Important New Paper on North Atlantic Hurricanes

A very important paper was published today by Chen et al. in the open-access journal Natural Hazards and Earth Systems Science (of the EGU) titled, "Quantifying changes of wind speed distributions in the historical record of Atlantic tropical cyclones" (PDF). The paper should go some way toward resolving disputes about the behavior of hurricanes in the North Atlantic, as it provides compelling evidence of a bias in the historical record due to observational practices. For instance, the paper finds that no Category 5 hurricane was observed in the North Atlantic until 1924, observing that "if the average frequency of Category 5 TCs during 1924–2008 were to be representative of the entire record, there should have been about 28 Category 5 TCs during the period 1851– 1923." The paper also provides (once again) strong confirming evidence supporting our work on the relative role of societal changes in the economic record of U.S. hurricane losses.

Here is an excerpt as related to that last point:

Focusing on the past six decades, we observe no sustained upward trends in wind speed distributions (Figs. 1 and 3), the mean wind speed at landfall or the annual frequency of occurrence of landfalling segments (Fig. 8). (Note that this annual frequency is specific to landfalling segments and different from the annual frequency of landfalling events since some events have multiple landfalling segments, e.g. in 2005 Hurricane Katrina made landfall in both South Florida and Louisiana.) This being the case, the dramatic increases in total economic and insured losses from TCs, which have been manifest over the past six decades, indicates that the increasing losses must be attributed to the factors other than wind speed alone. This is in accord with recent studies (Pielke, 2005; Pielke et al., 2008; Crompton and McAneney, 2008), which demonstrate the importance of demographic changes in driving the increasing economic cost of hurricane losses.

The paper concludes as follows:

The quality of observational data is central to the ongoing debate between a warming climate and consequences for TC frequency and intensities. Our analyses show clear, anomalous differences in the wind speed distributions between the early historical period and the very recent six decades. While these differences cannot unequivocally exclude a possible Global Climate Change cause, we suggest that data quality issues are more plausible.

An enormous challenge lies ahead for recovering reliable wind estimates in the early historical record, especially for highly dynamic and short-lived extreme TCs. The counting of events by Saffir-Simpson Hurricane categories is determined by threshold wind speeds, and if the wind estimates are themselves unreliable, how can derivative statistics be trusted sufficiently for long-term trend analysis? It is timely to recognise that using the early historical record will inevitably involve some irreducible uncertainties and “fixing” these may not be possible and that more physically-based models are needed to help resolve the data impasse. Conclusions drawn from scientific and insurance applications using the inherently lower-quality components of the record should be treated with caution.

Find the paper here in PDF.