No Long-Term Trend in Frequency, Strength of Landfalling Hurricanes

by Marlo Lewis on December 17, 2012

in Features

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Numerous politicians, pundits, and activists, and even some scientists blame fossil-fuel emissions for the death and devastation wrought by Hurricane Sandy. Such allegations are ideological, not scientific.

As noted previously on this blog, when hurricane damages are adjusted (“normalized”) to account for changes in population, per capita income, and the consumer price index, there is no long-term trend such as might indicate an increase in hurricane frequency or power related to global climate change.

Moreover, 370 years of tropical cyclone data from the Lesser Antilles (the eastern Caribbean island chain that bisects the main development region for landfalling U.S. hurricanes) show no long-term trend in either power or frequency but a 50- to 70-year wave pattern associated with the Atlantic Multidecadal Oscillation, a mode of natural climate variability. 

A new study by Jessica Weinkle (University of Colorado), Ryan Maue (Naval Research Laboratory), and Roger Pielke, Jr. (University of Colorado) dumps more cold water on claims that global warming significantly (detectably) influences hurricane behavior.

The researchers examined data on the number and power of hurricanes making landfall in the five main hurricane basins: North Atlantic, northeastern Pacific, western North Pacific, northern Indian Ocean, and Southern Hemisphere. The data extend back to 1944 for the North Atlantic, to 1950 for the northeastern Pacific, and to 1970 for the other basins. The data for all basins is current through 2010.

Here’s what Weinkle, Maue, and Pielke, Jr. found:  

We have identified considerable interannual variability in the frequency of global hurricane landfalls; but within the resolution of the available data, our evidence does not support the presence of significant long-period global or individual basin linear trends for minor, major, or total hurricanes within the period(s) covered by the available quality data. Therefore, our long-period analysis does not support claims that increasing TC [tropical cyclone] landfall frequency or landfall intensity has contributed to concomitantly increasing economic losses.

Figure explanation: Red bars indicate the number of major (category 3-5) hurricanes, blue bars indicate the number of minor (category 1-2) hurricanes.

Pielke Jr.’s blog provides an update for North Atlantic hurricanes through November 2012. Extending the study period to include Hurricane Sandy (which, incidentally, was downgraded to a tropical storm by the time it made landfall) doth not a long-term trend make!

Pielke, Jr. points out some interesting details from the updated study, such as:

  • 1971 had the most global landfalls with 30, far exceeding the second place, 25 in 1996.
  • 2011 tied for second place for the fewest global landfalls with 10 (and 3 were intense, tying 1973, 1981 and 2002). 
  • The US is currently in the midst of the longest streak ever recorded without an intense hurricane landfall. 
  • There have been frequent four-year periods with more than 25 landfalling major hurricanes, or more than a 100% increase of what has been observed over the past 4 years. 

Pielke, Jr. concludes: “Anyone who’d like to argue that the world is experiencing a ‘new normal’ with respect to tropical cyclones is simply mistaken.”

But, someone might say, 1970 roughly marks the advent of the “anthropocene,” the era in which fossil-fuel emissions start to mess up the climate; earlier eras had calmer weather. The Weinkle et al. study also contradicts that hypothesis. Pielke Jr. writes: 

There is even evidence in our paper (see our Figure 2) that the period before 1970 saw more intense hurricane landfalls than the period since. Older data from the North Atlantic and Western North Pacific (which together represents 64% of all global intense landfalling hurricanes 1970-2010 and 69% of all hurricanes) indicates that landfalling intense hurricanes in these two basins occurred at a 40% higher rate from 1950-1969 than 1970-2010. There were 9 intense landfalls in 1964 and 1965 in just these two basins, which equals the global record for all basins post-1970.



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