Do data from earlier periods (1492 and on) suggest that 1970-2003 is a period characterized by unusually numerous and intense hurricanes? How do these data inform your “read” of Emmanuel’s and Webster et al.’s conclusions?
  • What do Emmanuel and Webster, et al. say about the relationship between hurricanes and global warming?

C. The LOOOOONG Time Scale.

Geologists are fond of using the present to interpret the past (reasoning, for instance, that streams 50 million years ago were probably a lot like streams on today’s earth). It’s also possible to look at the records of the past to gain insight about the present. Here’s a short summary article from Science News about hurricanes in the Gulf of Mexico over the last 5000 years or so:

Two of the papers on which the Science News article is based are:

  • Liu, Kam-biu and Miriam L. Fearn, 2000, Reconstruction of prehistoric landfall frequencies of catastrophic hurricanes in northwestern Florida from lake sediment records: Quaternary Research v. 54, p. 238-245.Note that there’s a Discussion and Reply for this article, also in Quaternary Research, May 2002, v. 57, p. 425-431.
  • Liu, Kam-biu and Miriam L. Fearn, 1993, Lake-sediment Record of late Holocene Hurricane Activities from Coastal Alabama: Geology, v. 21, p. 793-796.

Questions for these papers:

  • What is the sedimentary record of known, recent hurricanes?
  • What are the features used by these scientists to infer past hurricanes? How do they measure magnitude?
  • What do these authors conclude about hurricane frequencies and magnitude through the last 5000 years?

If the Science News article sparks your interest, here are a couple of basic sources from the Paleotempestology (literally: old storms) pages of the NOAA website and a pretty good bibliography of other papers up through 2000, compiled for the insurance industry

2. Is global climate change responsible for increasing hurricane magnitude and/or frequency?

Some of the 2005 papers go beyond the analysis of magnitude and frequency to hypothesize about the causes of changed hurricane strength. (For instance, what is Kerry Emanuel’s position?) Certainly, this connection was made in numerous post-Katrina articles in the popular and science press. Here’s an alternative viewpoint:

This paper has useful definitions of “event risk,” “vulnerability” and “outcome risk”. Note, too, the authors’ definitions of hurricane intensity and frequency. The authors also distinguish among evidence from theory, modeling and empirical measurements. Into which of these categories does the information the earlier cited papers fall?

  • What are the authors’ conclusions about trends in hurricane frequency and intensity? How do these match the conclusions you have drawn from reading the other papers?
  • What do theoretical and modeling studies cited by the authors suggest about the likely increase in wind speed as a result of global warming? Is this a big effect or a small effect relative to other effects on “outcome risk”?
  • Why do the authors think it’s a bad idea to use hurricane patterns to justify particular energy policies? Do you agree?

Roger Pielke, Jr., lead author on the BAMS paper, also has a climate discussion blog on which you’ll find some interesting material about the genesis of this paper as well as the differing opinions about global climate change, hurricanes and strategies for rebuilding:

3. Okay, now that you’re an expert on hurricane magnitude and frequency, what do you think policy makers should do about development and re-development on the Gulf and Atlantic Coasts?