Climate Feedback

Hurricane peak in the past

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Whether climate change will increase the number of hurricanes is fiercely debated in the research community. There is also strong disagreement between researchers over the accuracy of claims that hurricane activity has peaked over the past ten years.

But a new study in Nature this week (subscription) throws more weight behind arguments that hurricane numbers are on the rise and could continue to surge as a result of global warming. The paper’s covered here on Nature News.

The study looked at historical hurricane activity across the entire tropical Atlantic basin to see if the current peak in storm numbers is anomalous. It found that it was not. The results show high hurricane activity also occurred at around 1000 AD, where levels approached that seen today.

Previous research has shown that warm sea surface temperatures could encourage hurricanes to form. Michael Mann, a climate scientist at Pennsylvania State University and the study’s lead author, says the historical peak in hurricane activity coincided with periods of high sea surface temperatures. This suggests that the annual number of hurricanes will continue to increase as a result of global warming, says Mann.

“This tells us that the relationship between sea surface temperatures and cyclone activity seems to be robust and gives support to the debate that we are likely to see an increase in tropical cyclone activity in response to global warming,” he says.

But given the passion with which the scientific community is divided on this issue, it’s unlikely we’ve heard the last of this.

Natasha Gilbert

Image: NASA

Comments

  1. Report this comment

    Roger Pielke, Jr. said:

    https://rogerpielkejr.blogspot.com/2009/08/changing-perilous-assumptions-to-suit.html

    In 2007 Michael Mann and colleagues published a paper (PDF) critical of work suggesting an undercount in storms from historical records, claiming that it was “perilous” to assume that there is a “fixed” relationship between landfalling and total hurricanes in the Atlantic basin:

    “Of course, estimation of undercount based on the assumption of a fixed relationship between total TC counts and the number of landfalling storms is perilous. Such an approach assumes, in particular, that the large-scale atmospheric steering which determines the trajectories of TCs once they’ve formed is constant, when there is in fact strong evidence that it is highly variable over time . . .”

    Now Mann and another set of colleagues (PDF) make what appears to be the exact opposite assumption in a paper just out in Nature, that landfalls are “in rough proportion” to overall basin activity:

    “We compared the sediment-based record against the above statistical estimate of basin-wide tropical cyclone activity (Fig. 3), guided by a working assumption that an appropriately weighted composite of regional landfalling hurricane activity varies, at multidecadal and longer timescales, in rough proportion to basin-wide tropical cyclone activity.”

    What is troubling is that the analysis in the second paper depends to some degree upon the first (that is, if there is a significant undercount, which Mann dismisses, then the nature of the relationships used in the second paper changes). I note that the recent paper shows a dramatic uptick in storm activity that has been convincingly refuted by “strong evidence that there has been no systematic change in the number of north Atlantic tropical cyclones during the 20th century.” It would be interesting to see Mann’s analysis run with observational data properly adjusted for undercount and short-duration storms, or at a minimum considering these factors as part of the uncertainties in the analysis.

    At the minimum, the two Mann et al. studies rely on highly inconsistent assumptions, yet one analysis depends upon the other. Not good.

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    JohnAnnArbor said:

    If the storm of 1703, a hurricane which hit Great Britain at full force, were repeated today, would it be attributed to global warming? I think it’s a fair question, as often various weather phenomena we see today are labeled “unprecedented” even though historical records show that extraordinary weather events have occurred sporadically throughout recorded history.

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    Dean Rowe said:

    Roger Pielke, Jr.:

    Of course, estimation of undercount based on the assumption of a fixed relationship between total TC counts and the number of landfalling storms is perilous. Such an approach assumes, in particular, that the large-scale atmospheric steering which determines the trajectories of TCs once they’ve formed is constant, when there is in fact strong evidence that it is highly variable over time . . .

    Now Mann and another set of colleagues (PDF) make what appears to be the exact opposite assumption in a paper just out in Nature, that landfalls are “in rough proportion” to overall basin activity:"

    I looked at both Mann papers and I don’t see this “exact opposite assumption”. In the second paper, when they say landfalls are “in rough proportion” what they wrote was

    …guided by a working assumption that an appropriately weighted composite of regional landfalling hurricane activity varies, at multidecadal and longer timescales, in rough proportion to basin-wide tropical cyclone activity.

    (emphasis added)

    This to me clearly shows that they did not assume a “fixed relationship” but rather a variation “at multidecadal and longer timescales”

    What is troubling is that the analysis in the second paper depends to some degree upon the first (that is, if there is a significant undercount, which Mann dismisses, then the nature of the relationships used in the second paper changes).

    Here’s where they cite the previous paper:

    The tropical cyclone count

    series was first corrected for a modest estimated undercount3 [the previous Mann paper] before the midtwentieth-century undercount, although similar results were obtained (Supplementary Information) using the largest2,29 published estimates of undercount

    bias.

    That looks like Mann didn’t just dismiss significant undercounts, but rather they don’t seem to make as big a difference as you implied.

    So, while the second paper does reference the first, I don’t see that the second hinges substantially on the first. The second paper also looks to use the same assumptions of the first (by using the same “modest” undercount), not the opposite.

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    keith said:

    Hurricanes and earthquakes have really banged the third world countries in past 5 years.

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