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The recent extreme tropical storm Haiyan has brought the relationship between cyclones and climate change back into the newspaper headlines. This recent headline from Britain's Daily Mirror suggests the link is clear:

Typhoon Haiyan: As climate change continues, we should expect more devastating storms

The Guardian is a little more circumspect, but still believes the link is clear (my highlights):

As the devastating storm has only just happened, it is too soon for any research to have been done on whether global warming influenced typhoon Haiyan. But there are good reasons for expecting that it has (see below). Furthermore, the tools exist to determine how much climate change may have intensified the typhoon. They have already been used on other extreme weather events, giving a clear scientific answer that climate change had dramatically increased the risk of heatwaves and floods, for example.

The Economist strikes a note of caution, though, recognising that the theory isn't simple and the historic statistics are muddy (my highlights):

But the evidence so far is messy. Meteorological records are of uneven quality, and tropical storms vary widely in intensity, which makes spotting trends tricky ... The IPCC concludes that, although there is good evidence for more and stronger Atlantic hurricanes over the past 40 years, there is no consensus on the cause of them. Worldwide, there is no trend in either the frequency or the intensity of tropical storms.

Who is right? Theory hints that storms will get worse (but not in the simple way newspaper headlines imagine) but is that prediction backed by current meteorological statistics?

Note for clarification: the claim i'm interested in here is the one based on meteorological history. That is, is there a statistical trend in severity or frequency of storms?

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    The oceans warm more slowly. Are you asking whether there is evidence that current climate change has already caused more violent storms, or, are you asking whether future/continuing climate change will cause violent storms in future? – ChrisW Nov 17 '13 at 14:33
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    You don't need to demonstrate several claims in order to ask a question; but when you do reference different several claims (as above), it's better to be precise about what single question you are asking. – ChrisW Nov 17 '13 at 15:31
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    For example, if it's given that there's been a 0.1 degree rise in ocean temperature in the last century, are you asking whether such rise should show an already-statistically-noticeable increase in storms, as well as whether that increase has been seen? Or are you asking about the future? – ChrisW Nov 17 '13 at 15:38
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    The problem is that there are three claims there, and they're not mutually contradictory, nor are they mutually reinforcing. For example, it could be possible to increase the risk of heatwaves and floods, while decreasing the frequency and intensity of tropical storms. This question seems to have three distinct claims. Would you like to pick just one to be addressed here? – EnergyNumbers Nov 17 '13 at 19:15
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    A worthwhile question would be, given the estimated effect size (from the models) would we expect the observations to show a statistically significant trend over such a short time span? This is effectively a question of the statistical power of any test, which is essentially the flip-side of the coin of the level of statistical significance. As far as I can tell, the publications basically say that the physics suggests there will be an impact, but the effects are not statistically significant (yet). – Dikran Marsupial Nov 18 '13 at 10:24
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Scientists at the Geophysical Fluid Dynamics Laboratory, part of the US National Oceanic and Atmospheric Administration (NOAA) have determined that it's too early to tell.

Through research, GFDL scientists have concluded that it is premature to attribute past changes in hurricane activity to greenhouse warming, although simulated hurricanes tend to be more intense in a warmer climate.

Another page on the GFDL site indicates that we may be at the beginning of an increasing trend, but observations over a century-scale time period will be needed to clearly distinguish a trend from the natural variability.

There has been a very pronounced increase in the number of tropical storms and hurricanes in the Atlantic since the late-1980s. However, to gain insight on the influence of climate change on Atlantic tropical storm and hurricane frequency, we must focus on longer (> 100 yr) records of Atlantic hurricane activity since very strong year-to-year and decade-to-decade variability appears in records of Atlantic tropical cyclones.

Globally, the World Meteorological Organization published a statement in 2006 which noted that the 2004-2005 hurricane season was extremely active, with devastating storms around the world, but also noted that there is not yet a consensus on whether increased cyclone activity and intensity is caused by global warming.

Thus it is possible that global warming may have affected the 2004-2005 group of events as a whole. The possibility that greenhouse gas induced global warming may have already caused a substantial increase in some tropical cyclone indices has been raised (e.g. Mann and Emanuel, 2006), but no consensus has been reached on this issue.

  • If that is true of Atlantic-ocean hurricanes, is it also true of Pacific-ocean cyclones? – ChrisW Nov 17 '13 at 18:16
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    They are wise not to draw a conclusion from a couple of years. Take the Wikipedia list of the most intense tropical cyclones and consider those as strong as Typhoon Haiyan (895 hPa): 7 in the 1960s, 8 in the 1970s, 10 in the 1980s, 3 in the 1990s, 4 in the 2000s (of which 3 in 2004 or 2005), and 2 so far in the 2010s – Henry Nov 18 '13 at 0:49
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    I'm am not sure that in the topic of global warming, a government agency can be considered a reliable authority. – Ofir Nov 18 '13 at 16:09
  • The quote about the late-1980's is less helpful than the longer-term conclusion farther down the page: "Once an estimate for likely missing storms is accounted for the increase in tropical storms in the Atlantic since the late-19th Century is not distinguishable from no change." – joshuahedlund Jan 30 '14 at 22:19
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http://myweb.fsu.edu/jelsner/PDF/Research/ElsnerKossinJagger2008.pdf seems to indicate a likely relationship:

Atlantic tropical cyclones are getting stronger on average, with a 30-year trend that has been related to an increase in ocean temperatures over the Atlantic Ocean and elsewhere

[...]

Here we overcome these two limitations by examining trends in the upper quantiles of per-cyclone maximum wind speeds

[...]

We find significant upward trends [...] for the strongest cyclones. We note separate upward trends in the estimated lifetime-maximum wind speeds of the very strongest tropical cyclones (99th percentile) over each ocean basin, with the largest increase at this quantile occurring over the North Atlantic, although not all basins show statistically significant increases. Our results are qualitatively consistent with the hypothesis that as the seas warm, the ocean has more energy to convert to tropical cyclone wind.

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The short answer is that there is no significant trend, the operative word being significant. There is a cyclical trend, probably related to ENSO, but no trend that can reasonably be attributed to global warming. If anything, the data indicates that there might actually be a slight downward trend. But you are correct, the data is indeed muddy and as with statistics of any kind it can be massaged to produce a wide variety of results. Below are a series of links and graphs from a variety of sources that show no upward trend in worldwide cyclonic activity.

But it should be noted that Haiyan was not what it was cracked up to be. The maximum sustained wind speed were actually ~147 mph, based upon actual readings, making it a category 4 storm. Numerous category 5 storms have hit the Philippines in the past so as bad as Haiyan was it was not extraordinary. The higher wind speeds that were attributed to Haiyan were either estimates (check the footnotes) or the result of a mistake, based upon an early report that confused the storm’s 235 kph winds with 235 mph winds.

Also note that, in all the hype over Haiyan, little mention has been made of the dud that was the 2013 Atlantic hurricane season. NOAA had predicted an above-average hurricane season with 3-6 major hurricanes, but 2013 turned out to be one of the calmest years in recorded history. There was not a single major hurricane and the ACE (Accumulated Cyclone Energy) was a measly 29, the lowest in 30 years.

But what is the overall global trend in cyclonic frequency and power? Following is data from numerous sources showing, if anything, a slight downward trend.

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-13-00010.1

http://www.wunderground.com/hurricane/accumulated_cyclone_energy.asp?basin=gl

http://www1.ncdc.noaa.gov/pub/data/cmb/images/cei/step6.02-01.gif

http://www.aoml.noaa.gov/hrd/Landsea/gw_hurricanes/fig33.jpg

http://www.bom.gov.au/cyclone/images/tc-graph-1969-2012.png

http://policlimate.com/tropical/global_major_freq.png

http://coaps.fsu.edu/~maue/tropical/global_running_ace.jpg

  • Sorry, I have had to downvote this one as well for the "as with statistics of any kind it can be massaged to produce a wide variety of results.". This sort of accusation of dishonesty is unhelpful, and antithetical to true skepticism, which ought to be based instead on balanced analysis of the facts. In this case, as the tests for the trends is non-significant, it means that either there is unlikely to be a causal link, or that there are insufficient observations to draw a conclusion either way. Unless someone looks at the statistical power of the test, we can't rule out either option. – Dikran Marsupial Nov 20 '13 at 14:31
  • I'd be very happy to reverse my downvote if the answer is edited into a less provocative form. – Dikran Marsupial Nov 20 '13 at 14:33
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    Your downvote means nothing to me, Dikran. I'm not on this site to get gold stars. I am here to try to answer questions from a truly skeptical point of view. The fact that statistics can be massaged is neither provocative or antithetical to true skepticism, nor is it necessarily dishonest. It happens all the time, and it is used by both proponents and skeptics of AGW. What is antithetical to true skepticism is to ignore reality. – Bob Nov 20 '13 at 17:47
  • @bob I think Dikran is being a little harsh, but I think your answer would be improved by quoting examples and fleshing out the argument with some detail from the papers you link to (for example some block quotes validating the arguments you make). This is particularly important here if your argument is 'provocative' no matter how good your logic. – matt_black Nov 20 '13 at 21:49
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    [skeptics] The word so prominently displayed at the top of this page is, of course, a farce. You guys all knew it, but it took me a while to catch on. This site is as skeptical about AGW as in skepticalscience.com. In other words, it is "skeptical about global warming skepticism". I regret every second that I have wasted on this shill of a website. For some ignorance is bliss, so with my departure you can go back to breathing each others fumes and being blissful. – Bob Nov 21 '13 at 20:26

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