23 February 2010

Updated WMO Consensus Perspective on Tropical Cyclones

A team of researchers under the auspices of the World Meteorological Organization has published a new review paper in Nature Geoscience (PDF) updating consensus perspectives published in 1998 and 2006. The author team includes prominent scientists from either side of the "hurricane wars" of 2005-2006: Thomas R. Knutson, John L. McBride, Johnny Chan, Kerry Emanuel, Greg Holland, Chris Landsea, Isaac Held, James P. Kossin, A. K. Srivastava and Masato Sugi.

The paper reaches a number of interesting (but for those paying attention, ultimately unsurprising) conclusions. On North Atlantic hurricanes the paper states (emphasis added):
Hurricane counts (with no adjustments for possible missing cases) show a significant increase from the late 1800s to present, but do not have a significant trend from the 1850s or 1860s to present3. Other studies23 infer a substantial low-bias in early Atlantic tropical cyclone intensities (1851–1920), which, if corrected, would further reduce or possibly eliminate long-term increasing trends in basin-wide hurricane counts. Landfalling tropical storm and hurricane activity in the US shows no long-term increase (Fig. 2, orange series)20. Basin-wide major hurricane counts show a significant rising trend, but we judge these basin-wide data as unreliable for climate-trend estimation before aircraft reconnaissance in 1944.
The paper's conclusions about global trends might raise a few eyebrows.
In terms of global tropical cyclone frequency, it was concluded25 that there was no significant change in global tropical storm or hurricane numbers from 1970 to 2004, nor any significant change in hurricane numbers for any individual basin over that period, except for the Atlantic (discussed above). Landfall in various regions of East Asia26 during the past 60 years, and those in the Philippines27 during the past century, also do not show significant trends.
The paper acknowledges that the detection of a change in tropical cyclone frequency has yet to be achieved:
Thus, considering available observational studies, and after accounting for potential errors arising from past changes in observing capabilities, it remains uncertain whether past changes in tropical cyclone frequency have exceeded the variability expected through natural causes.
The paper states that projections of future activity favor a reduction in storm frequency coupled with and increase in average storm intensity, with large uncertainties:
These include our assessment that tropical cyclone frequency is likely to either decrease or remain essentially the same. Despite this lack of an increase in total storm count, we project that a future increase in the globally averaged frequency of the strongest tropical cyclones is more likely than not — a higher confidence level than possible at our previous assessment6.
Does the science allow detection of such expected changes in tropical cyclone intensity based on historical trends? The authors say no:
The short time period of the data does not allow any definitive statements regarding separation of anthropogenic changes from natural decadal variability or the existence of longer-term trends and possible links to greenhouse warming. Furthermore, intensity changes may result from a systematic change in storm duration, which is another route by which the storm environment can affect intensity that has not been studied extensively.

The intensity changes projected by various modelling studies of the effects of greenhouse-gas-induced warming (Supplementary Table S2) are small in the sense that detection of an intensity change of a magnitude consistent with model projections should be very unlikely at this time37,38, given data limitations and the large interannual variability relative to the projected changes. Uncertain relationships between tropical cyclones and internal climate variability, including factors related to the SST distribution, such as vertical wind shear, also reduce our ability to confidently attribute observed intensity changes to greenhouse warming. The most significant cyclone intensity increases are found for the Atlantic Ocean basin43, but the relative contributions to this increase from multidecadal variability44 (whether internal or aerosol forced) versus greenhouse-forced warming cannot yet be confidently determined.
What about more intense rainfall?
. . . a detectable change in tropical-cyclone-related rainfall has not been established by existing studies.
What about changes in location of storm formation, storm motion, lifetime and surge?
There is no conclusive evidence that any observed changes in tropical cyclone genesis, tracks, duration and surge flooding exceed the variability expected from natural causes.
Bottom line (emphasis added)?
. . . we cannot at this time conclusively identify anthropogenic signals in past tropical cyclone data.
The latest WMO statement should indicate definitively (and once again) that it is scientifically untenable to associate trends (i.e., in the past) in hurricane activity or damage to anthropogenic causes.


  1. At least they appear to be certain about the lack of a trend and our limited ability to predict future trends!

  2. I note that media coverage (that I've seen) focuses on the uncertain projections rather than the detection and attribution questions, which were the subject of the "hurricane wars" of 2005-2006. That debate has had a clear winner.

  3. I still have difficulties with the semantics employed in virtually all these types of papers.

    While they state:

    "...we cannot at this time conclusively identify anthropogenic signals in past tropical cyclone data."

    All the preceding verbage suggests there is no concusively about it. It simply can't be identified.

  4. The WMO statement is also interesting from another perspective. They come up with an agreed summary of the current literature on a narrow topic, and in a neutral, unpolitical environment. Essentially, they force the hand of the IPCC to say roughly the same thing.

    A model for things to come?

  5. You wouldn’t glean the above from the paper’s abstract, which paints alarming future predictions based on....yes, you’ve guessed it...computer modelling!

  6. Roger:

    If you send your post to Al Gore, please include your graphic to highlight also that Cuba does exist.

  7. See Seth Borenstein AP article: http://news.yahoo.com/s/ap/20100221/ap_on_sc/us_sci_warming_hurricanes

    Is he talking about the same paper???

  8. Maybe we are heading for a new world order.

    Working out the scientific basis and publishing those results.

    Instead of announcing the coming catastrophes and then finding a way to prop them up with "papers".

    It's very welcome.

  9. Comments regarding media coverage of this paper by Australian ABC can be found here including answers from one lead author to 13 questions about the paper.


  10. If Seth Borentein was referring to the same paper, he was certainly spinning like a top! Not surprising...

  11. I think the paper epitomizes the challenge that arises from language choice and approach, particularly by individuals who are firmly convinced that CAGW is alive & well, and coming to a storm near you (soon...even if not yet, and not in the past).

    The reason that Seth can "spin" the paper the way he has, is that the results of the modelling are presented with a certitude that is not their due. The following quote comes from the abstract to that self-same article:

    "However, future projections based on theory and high-resolution dynamical models consistently indicate that greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 2–11% by 2100. Existing modelling studies also consistently project decreases in the globally averaged frequency of tropical cyclones, by 6–34%. Balanced against this, higher resolution modelling studies typically project substantial increases in the frequency of the most intense cyclones, and increases of the order of 20% in the precipitation rate within 100|[nbsp]|km of the storm centre."

    So, these bad things shown in their models are destined to happen - apparently inevitably, if AGW is not reversed. Their models make it so...I would go on to make cynical comments about the connection between their language choice and their desire to secure further, future grant money, but it's too obvious to warrant the effort.

  12. Oh, and on extreme weather events, turn to the "Goracle", at http://www.repoweramerica.org/climate-change-causes-severe-weather/.

    Here's the link between extreme weather & CAGW made clear:

    "Arm yourself with facts and join Repower America in sharing the truth about climate change and extreme weather:

    Fact: Climate change causes more frequent and severe snowstorms
    Record snowstorms need two things: temperatures below freezing, and very high humidity. On a planet warmer by a few degrees on average, the Northeast US will still have plenty of days below freezing; the big difference will be warmer seas producing higher levels of moisture in the air — and therefore more severe cold-season storms.

    Fact: We can expect more extreme weather
    Scientists tell us that climate change has already led to more extreme weather in the United States and we can expect stronger hurricanes, more wildfires, heatwaves and droughts, to name a few. The cost of inaction could reach half a trillion dollars a year.

    Fact: The world is warming at a quickening pace
    Weather in one region over days or months should not be confused with climate or the patterns of weather over decades and centuries. And the science is clear here: the last decade was the hottest on record. And to put this year’s weather in perspective, January was warmer than average for the continental United States."

    Sigh...(h/t to Anthony Watts)

  13. An interesting tidbit in Seth's article (he clearly didn't as Roger his views on this), regarding whether the IPCC report had accurately reflected the state of the research 2006:

    "In 2007, the authoritative Intergovernmental Panel on Climate Change said it was "more likely than not" that man-made greenhouse gases had already altered storm activity, but the authors of the new paper said more recent evidence muddies the issue.

    "The evidence is not strong enough that we could make some kind of statement" along those lines, Knutson said. It doesn't mean the IPCC report was wrong; it was just based on science done by 2006 and recent research has changed a bit, said Knutson and the other researchers.

    Lately, the IPCC series of reports on warming has been criticized for errors. Emanuel said the international climate panel gave "an accurate summary of science that existed at that point."

    Maybe Mr. Knutson needs to review the research a bit more closely...(and the IPCC's claims, and they way they were (not) substantiated.

  14. Yet again the frequency of severe storms is projected to reduce by a significant amount. Think anyone will remember that?

    But there are a couple of problems with the modeling effort which Knutson is obviously well aware of:

    a) Vecchi and Sodens work:
    that using relative SST as a predictor rather than absolute SST gives no projected increase in hurricane strength. While acknowledged, this view has clearly been largely ignored for projection purposes.

    b) The global models used for downscaling are well known to be utterly inadequate for regional temperature forecasting and they are even sitting on the lowest bound of the predicted IPCC error margin for global temperatures.

    So the two fundamental assumptions of the modeling exercise are built on quicksand. You'd have to have an agenda not to acknowledge that with these huge potential biases the projections are practically worthless. Instead they are given pride of place.

    Since potential differences rather than absolute values drive every other storm, the relative SST predictor, which accords with the historical data, would be my predictor; a repeat of what I wrote on the nature blog before the Vecchi paper even came out.

  15. Update Tom Knutson responds to ABC NEWS WATCH QUESTIONS...see here


  16. I don't understand the wording:
    "...we cannot at this time conclusively identify anthropogenic signals in past tropical cyclone data."
    Why do they say "at this time"? Are they suggesting that, in the future, with who knows which procedures applied to the same data we have now (a.k.a. data massaging), an anthropogenic signal may be identified? There is no signal, period. If a signal is identified in the future, it will be using data from the future. There is no signal in today's past data. There is no trend between 1850 and today, and nothing they do can change that.

  17. re: ABC NEWS WATCH
    I particularly like the comment "with changes of up to ±50% or more projected by various models."

    Well I don't think anyone will be buying that product!

    And the main conclusion though is "The remarkably consistent result of a projected reduction in global TC frequency across a range of different modeling studies"

    So good news? The only thing they are sure about is that there will be a decrease in storms. All the rest is a coin toss. Not exactly how it was spun is it?

  18. And the hurricane insurance refunds will be mailed when?

  19. This is from Knudsen's own web page.

    It is premature to conclude that human activity--and particularly greenhouse warming--has already had a detectable impact on Atlantic hurricane activity. However, human activity may have already caused substantial changes that are either below the 'detection threshhold' or are not properly modeled yet (e.g., aerosol effects).

    Anthropogenic warming over the next century will likely cause Atlantic hurricanes to be more intense (by a few percent on average) and have substantially higher rainfall rates than present-day hurricanes.

    Anthropogenic warming over the next century more likely than not will lead to greater numbers of very intense Atlantic hurricanes, despite a decrease in the overall numbers of hurricanes.

    Look, you can try to find reasons to deny AGW/ACC, but Knudsen's not your go-to guy. Sorry. He still supports AGW/ACC.