The Atlantic hurricane season will soon be upon us again , and no doubt many people will recall last year’s devastating Hurricanes that swept across Florida. There was a great deal of press about these storms, as 3 major hurricanes and 5 tropical storms made landfall in the US. According to HurricaneProtection.com, the last time eight different tropical cyclones impacted the United States coastline in a single season was 1916. There were a total of 15 tropical storms and hurricanes, which means that the total number of storms that year was higher than 95% of the previous years of hurricane observations. There was also a record number of Typhoons over Japan in 2004 (10! The previous record was 6 from 1996) . Typhoons are the same as Hurricanes, but have a different name over the Indian ocean and the western Pacific. They are also known as ‘tropical cyclones’. Furthermore, it was the first time that a tropical cyclone had been observed in the south Atlantic (see WMO Climate News, Jan 2005, p. 12)! So, what’s going on?
The topic regarding tropical storms have also been a contriversial topic in the scientific community. Has there really been a systematic long-term trend in the storm statistics? Chan and Liu (2004) found no systematic change in typhoons that could be related to changes in the sea surface temperature. Because trends in sea surface temperature (SST) have been relative weak over the past 50 years, Knutson & Tuleya (2004) have argued that CO2-induced tropical cyclone intensity changes are unlikely to be detectable in historical observations and will probably not be detectable for decades to come. Although there is no clear linear trend in the Atlantic hurricane number (see Fig. 1), there may nevertheless be other indications which may suggest that the tropical cyclone statistics are changing.
Fig.1: Number of storms every 5-year interval since 1850 divided in 6 different categories of severities, with ‘Tropical Storm’ as the least and ‘Category 5’ as the most powerful cyclones. The whole column indicates the total number of tropical cyclones over the given 5-year interval.
We know for sure that the number of Atlantic cyclones is affected by the presence El Ninos (the frequency is almost halved) and La Ninas (many hurricanes). Hence, we know that there must at least be something that influences the hurricane statistics. We know that one necessary condition for Atlantic cyclones to be spawned is that the sea surface in parts of the tropical Atlantic must be higher than a threshold value (~27deg C). The state of the atmosphere must also be favourable, that is, the winds should not change too much with height, as a wind shear might ‘tear’ the growing structures.
GCMs tend to be too coarse to resolve cyclones, but high-resolution regional models for storm studies exist. Knutson & Tuleya (2004) have studied how the hurricane activity may respond to increased CO2 levels, given known physical laws, and found a deepening of the central pressure and more intensive rainfall. If we choose to look at other statistics from the same data as in Fig. 1 – say the maximum wind speeds or minimum pressure associated with the Atlantic hurricanes – there appears to have been a trend after all (Fig. 2).
Fig.2: Indications of maximum wind speed and minimum pressure of the most severe tropical storm per season.
The analysis in Fig. 2 indicates a systematic tendency where the strongest winds associated with tropical storms have been in the most recent decades. The graphic also shows a deepening of the minimum pressure over time, i.e. an indication of increased severity – at least if the data represents what actually happened in the past. This trend is consistent with the model results of Knutson & Tuleya (2004) and with a recent statement made by Trenberth, disputed by Chris Landsea. On the one hand, the data presented in Fig. 2 seem to speak for themselves, suggesting there has been a trend in cyclone severity. Fig. 1, on the other hand, suggests there is little indication of a trend. The impression we get from the two figures seem to be contradicting, and we should rightly ask: Are the data consistent, and is their quality reliable? Before 1950, the data is scarce, especially with respect to pressure observations. The wind data is probably less accurate in the early part of the record also. Question is, was there a trend before 1950, or were the minimum pressure values more stable then?
In an independent study, Gettleman et al. (2002) noted a 0.4 degC/decade trend in the dew-point temperature in the 1958-1997 radiosonde observations from the Tropics. They found indications that the Convective Available Potential Energy (CAPE) may have increased. The CAPE and dew-point temperature are independent measurements that can give us clues about cyclone trends, but they are also a potential indicator of climate change.
World-wide trends?
The media attention on tropical cyclones was not been limited to the U.S., south Atlantic or Japan. Australia, has recently been ravished by Tropical Cyclone Ingrid, which was “unusual in that it is the only cyclone in recorded history to impact, as a severe tropical cyclone, on the coastline of three different States or Territories”.
Other storms
The issue of storm trends and global warming has also received attention in Europe. A fairly recent devastating storm over Fance (December 26-27, 1999) made the headlines. Mid-latitude storms, such as those sweeping over western Europe, are distinct to tropical cyclones (more about this later). Some researchers have found that the frequency of mid-latitude storms may have dropped slightly over the European continent, but there have also been indications that the frequency of storms has increased elsewhere (the North Atlantic storm track – Iceland/Norwegian sea). Geng & Sugi (2001) noted an upward trend in the number of North Atlantic storms, albeit with strong decade-to-decade variations. The storm activity around Scandinavia during the most recent winter (2004-2005) was unusually high, and there was a great deal of media attention on the storm trains. These systems were responsible for a mild winter over northern Europe for most of the winter (in fact, March was colder than the other winter months, which is unusual) as well as extensive damage in southern Sweden.
Theoretical considerations
Why do we think that tropical cyclones would change because of a global warming? We have some basic physics-based principles that may possibly provide some insight. The main driving mechanism for all storms is the condensation of water vapour releasing energy/heat. Temperature differences cause instabilities and drive winds, and unstable disturbances grow into powerful storms. Tropical cyclones differ from mid-latitude storms in their primary driving mechanism. So-called ‘baroclinic instabilities’ are more important for the mid-latitude storms, whereas plain convective instabilities are the primary cause for the tropical cyclones – such as an increase in the CAPE.
Some climate models suggest that a global warming may be favourable for more intense mid-latitude storms. There are also a couple of physics-based considerations that can provide an indication of the main features: (i) As the surface and atmosphere warm up, more energy (heat) becomes available in the form of water vapour (more evaporation and the air manage to hold more moisture), but (ii) one factor which may act as a moderating influence, is that a global warming is expected to warm the polar regions faster than the lower latitudes, hence reducing the meridional (north-south) temperature differences (gradient). Mid-latitude storms tend to form where there are sharp temperature gradients, where conditions for instabilities are favourable. There tend to be a sharp temperature drop poleward of the polar fronts, and it is no coincidence that this is the same regions where the storm tracks lie. The mid-latitude storms play an important role in the climate system, as they facilitate the poleward heat transport. Hence, we would expect to see a relationship between the number of storms and the pole-equator temperature differences. Perhaps part of the reason why the poles warm more strongly than the lower latitudes (in addition to reduced sea-ice) may be an increase in storm activity along the storm tracks?
If the present high frequency of tropical cyclones prevails, that in itself would be a climate change per definition (i.e. a change in cyclone statistics). It is (virtually) impossible to prove that a single (or a small number) freak weather event(s) is (are) caused by increasing CO2, but when a large number are observed, it may be possible to spot a pattern of change – yet it is difficult to attribute such a change to a cause unless the mechanisms are understood. So, we can only tell for sure with hindsight whether the high number of tropical cyclones are an indication of a climate change (let’s hope it’s not!). It is nevertheless legitimate to ask whether these have been a consequence of natural variations of if a global warming can have increased the risk for more intense storms – and many have done so (e.g. in Eos 2004). And rightly so – when there are emerging signs that can point to a change in the storm statistics, there ought to be a discussion about these results. In my opinion, a disagreement between experts at present stage on this issue is therefore part of the normal scientific discourse.
Technicalities
For the sake of transparency and reproducability – two pillars of science -, the figures presented here are derived through an analysis using the R-script hurricanes.R. It is important to note that the analysis presented here is based on the re-analysis data from NOAA Hurricane Research Center, which has been taken at face value, and that it is indeed important to know the limitation of the data. For instance, the accuracy of the data may be less in the early period due to less observations at the early stage.
References:
Geng & Sugi (2001), Variability of the North Atlantic Cyclone Activity in Winter Analyzed from NCEP-NCAR Reanalysis data, J. Clim., 14, 3863-3873
Knutson & Tuleya (2004) Impact of CO2-Induced Warming on Simulated Hurricane Intensity and Precipitation: Sensitivity to the Choice of Climate Model and Convective Parameterization, J. Clim. 17, 3477-3495
Gettleman et al. (2002), Multidecadal trends in tropical convective available potential energy, JGR, doi:10.1029/2001JD001082
Chan & Liu (2004) Global Warming and Western North Pacific Typhoon Activity from an Observational Perspective, J. Clim. 17, 4590-4602
re: “We know for sure that the number of Atlantic cyclones is affected by the presence El Ninos (the frequency is almost halved) and La Ninas (many hurricanes).” is author suggesting MORE El Ninos would lessen cyclones, but more La Ninas increase hurricanes?: why??: isnt la nina just a little el nino??
[Response:
La Ninas are not ‘little El Ninos’. El Nino is characterised by warmer than normal sea surface along the equator in the eastern Pacific, whereas La Nina is colder than normal conditions over the same region. El Nino and La Nina can be regarded as opposites. More on El Nino & La Nina on
http://www.pmel.noaa.gov/tao/elnino/nino-home.html
Furthermore, the above stated relationship is valid for Atlantic & Carribian hurricanes. In the Pacific, there is another relationship. -rasmus]
You say
“the last time eight different tropical cyclones impacted the United States coastline in a single season was 1916. ”
What caused the increased number of tropical cyclones in 1916 when ther was not yet signs of global warming
[Response:We know that these things also have a random character like the weather in general – sometimes there are more and sometimes there are fewer, just like it sometimes rains heavily and sometimes lightly. The question is, of course, if the weather statistics – i.e. climate – changes. -rasmus]
re: #2. Whether tropical cyclones impact the US is not a function of the number of cyclones altogether. Rather it is more a function of the general circulation pattern that year. Hurricane Andrew in 1992 was a catastrophic storm for south Florida yet it was really the only storm of major significance that year. I beleive 1995 (could be off a year or two) was an extremely active year for Atlantic hurricanes but not so much for landfalling storms. Last year the circulation pattern was such that a large trough over the eastern US enhanced the path of cyclones into Florida. It is possible the same held true in 1916. That is not a global warming issue.
Can the data be analyzed by comparing storm frequency (and other properties) at roughly the same stage of the El Nino/La Nina cycle across time, sort of like taking the annual cycle out of temperature anomoly data? If so, does this make anything clearer?
[Response:You could try it – pick up the R-script from the link at the bottom. The script finds the data at the right URL, and you can explore the data… -rasmus]
One of the aspects of “global warming ” that makes it appear so disreputable to some is the willingness for those who speak for it to do so in alarming, albeit false tones. Every climate record is “more evidence”; Kilamanjaro’s lack of snow is now “another sign”. Of course weather records are limitless in number and it’s therefore quite unsurprising that new climate records are set every day as they always have been. The climate is now said to be “more changable” or “more erratic” or “more damaging” etc. These are qualitative judgements which have no meaning in science. Indeed is there even a unit of measurement for climate volitility?
It always surpises me when people interested in a dispassionate search for truth allow these characterizations to go on unchecked by any call for more reasoned discourse on the part of climate researchers. When the New York Times spreads headlines over “more costly hurricanes” as evidence of “global warming; whrere is the sane voice that scolds them for advancing such preposterous sylogisms.
[Response:I hope you do not imply that we spreak with false tones here at RC. I know that media tend to make the headlines scream at you in order for you to buy their papers or tune in, but the piece here used factual events to frame the question if the storms are affected by a global warming. -rasmus]
I invite posters here to read a bio electrical description of tropical storms and its relation to rising CO2 at TWC bb:
http://www.weather.com/interact
Go to tropics thread.
For the Fig 1, why include tropical storms in a hurricane severity graph, since by definition they arent Hurricanes at all. Is this an example of padding data.
What would the secondary grey line indicate, is it meant to be some sort of statistical analysis
[Response:You are right, but since there are more weaker storms than intense storms (larger sample gives more robust statistics), it’s also interesting to look at them to see if they are changing. Tropical storms can be fairly mighty too… The second grey line gives an indication of the ratio intense (category 3 and higher) to weak cyclones. -rasmus]
Disney, the Fall of an Empire — A short story by John M. Crichton III
Time: September 27, 2105; Place: Orlando Island, off the SE coast of NCSA; Scene: SW Seawall
Mickey Crichton, Chief Climatologist for the New Confederate States Department of Coastal Defense, gazes towards the inbound noon ferry arriving from the port city of Lakeland, fifty miles to the southwest. Although this is not an official visit, Disney has given Mickey permission to examine the feverish efforts to strengthen the eastern and southern portions of the seawall.
Hurricane Johnnie, a devastating Category 5, is projected to arrive in the next four to five days. Although few people seriously expect it to breach the 120 foot high seawall surrounding this privately owned island city, it could seriously tax the pumping system that keeps the tourist mecca dry.
Since purchasing it from the NCS government right after the revolution, Disney has spent trillions on its defense system against the rising ocean, but now this icon of the Empire seemed vulnerable to the forces of nature. A few minutes ago Mickey had shuddered when the Secretary told him the news on the encrypted channel. Tomorrow the Confederate Weather Service shall announce the first ever revision of the Saffir-Simpson Scale. Category 5, formerly defined as greater than 155 mph will now be defined as 155-184 mph. Incredibly, Hurricane Johnnie hovers between the new Category 6, 185-214 mph, and Category 7, greater than 215 mph. Mickey must tell the Disney people before the CWT announcement.
The inbound noon ferry was still unloading as the outbound ferry approached the island dotted horizon on its way to Lakeland and the cruise ships there. Until now the Disney Empire had flourished despite all the threats imposed by global warming. Michael Eisner, CEO of the fledgling empire in the early twenty first century, believed in GW and prepared the company to take advantage of the coming events. Historians say that he even revised the secret by-laws set up by company founders Walt and Roy Disney; Roy, being a close friend of Mickey’s infamous ancestor Michael Crichton, fiercely opposed the changes but Eisner eventually won that battle before he retired in 2006.
As a seasoned and talented climatologist Mickey was already worried about Johnnie, even before the Secretary called. The trends had been looking ominous for years but the official change of the Saffir-Simpson Scale signaled a new era in the fight against
The preceding excerpt from the prescient short story by John M. Crichton III, written in 2035 by the young great nephew of the famous twentieth century novelist, finally galvanized the public and with it, the Federal Government, into action. Sadly, it was too late. Although scientists and foreign governments had been urging the US to cut back CO2 emissions for decades, the legacy of the second Bush administration and the influence wielded by his great uncle had been too strong. The public had been in denial and the massive disinformation campaign by the fossil fuel industries had stymied any legislative effort to enforce cutbacks.
Now, although the draconian laws passed in 2037 have cut CO2 emissions in half, the US is in a state of near collapse. Federal money diverted to the emissions effort has wiped out Social Security. Most other unneeded programs such as environmental, transportation, education, housing etc. have been cut to the bone. The Defense budget has tripled due to threats of invasion by the EU and the Asian Alliance.
Sea levels continue to rise at a rate never envisioned by climatologists and other scientists in the late twentieth and early twenty first centuries due to the unforeseen effects of
Figure 1 starts in 1850. Since many tropical cyclones/hurricanes don’t make land fall, and are of short duration, isn’t there likely to be under-counting in the first part of the graph? The data must be from ship-based measurements, so is double-counting possible early-on? No Category 5 was observed until 1920 or so; with poorer observations, could the maximum intensity of cyclones have been missed (seems like it)? I don’t know the definitions of the categories, but maybe it’s splitting hairs for the early data to be separated so finely.
Thanks,
Tim M.
[Response:There is a chance of undercount in the early part of the record, and I believe that nature would think the division of categories is fairly arbritrary as the windspeeds do not necessarily cluster at certain levels (as far as I know anyway…). Perhaps windspeeds and pressure (Fig. 2) is a better thing to look at? -rasmus]
I have the impression that one need to look at a much longer time scale than the last 1.5 century.
From history we know that the most devastating storm floods in the North sea region were in colder climatic periods, like the LIA. See the chapter on “Frequency of storms” in Europe at http://www2.sunysuffolk.edu/mandias/lia/little_ice_age.html
Even the last devastating flood in The Netherlands (1953) was during a slightly colder period.
Something similar can be seen in Antarctic ice cores: far more dust is settled in the ice cores during ice ages than during interglacials. This may be partly by dryer air and changes in vegetation, but also by more severe winds/storms during ice ages. See e.g. http://www.climate.unibe.ch/~hutterli/papers/Roethlisberger2002grl_c.pdf
Thus higher temperatures probably will reduce the frequency and severety of wind/storms, not increase them. Or it may be that it is the temperature difference between regions (or even equator and poles), that drives wind speed/storminess? The temperature gradient between equator and poles is higher during ice ages than during interglacials…
[Response:I think that this may depend a bit on the type of storms that you are referring to. Mid-latitude storms are most active during winter, i.e. cold season, when the Arctic experiences polar nights and there is stron temperature gradients. Your comments may well be true for these. Hurricanes, on the other hand, are most active in the summer season and when sea surface temperatures are high. -rasmus
Re: Comment by Ferdinand Engelbeen â?? 5 May 2005 @ 8:46 am
I think you make an excellent point, Ferdinand.
One theory is that the LIA was caused by changes in roiling patterns by the moon. See: http://www.pnas.org/cgi/content/full/070047197 I agree with this theory and take it one step farther, that the gravity pattern changes are about roiling and outgassing of CO2, which then changes conductivity patterns. The problem is that when you introduce CO2 as your varied input to this dynamic, it is dependant to both LIA and LCO–and it is my view that’s why we are seeing an AMPLIFICATION. With all things electrical, the problem with amplification is INSTABILITY. What appears to be going up twice as fast twice as quickly will come down the same way.
Re: Max hurricane speed/wind pressure data
Do you need an account to access the raw data at the NOAA site?
Thanks
[Response:No. It took some searching to find. If you click on the link to the R-script, you can get the URL (you can also get R from ‘http://cran.r-project.org’ – runs on Windows, Linux and Mac – run the script, and it will retrieve the data for you… ]
GAVIN: THANK YOU FOR THE SITE.
THERE APPEARS A WEALTH OF HARD DATA IN NAVEL ARCHIVES OF NUCLEAR
SUBMARINES THAT OPERATE AT GREAT DEPTHS AND MAINTAIN LOGS ON OUTSIDE
TEMPERTURES AND SALINITY. ALL COUNTRIES WHO OPERATED THEM,
WITHOUT A COMPLEX MODEL, COULD PROVIDE TIME, LOCATION, DEPTH, OUTSIDE
TEMPERTURE AND SALINITY. DATA COULD BE SOLICITED WITH NATIONAL ANANIMITY
AND COMPROMISING LITTLE.
WE COULD GLIMPSE INTO THE DYNAMICS THAT MOVE VAST QUANTITIES OF HEAT.
I’ve been using hurricanes as a good measure of the maximum energy available in the atmosphere (ie if more energy is present then you get more & bigger hurricanes). I differ by counting the width of the hurricane, the amount of rain, and the average windspeed as the relevant measures of relative energy.
Why is hurricane windspeed such an important consideration when it is more based on ideal conditions such as symetry?
On the frequency of the storms, I note that the weather really didn’t change much during Dec 04 and part of Jan 05 such that you had four distinct spots in the oceans at 90 intervals in the Southern hemisphere that showed substantial chilling compared to historical data. This fits well with an increased circulation model where there is a competition of space for storms to form so they end up as static waves. To get an exceptional number of storms you only have to be on the right side of a high pressure zone that herds the storms into a narrow path. Voila you have Florida being hit with 4 hurricanes in 2004 because there was a high pressure off the East coast of the US that didn’t vary much or break down.
This supports counting increased storms as an indication of climate change. Would it not be better to track the high and low pressure systems that guide these storms?
Could you point to ‘standard’ climate physics texts? I am a mathematician by training and I would like to learn about the technical aspects of the subject. Or perhaps some review papers (maybe even available on-line).
I love the site and appreciate the fact that answers are by people actively working in the field. Keep up the valuable work.
Thanks,
Michael
[Response:Depends a bit on whether you mean basic atmospheric physics, or of-climate-change. The Climate System from the IPCC report, and the rest of the report, might help a bit. Large-Scale Dynamics of the Atmosphere has some good pointers (esp James, circ atmos, which is suitable for mathematicians) – William]
[Response: One good reference is: Robert Pearce’s (2005) “Why must hurricanes have eyes?” in Royal Meteorological Society’s journal Weather, vol 60, No. 1, p. 19-24. -rasmus]
I actually find this post and discussion of it bizarre. Has anyone bothered to read the re-analysis project and not just go in and grab a bunch of numbers and plug them in and then start speculating? It is clearly pointed out that the intensity is underrepresented in the data prior to air and satellite reconnaissance. This was demonstrated in figures 3 & 4 of for hurricane Erin of the Re-analysis project. It is also clearly pointed out that the record is by no means complete for frequency or intensity. Landsea was the principal investigator, I am curious as to why he was not asked for input about accuracy. In addition, I might point out that the re-analysis is not complete. A complete re-analysis for 1911-1943 remains to be done as well as a re-analysis of intensity since 1944.
As a Biologist by training, much of the specific nuances of climate discussion gets out of my league pretty quickly. However, some pretty obvious questions about this reporting came to mind pretty quickly and were easily confirmed. I doubt as a scientist I would try to use admitted woefully inadequate old historical data and combine it with very sensitive modern data and make leading statements about “emerging signs” of change and that it should be a part of normal scientific discourse. Personally, I am all for scientific discourse, but not one that uses very subjective data (as clearly pointed out in the re-analysis of data at the NOAA Hurricane Research Center) as strength of the argument.
One question I ask. Do you not find it curious that in figure 2 (Maximum Hurricane speed/Min pressure graph)of this Rasmus post, that the shift to lower pressures was abrupt starting in the late ’60s early 70’s? This makes me wonder if what we are seeing is an artifact of how pressures were either measured or calculated. Perhaps a re-analysis of the data since 1944 will clear this question up.
To conclude – I will add that the investigators of the re-analysis project had the following conclusion for Cycles of hurricane activity: These records reflect the existence of cycles of hurricane activity, rather than trends toward more frequent or stronger hurricanes.
http://www.aoml.noaa.gov/hrd/hurdat/Documentation.html
[Response:You are right that the data probably may not be 100% representative, due to improved the fact that the observational capabilities have improved over time and the fact that most storms nowadays are detected whereas some may have gone undetected in the past. It’s not just the observational systems, but also the fact that we often can identicfy in weather forecasts (model simulations) conditions that are favourale for such storms, so that we know in advance when too keep a watchful eye. But, as far as I know, this data is the best information that we have about past hurricanes/storms. Even if it’s not 100% perfect, it’s still interesting to analyse – it would my opinion it would be silly not to. I am aware about possible limitations of these data, and therefore included the link at the bottom, but these are still the best informaton that we have. Furthermore, there have been independent measurements/analysis of dew-point temperature from radiosondes in the Tropics. But, I don’t understand why you call this discussion ‘bizzare’. I can agree that the ‘Disney’-comment can be characterised as bizzare, but do you really mean that a discussion of data is bizarre if the data may contain errors? -rasmus]
Rasmus,
How was peak-windspeed measured/assessed with the early manual ‘run of wind’ type cup anemometers?
Were they on open-topped 10m lattice towers and how often would one find an observer standing on the top of these during 300mph storms?
I appreciate that UKMO electric (remote) anemometers probably lagged being US ones, but in 1939 the UK type was a ‘run of wind’ pattern that ran an bell after a given number of turns.
The Generator-type anemometers only became UK std during WW2:Looking at the post-1945 data of your plot there is no upward trend in windspeed, indeed it declines slightly.
[Response:You’re of course right if you are a bit critical about the wind speeds and central pressures. You would risk being blown away if you tried to measure the maximum wind speed of a hurricane or the pressure drop in a hurricanes eye. I did not make such measurements and presume that they have been inferred from other storm characteristics. In the modern time, Doppler shift measured by radar can nevertheless give more accurate estimates. Therefore I emphasised that the analysis presented here took the data at face value – this is the best information we presently have at hand. -rasmus]
Let me pass on some information which i have come across in the past few weeks. This information was sent to me from NHC to which i wish to thank for there response to my questions.
There as been a “above normal” levels of activity since 1995 (average seasonal activity in the atlantic basin is 9.8 named storms of which 5.8 became hurricanes). Just for comparison, in 2004 there was 15 named storms 9 of which became hurricanes and 6 of the 9 hurricanes were “major” with winds of 100+ mph.
the years 1995-2000 experianced the highest level of north atlantic hurricane activity on reliable record. Compared with the general low activity of the previous 24 years (1971-1994), the past 6 years have seen a doubling of overall acidity for the whole basin, a 2.5-fold increase in major hurricanes (>50 meters per second), and a 5-fold increase in hurricanes affecting the caribbean. The greater activity results from simultaneous increase in north atlantic sea surface temperatures and decreases in vertical wind shear. Because these changes exhibit a multi-decadel time scale, the present high level of hurricane activity is likely to persist for an additional 10 to 40 years.
I would also like to add that the seasonal outlook for 2005 should be due mid may. This is issued by NOAA. Once again i would like to thank all the people who keep us all informed on issues of great importance.
Comment #19 says :
Compared with the general low activity of the previous 24 years (1971-1994), the past 6 years have seen a doubling of overall acidity for the whole basin…
What would be the conclusions you would draw from the activity over the 25 years (1945-1970) compared to the past 6 years (and why choose 6yrs)
Do you allow for a greater variation in a 6 yr period than a 25yr period ?.
rasmus,
I do indeed find the post and subsequent discussion bizarre. You use words such as “may” and “might not be 100%” in your posts when words such as “likely contains errors” is more accurate. This is underselling the limitations of the data. Both Neumann et al. (1993) and Landsea (1993) recommend only utilizing data since 1944 for computing climatological statistics. I remind everyone that Landsea is one of the principals on the re-analysis project. From the Re-Analysis document I recommend that you review the sections The Work of Jose Fernandez-Partagas and Center Fix Files. Often the number sets on Hurricanes given are calculations made from deductions of eyewitness accounts. In other words, (educated) guessed at. When equipment readings did become available, there were calibration problems or sustained winds destroyed the equipment at a certain intensity.
I recommend reading the following as a minimum from the Hurricane Center before even beginning discussions of the data.
http://www.aoml.noaa.gov/hrd/tcfaq/E11.html
http://www.aoml.noaa.gov/hrd/tcfaq/G4.html
http://www.aoml.noaa.gov/hrd/tcfaq/G3.html
Your response to me in my post (#16), is also puzzling. I question whether we are surpassing the limit of what historical data can answer with respect to in intensity and strength. Statement of this is based my own interpretation and interpretation of the investigators. You then seem to imply that I demand “100%” in the accuracy of the data before it should be looked at and that if we can’t get “100%” it should be discarded. Of course that would be silly. I am also a Scientist and understand that there is not going to be 100%. The point being made is, that one has to understand the limitiations of a set of historical data before it is used to make speculation. I did not review the Gettleman et.al (2002) evaluation of dewpoints in the Tropics. It seemed a very minor point in your post when I read it. If you think it so important I will read it if I have time.
So is the historical hurricane data useful? Absolutely. This is what is being used to deduce the cyclical nature of hurricane activity over the past hundreds of years. It is also being used to show storm tracks back into the 1800’s. I think it would be interesting to know if there are patterns of changes in hurricane paths through history.
I also would direct everyone to a primer by Chris Landsea on Hurricanes and Global warming posted on the Prometheus Science Policy Blog web site for perspective.
http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/000322landsea_on_hurricane.html
One final point while writing. It is about post # 18 (I am not attributing this to you). This caught my eye because it sounded familiar. This post appears to be downright dishonest in the selective editing of information. Again I recommend everyone read the Hurricane centers FAQ’s I linked to and the Landsea primer to see what the post edited out. Of particular note, among other things, is dropping any mention that the present high level of hurricane activity is thought to be “cyclic” through history.
To conclude, I do find the original post bizarre because it just never occurred to me that someone would use the data in this manner if they had read the whole re-analysis document.
[Response:Thanks for clearing up the issue! I appreciate you comments. -rasmus]
Once again, the vitriol from those who are convinced there is a great conspiracy to promote the global warming story comes through loud and clear. I think the current situation could be stated quite calmly as: there are two clear possibilities: (a) the data is not good enough to draw a conclusion, or (b) the data might be good enough to draw a conclusion. I thought the opening article made that fairly clear. Furthermore, what Stickery describes as selective / dishonest editing is no such thing. It is extracting a few facts from an article without reprinting the entire article or listing every conceivable qualification or mentioning the hometowns of the authors – which I think is still considered okay in most sciences. Maybe not though.
Now, putting my critic’s hat on, and not wishing to align myself with the vitriolic skeptics, I do think there is an issue with the accuracy of the data that has not been discussed: has any data analysis accounted for changes in frequency of observation?
As wind-speed and barometric pressure are highly variable from hour to hour in a hurricane, it stands to reason that the more frequently you take measurements, the more higher the “maximum” windspeed and lower the “minimum pressure” are likely to be. And I believe, as a semi-educated lay-person, that these measurements are often on an every-three-hour schedule now, whereas in the past they were generally less frequent. Maybe I am wrong on this. But if it is the case, I would hope the data would be corrected for this statistically before making a time-series comparison.
– Dan
rasmus,
comment #19
Perhaps if you could see the document that was sent to me by e-mail you your self could draw your own conclusions. I was only sharing information that had been sent to myself. I leave this up to yourself and hope to hear from you. I am just one person that takes an interest in what is happening to our planet and sometimes find it hard to understand the jargon in which information is sometimes relaid to the public.
Beginning in 1995 there has been an increase in the frequency and intensity of hurricanes in the Atlantic basin. However, this increase is very likely a manifestation of a natural multi-decadal cycle of Atlantic hurricane activity that has been occurring for the last few hundred years. For example, relatively few Atlantic hurricanes were observed in the 70s, 80s and early 90s, but there was considerable activity during the 40s, 50 and early 60s. Also, the period from 1944 to 1950 was particularly infamous for Florida – with 11 hurricanes hitting the state during those years. (this last paragraph is from Landsea posted on the Prometheus link provided earlier)
I hope most everyone would agree, taking just the first sentence of the above paragraph without at least mentioning some of the content of the rest of the paragraph would misrepresent the author’s intent. I hope this is not considered okay in most sciences. I suggested that post # 18 may have gone to this point of editing because much of what I have gotten from the Hurricane center (or many other a place on the internet that cites Landsea) usually has some version of the paragraph. If this was not a case of selective editing as I mentioned it appeared to be and is as the poster received it, I do offer an apology to Gary.
Another few points to clear up – I did not accuse Rasmus of dishonest editing. I specifically stated I wasn’t. He did as Dan Allan (#21) indicates – he extracted the data without reprinting the whole article. I challenged some of the use because Rasmus was using data in a manner that was pretty much recommended against. If this is to be done, I do feel it appropriate to provide a rational for doing so. This was not done so I challenged it. This is not an extreme point, it is a very basic one. I have not asked for every conceivable qualification nor do I care about hometowns of authors.
Dan Allan is correct in stating the data set for figure 2 can be distilled down to a) it is not good enough to draw conclusion b) it is good enough. I have challenged the use of the figure and provided the links and information to support my position as to why the data is not good enough to draw a conclusion with respect to wind speeds (comments #16 and #20). I added that our current prevalence of hurricanes is thought to be a part of a natural historical cycle of Atlantic hurricane activity. This is a prevailing theory, was not brought up in the post and is supported by the historical record. I specifically tried to stay away from providing links that descend into the politics of hurricanes and climate change..
To conclude – I do think some questions from the historical data that might be answered that I have alluded to. Perhaps Rasmus or someone else knows the answers-
a)storms paths in the historical record – are there any significant changes over time that are not part a natural cycle?
b)Are there any detectable trends in Figure 2 if just data since 1944 is used?
And finally at the risk of opening another can of worms –
— has anyone looked at changes in the number and pattern of storms in the South Saharan desert. If so, how large of a factor will this be in the number of hurricanes and their track?
And an admission for Rasmus – OK the post – Disney Fall of the Empire is the bizarre post….so much so, it is downright funny. I may be wrong, but the extremes of all sides of the global warming issue may be being mocked.. ;)
One additional comment regarding post #7. This post challenges the inclusion of data relating to tropical storms in a graph and discussion relating to hurricanes, and wonders if this is a case of “padding the data”.
Yet, if tropical storm data were excluded, wouldn’t the accusation then be that the author is, “selectively editing the data”?
It seems that, with some critics, there is simply no winning. Of course, since hurricanes and tropical storms are all just degrees of intensity of the same type of storm – tropical cyclones – and since there are a very limited number of data points of one limits the data to hurricanes, it makes sense to include tropical storms.
NOAA predicts another higher than normal hurricane season for 2005 and indicates that many years in the future will see higher than normal hurricane frequencies and intensities:
http://www.noaanews.noaa.gov/stories2005/s2438.htm
Perhaps the increasing SSTs due to climate change is the most likely cause of this increasing frequencies and intensities.
From the NOAA 2005 hurricane season prediction:
“Also expected this season is a continuation of tropical Atlantic SSTs that are warmer than can be accounted for by the multi-decadal signal. This additional warmth is more conducive to hurricane formation than would be expected from the multi-decadal signal alone.”
I diligently searched the site but could find no information or even speculation as to what the cause of that additional warmth might be. This is perhaps no surprise given Landsea’s recent outburst. One might also speculate that NOAA, which like many federal science agencies has become more politicized under the Bush regime, is loath to mention any potential anthropogenic connection given the undesirable (to the Bushies) political consequences that might then result from a bad hurricane season.
Rasmus, do you know of any fresh information on the causes of the SST increase from other sources? Also, how does SST relate to the dew-point temperature in the Gettleman paper (which I don’t seem to be able to access)?
Note also this interesting graphic, which shows SST being tracked globally on a weekly basis: http://www.emc.ncep.noaa.gov/research/cmb/sst_analysis/images/wkanomv2.gif.
Things are clearly warmer in the tropical north Atlantic, but what is the global net? From this and other graphics on the site (back the URL up to “/sst_analysis” to see everything) it looks like there may be an overall warming (basing this on there being more extensive areas of high-temp yellow than low-temp green), but I couldn’t find any calculation showing the net, either currently or over a period of time.
Finally, setting aside the hurricane issue, how important is the SST trend (if any) to the models?