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Hurricanes And Climate Change: Boy Is This Science Not Settled!
Posted on 3 September 2010 by gpwayne The current research into the effects of climate change on tropical storms demonstrates not only the virtues and transparency of the scientific method at work, but rebuts the frequent suggestion that scientists fit their findings to a pre-determined agenda in support of climate change. In the case of storm frequency, there is no consensus and reputable scientists have two diametrically opposed theories about increasing frequencies of such events. The background to these enquiries stems from a simple observation: extra heat in the air or the oceans is a form of energy, and storms are driven by such energy. What we do not know is whether we might see more storms as a result of extra energy or, as other researchers believe, the storms may grow more intense, but the number might actually diminish. What do the records show? According to the Pew Centre, “Globally, there is an average of about 90 tropical storms a year”. The IPCC AR4 report (2007) says regarding global tropical storms: "There is no clear trend in the annual numbers [i.e. frequency] of tropical cyclones." But this graph, also from the Pew Centre, shows a 40% increase in North Atlantic tropical storms over the historic maximum of the mid-1950, which at the time was considered extreme: 
But while the numbers are not contested, their significance most certainly is. Another study considered how this information was being collected, and research suggested that the increase in reported storms was due to improved monitoring rather than more storms actually taking place. And to cap it off, two recent peer-reviewed studies completely contradict each other. One paper predicts considerably more storms due to global warming. Another paper suggests the exact opposite – that there will be fewer storms in the future. What can we conclude from these studies? About hurricane frequency – not much; the jury is out, as they say. About climate change, we can say that these differing approaches are the very stuff of good science, and the science clearly isn’t settled! It is also obvious that researchers are not shying away from refuting associations with climate change, so we can assume they don’t think their funding or salaries are jeopardised by research they believe fails to support the case for AGW. The scientific method is alive and well. Never mind the frequency, feel the width So far, all we’ve managed is to document here is what we don’t know for sure yet. But we do know there is extra energy in the system now, so could it have any other effects on tropical storms? Here, the science is far less equivocal, and there is a broad consensus that storms are increasing in strength, or severity. This attribute, called the Power Dissipation Index, measures the duration and intensity (wind speed) of storms, and research has found that since the mid-1970s, there has been an increase in the energy of storms. Recent research has shown that we are experiencing more storms with higher wind speeds, and these storms will be more destructive, last longer and make landfall more frequently than in the past. Because this phenomenon is strongly associated with sea surface temperatures, it is reasonable to suggest a strong probability that the increase in storm intensity and climate change are linked. This post is the Basic version (written by Graham Wayne) of the skeptic argument "Hurricanes aren't linked to global warming".  0  0
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Heh. I wasn't referring to you, or to anyone else in particular. I was just using that as an example of the kind of remark that tends to hinder rather than promote useful discussions.
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ProfMandia ,
Thanks for the link to the paper I can see their reasoning now and it seems sound .
It surprises me that results of papers like these are not discussed more in the general media as they are quite dire examples of what could be in store for the world .
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Whilst hurricane intensity in the US may be of interest to Americans, the US is only some 2% of the Earth's surface, and most of us aren't Americans.
What happens if we look at the tropics?, an area making up roughly 25% of the Earth's surface and inhabited by some 40% of the world's population?. It is the region where hurricanes/cyclones form after all.
Increasing destructiveness of tropical cyclones over the past 30 years
Emanuel 2005
"Whatever the cause, the near doubling of power dissipation over the period of record should be a matter of some concern, as it is a measure of the destructive potential of tropical cyclones.Moreover, if upper ocean mixing by tropical cyclones is an important contributor to the thermohaline circulation, as hypothesized by the author, then global warming should result in an increase in the circulation and therefore an increase in oceanic enthalpy transport from the tropics to higher latitudes."
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Nice work Graham. As with so much else in climate change the burden of proof argument has come to fall the wrong way. If deniers are really going to argue that frequency and/or strength of hurricanes is NOT going to increase with rising temperatures, it should be up to them to explain why this would be the case. I can see no good reason why both intensity and frequency would not increase. Given that hurricanes always occurred with lower temperatures, it is nonsense to suggest that, once given the conditions to start, greater warmth wouldn't, on average, leader to a greater intensity. It also seems to me intuitively obvious that warmer moister air columns are going to be more frequently available to trigger initial hurricane formation.
The graphs that Graham and Dappled Water show exactly coincides with others showing the rise in CO2 levels and the resultant effects, beginning around the mid 1970s. Either we are faced with the most astonishing and inexplicable series of coincidences or all of these graphs show the consequences of climate change.
And l we also have in this thread, yet agin, the use of figures from the US to try to disprove some obvious outcome of global warming. And even then, whatever else BPs graph shows, it concurs in the recent increase in activity.
In thread after thread we are it seems to keep forever being asked to prove that one plus one equals two.
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BP, you have successfully demonstrated that really bad hurricanes/cyclones have a tendency not to travel to the United States, but given that they're not actually born there, not really enlightening.
There's actually peer reviewed studies (see @34) that there are more intense hurricanes/cyclones being generated in the last few decades in the tropical regions. So it appears they have a hunkering for more international travel. The PDI kinda looks like a hockey stick too.
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My understanding is that much of the uncertainty about whether AGW will lead to more frequent tropical storms is due to the competing effects of SST and wind shear, both of which will presumably be increased in a warmer world. Higher SSTs tend to promote TS development but higher wind shear tends to hinder it. Thus, different models that emphasize one parameter or the other will give very different results in terms of future TS frequency.
See, for example:
Knutson et al., 2008. Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions. Nature Geoscience 1: 359-364.
Zhao et al., 2008. Simulations of Global Hurricane Climatology, Interannual Variability, and Response to Global Warming Using a 50-km Resolution GCM. J. Climate, 22, 6653–6678.
Knutson et al., 2010. Tropical cyclones and climate change. Nature Geoscience, 3, 157 - 163.
The latter is somewhat interesting -- it's a review article, with a list of authors covering the gamut from Chris Landsea to Kerry Emanuel. It also nicely illustrates that some parts of this picture seem clear, while others are still very uncertain:
Whether the characteristics of tropical cyclones have changed or will change in a warming climate — and if so, how — has been the subject of considerable investigation, often with conflicting results. Large amplitude fluctuations in the frequency and intensity of tropical cyclones greatly complicate both the detection of long-term trends and their attribution to rising levels of atmospheric greenhouse gases. Trend detection is further impeded by substantial limitations in the availability and quality of global historical records of tropical cyclones. Therefore, it remains uncertain whether past changes in tropical cyclone activity have exceeded the variability expected from natural causes. 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 km of the storm centre. For all cyclone parameters, projected changes for individual basins show large variations between different modelling studies.
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Ned, that's an interesting quote. If true would it mean that the whole discussion (about evidence on stronger or more frequent cyclones already being visible in the records) is a straw man because noticeable changes would only appear in the second half of this century?
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I don't know if it has been raised before or not in other threads, but it should be considered as part of the discussion how such events rather than being considered indicators instead form part of a negative feedback system.
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@Berényi Péter: Why are you drawing a linear trend line on your graphs? They clearly do not represent linear processes. One could argue for a multi-decadal signal in your 25-year averaging, and probably in your 10-year averaging. On what basis did you choose your averaging periods?
If you want to do something interesting, integrate your data over each solar cycle and express the results in terms of energy released.
BTW, what does "Annual Sum of Saffir-Simpson Category" mean? For 2004 there were 9 hurricanes in the Atlantic giving an annual sum of Saffir-Simpson categories of 27, well above the range of your scale.
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I think it is....NOAA
intensity-or-frequency
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Thanks for all the comments. A few responses:
HumanityRules: you were right - Holland and Landsea.
Berényi Péter: As mentioned in the post, models predict a reduction in frequence but increase in energy. This will lead to greater landfall if correct.
Dappledwater: nice one.
David Horton: Thank you. I quite agree - it is strange how the burden has been shifted. More energy into a system must have an effect, and if the effect isn't the obvious one (or the slightly less obvious but logical PDI increase) it is encumbent on those promoting the disssent to validate it with data.
Ned: so, to sum up then - nobody's got a bloody clue! :)
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An interesting graphic of 150 years of tropical storm tracks, clear to see which region gets hammered the most.
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gpwayne @ 42 - "As mentioned in the post, models predict a reduction in frequence but increase in energy. This will lead to greater landfall if correct."
Is that true?. The graphic above, indicates the more intense hurricanes seem to have less likelihood of making landfall (well major land masses anyway). Granted, it's only "eyeballing" & I've only skimmed through a handful of papers so far.
0 0 Moderator Response: [Graham] - check out the intermediate, the paper is referenced there. (As I understand it, the argument is that greater intensity will lead to increased duration, so more will make landfall before blowing themselves out).
Living in Florida as I do it is clear that the Pew Center's plot of hurricanes is a case of torturing the data to suit an agenda.
Thank you Berenyi Peter (#16 & #27) for injecting some facts into the discussion.
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I noticed that the Pew graph used ALL the available data from the north atlantic. BP's US landfall graph probably uses 5% of the data, (or less). This relates to John Cook's mantra that we need to look at all the data and not just one litle piece. You can look at 5% and say that you see no pattern, only noise. Or you can look at the whole picture.
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I thought Ryan Maue's website might be useful for the discussion.
The final section in Graham's article "Never mind the frequency, feel the width" worries me.
What seemed to be the most recent concensus was summed up in a Nature paper earlier this year. It was authored by most of the personalities involved in the debate and seems to have come to the conclusion that we can not yet distinguish any anthropogenic signal in the hurricane data. They remain certain of future predictions. So Graham's comments should really be in the future tense rather than the present tense. Any suggestion that the recent increase in any hurricane metric is anything but part of the natural variability is wrong.
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michael sweet (#46)
Amen to the idea of using all the data. I totally support John Cook on that one.
When it comes to selecting surface weather stations for inclusion in HADCRUT3, GHCN and NOAA/GISS databases the same idea should apply. Yet this excellent website seems to meekly accept that over 80% of the available stations have been discarded since 1975. See:
http://www.skepticalscience.com/Station-drop-off-How-many-thermometers-do-you-need-to-take-a-temperature.html
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GC - the article you cite shows that dropping the stations doesnt produce a warming bias. However, your post implies that you think that wicked scientists are willfully holding back data that they should be using. However the data isnt in their hands to withhold. To quote NCDC.
"The reasons why the number of stations in GHCN drop off in recent years are because some of GHCN’s source datasets are retroactive data compilations (e.g., World Weather Records) and other data sources were created or exchanged years ago. Only three data sources
are available in near-real time. The rise in maximum and minimum temperature stations and grid boxes in 1995 and 1996 is due to the World Meteorological Organization’s initiation of international exchange of monthly CLIMAT maximum and minimum temperature
data over the Global Telecommunications System in November 1994." (Source here
Of course nothing that a willingness to pay more tax on your part to support these data collations wouldn't fix...
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GC, my comment on that more relevant thread complements scaddenp's comment that he has correctly put on that other thread.
Gee, it seems you've made that same contention on that other thread earlier, and were given the same information in return. But you never responded and now are repeating the same contention.
0 0 Moderator Response: Everybody please follow scaddenp's example by continuing this discussion on that other thread.
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There is a recent rise indeed, but it's a far cry from being unprecedented. More like a recovery, even if it is a bit fainter than the scary surge around 1880.
See The Deadliest, Costliest, and Most Intense United States Tropical Cyclones From 1851 to 2006 from NOAA National Hurricane Center.
BTW, there are only three category 5 hurricanes on record that made landfall in the US.
1935 "Labor Day"
1969 Camille
1992 Andrew
Years with category 4 storms: 1856, 1886, 1893, 1898, 1900, 1915(2), 1919, 1926, 1928, 1932, 1947, 1954, 1957, 1960, 1961, 1989 and 2004. Again, no increasing frequency is seen.
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