Is Recent Major Hurricane Activity Normal? Comment and Reply in Nature

The debate over whether there is an observable link between global warming and hurricanes rumbles on.

In this week’s Nature journal there is a comment and reply arising from Nyberg et al, Nature 447, 698-701 (7 June 2007):

Low Atlantic hurricane activity in the 1970s and 1980s compared to the past 270 years:

Hurricane activity in the North Atlantic Ocean has increased significantly since 1995 (refs 1, 2). This trend has been attributed to both anthropogenically induced climate change(3) and natural variability(1), but the primary cause remains uncertain. Changes in the frequency and intensity of hurricanes in the past can provide insights into the factors that influence hurricane activity, but reliable observations of hurricane activity in the North Atlantic only cover the past few decades(2). Here we construct a record of the frequency of major Atlantic hurricanes over the past 270 years using proxy records of vertical wind shear and sea surface temperature (the main controls on the formation of major hurricanes in this region1, 3, 4, 5) from corals and a marine sediment core. The record indicates that the average frequency of major hurricanes decreased gradually from the 1760s until the early 1990s, reaching anomalously low values during the 1970s and 1980s. Furthermore, the phase of enhanced hurricane activity since 1995 is not unusual compared to other periods of high hurricane activity in the record and thus appears to represent a recovery to normal hurricane activity, rather than a direct response to increasing sea surface temperature. Comparison of the record with a reconstruction of vertical wind shear indicates that variability in this parameter primarily controlled the frequency of major hurricanes in the Atlantic over the past 270 years, suggesting that changes in the magnitude of vertical wind shear will have a significant influence on future hurricane activity.

The comment is from Urs Neu: Is recent major hurricane activity normal?

The first paragraph reads:

Arising from: Nyberg et al. Nature 447, 698–701 (2007);

The anomaly of the recent increase in Atlantic major hurricane activity (MHA) is controversial. From a reconstruction of past MHA, Nyberg et al. conclude that the present activity is not unusual by comparison with that of the past 270 years. However, here I estimate the uncertainty of average MHA in the hurricane record before 1945 and show that the reconstruction of Nyberg et al. differs strongly from that record, and probably overestimates past MHA. Owing to this and further reasons, I question whether their reconstruction provides an accurate basis for conclusions about past MHA.

Nyberg et al reply:

Neu suggests that the reconstruction of Atlantic major hurricane activity (MHA) (that is, frequency) in Nyberg et al. overestimates past MHA because it differs significantly from the known observational records of tropical storms and MHA before 1945 and overestimates the influence of vertical windshear |Vz|.

Nyberg et al point out that:

“Neu’s record shows a sudden rise in MHA around 1944, coincident with the start of aircraft reconnaissance, which allowed much better monitoring of tropical cyclones. Also, according to ref. 4, the undercount bias is up to six tropical cyclones per year between 1851 and 1885, and up to four per year between 1886 and 1910. These biases are higher than the ones Neu(1) uses in his record of major hurricane numbers. Furthermore, to quote from ref. 4, ‘‘conclusions from this paper on the number of missed tropical cyclones are likely conservative’’. Moreover, MHA shows a stronger variability, closely correlated to [Vz](ref. 2), than tropical storms and non-major hurricanes in the reliable record(1–3), indicating a varying MHA/tropical storm ratio back in time.”

and conclude:

“The proxies used in ref. 2 reflect the region where almost all Atlantic major hurricanes form (see Fig. 2 of ref. 2), and the nonlinear solution(2) allows for varying MHAin response to [Vz] and other influences such as SSTs. Absolute MHA values may change slightly given different model calibrations, but the proxies(2) still indicate a declining trend in MHA until the early 1990s superimposed on decadal and multi-decadal variability and that the conclusions in Nyberg et al(2) remain.”

1. Neu, U. Is recent major hurricane activity normal? Nature 451, doi: 10.1038/
nature06576 (2008).
2. Nyberg, J. et al. Low Atlantic hurricane activity in the 1970s and 1980s compared to
the past 270 years. Nature 447, 698–701 (2007).
2. Best track data of the NOAA National Hurricane Center (HURDAT). Æhttp://
www.aoml.noaa.gov/hrd/hurdat/Data_Storm.htmlæ (data used as published 11 June
2007). (Hurricane Research Division, US National Oceanic and Atmospheric
Administration.)
4. Landsea, C. W. Counting Atlantic tropical cyclones back to 1900. Eos 18, 197–208
(2007).
5. Landsea, C. W. et al. in Hurricanes and Typhoons: Past, Present and Future (eds
Murname, R. J. & Liu, K.-B.) 177–221 (Columbia Univ. Press, New York, 2004).
6. Swanson, K. L. Impact of scaling behavior on tropical cyclone intensities. Geophys. Res.
Lett. 34, L18815 (2007).
7. Miller, D. L. et al. Tree-ring isotope records of tropical cyclone activity. Proc. Natl Acad.
Sci. USA 103, 14294–14297 (2006).
8. George, S. E. & Saunders, M. A. North Atlantic oscillation impact on tropical north
Atlantic winter atmospheric variability. Geophys. Res. Lett. 28, 1015–1018 (2001).
9. Aiyyer, A. R. & Thorncroft, T. Climatology of vertical wind shear over the tropical
Atlantic. J. Clim. 19, 2969–2983 (2006).
10. Giannini, A., Cane, M. A. & Kushnir, Y. Interdecadal changes in the ENSO
teleconnection to the Caribbean region and the North Atlantic Oscillation. J. Clim. 14,
2867–2879 (2001).
11. Jury, M., Malmgren, B. A. & Winter, A. Subregional precipitation climate of the
Caribbean and relationships with ENSO and NAO. J. Geophys. Res. 112, D16107
(2007).
12. Hoerling, M. P., Hurrell, J. W. & Xu, T. Tropical origins for recent North Atlantic
climate change. Science 292, 90–92 (2001).
13. Osborn, T. N. et al. Evaluation of the North Atlantic oscillation as simulated by a
coupled climate model. Clim. Dyn. 15, 685–702 (1999).

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UPDATE

FOR IMMEDIATE RELEASE – February 21, 2008

*** NEWS FROM NOAA ***
NATIONAL OCEANIC & ATMOSPHERIC ADMINISTRATION U. S. DEPARTMENT OF COMMERCE WASHINGTON, DC
Contact: Dennis Feltgen, NOAA 305-229-4404

Increased Hurricane Losses Due to More People, Wealth Along Coastlines, Not Stronger Storms, New Study Says
A team of scientists have found that the economic damages from hurricanes have increased in the U.S. over time due to greater population, infrastructure, and wealth on the U.S. coastlines, and not to any spike in the number or intensity of hurricanes.

“We found that although some decades were quieter and less damaging in the U.S. and others had more land-falling hurricanes and more damage, the economic costs of land-falling hurricanes have steadily increased over time,” said Chris Landsea, one of the researchers as well as the science and operations officer at NOAA’s National Hurricane Center in Miami. “There is nothing in the U.S. hurricane damage record that indicates global warming has caused a significant increase in destruction along our coasts.”

Full paper:

Normalized Hurricane Damage in the United States: 1900–2005

Roger A. Pielke Jr.1; Joel Gratz2; Christopher W. Landsea3; Douglas Collins4; Mark A. Saunders5; and
Rade Musulin6