Is the Atlantic hurricane season getting longer?
It seems like there have been an unusual number of early and late season tropical storms and hurricanes in the Atlantic in recent years. In 2008, we had four named storms in July, and the second most powerful November hurricane on record. Both 2007 and 2005 had rare December storms, and 2003 featured Tropical Storm Anna, the first April tropical storm ever recorded. This year, Hurricane Tomas made 2010 the fourth straight year with a November hurricane, something that has never occurred in the Atlantic since accurate records began in 1851. Is hurricane season getting longer? Dr. Jim Kossin of the University of Wisconsin published a 2008 paper in Geophysical Research Letters, "Is the North Atlantic hurricane season getting longer?" He concluded that yes, there is a "apparent tendency toward more common early- and late-season storms that correlates with warming Sea Surface Temperature but the uncertainty in these relationships is high".
Figure 1. Observed sea surface temperature (SST) trends during the official North Atlantic hurricane season (June-November) for the period 1950-2007. Units are °C per century. The dashed rectangle denotes the tropical storm formation region south of 30° North latitude and east of 75° West longitude. Data are from the NOAA Extended Reconstructed Sea Surface Temperature V3 product [Smith et al., 2008]. Image credit: Kossin, J., 2008, "Is the North Atlantic hurricane season getting longer?", Geophysical Research Letters, Vol. 35, L23705, doi:10.1029/2008GL036012, 2008.
Methods
Dr. Kossin utilized the "best track" database of Atlantic tropical cyclone activity going back to 1851. However, since lack of satellite and aircraft reconnaissance data before 1950 makes the early part of this record suspect, he limited his analysis to the period from 1950 onward. The era of best data--the satellite era beginning in 1980--was also looked at separately, to ensure the highest possible data quality. The area studied was only a portion of the Atlantic--the tropical storm formation region south of 30° North latitude and east of 75° West longitude. This region has shown considerable warming of the Sea Surface Temperatures (SSTs) since 1950, in excess of 1°F (0.6°C) (Figure 1). A statistical method called "quantile regression" was employed. The method looked at how certain thresholds that mark the beginning and end of hurricane season have changed over the years. For example, the date where 5% of all tropical storms form earlier than that date, was called the 0.05 quantile, and the date where 5% of all tropical storms form later than that date, was called the 0.95 quantile. Kossin was able to show that the date of the 0.05 quantile got steadily earlier and the date of the 0.95 quantile steadily got later since 1950. Hurricane season for both the period 1950-present and 1980-present got longer by 5 to 10 days per decade.
Figure 2. Trends in tropical storm formation dates, in the region south of 30° North latitude and east of 75° West longitude, at the 0.05.0.95 quantiles. Trends are based on the periods (left) 1950-2007, and (right) 1980-2007. The dates (month/year) associated with the 0.05, 0.25, 0.50, 0.75, and 0.95 quantiles for each period are shown on the top axis (these threshold dates are based on the full sample for each period). Shading denotes the 90% confidence interval. Image credit: Kossin, J., 2008, "Is the North Atlantic hurricane season getting longer?", Geophysical Research Letters, Vol. 35, L23705, doi:10.1029/2008GL036012, 2008.
Relationship with Sea Surface Temperature
The broadening of the Atlantic hurricane season found was strongly dependent upon Sea Surface Temperatures. Both the onset and end of hurricane season shifted by 20 days per degree C of warming of the SST. With global warming projected to increase tropical Atlantic SSTs 1-2°C by the end of the century, can we then expect a 40-80 day increase in the length of hurricane season? Dr. Kossin doesn't explore this possibility, and doesn't blame the observed increase in the length of the season on human-caused global warming of the oceans. There is reason to believe that future warming of the Atlantic SSTs won't necessarily broaden the area over which tropical storms will form, though. Papers by Henderson-Sellers et al. (1998) and Knutson et al. (2008) theorize that as SSTs warm, the lowest temperature at which tropical storms can form will also increase. The current minimum temperature of 26.5°C (80°F) may increase to 28.5°C for a 2°C warming of Atlantic SSTs. Johnson and Xie (2010) have found observational evidence that the lowest temperature at which tropical storms can form has indeed been increasing at about 0.1°C per decade in the Atlantic, in line with climate model predictions.
References
Henderson-Sellers, A., et al., 1998, "Tropical Cyclones and Global Climate Change: A Post-IPCC Assessment", Bull. Am. Meteorol. Soc. 79, 19–38.
Johnson, N.C., and S.P. Xie, 2010, "Changes in the sea surface temperature threshold for tropical convection", Nature Geoscience doi:10.1038/ngeo1008
Knutson, T.R., J.J. Sirutis, S.T. Garner, G.A. Vecchi, and I.M. Held, 2008, Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions", Nature Geoscience 1, 359 - 364 (2008), doi:10.1038/ngeo202
Kossin, J., 2008, "Is the North Atlantic hurricane season getting longer?", Geophysical Research Letters, Vol. 35, L23705, doi:10.1029/2008GL036012, 2008.
Jeff Masters
Reader Comments
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Nothing glib there, I was sincere.
To say that the population of the earth is self correcting is profoundly askew to a realistic, stewardly philosophy amigo.
Of course the US growth continues up as more people immigrate. To look at the issue responsibly, you should look at the standard growth metric called the "birth rate".
Take your pick of pages showing maps of the world and where babies are coming from:
http://p2o2.blogspot.com/2008/07/bye-bye-cosy-europe.html
You'll find that overpopulation is a problem coming from poor economic conditions. The problem is *not* overpopulation, but rather awful economies. Solutions should address the root problem, economics.
I didn't realize you were my amigo.
Realistic philosophies are based on the facts at hand. Realistic philosophies do not come from a misplaced notion that the world is overpopulated.
Almost all of Europe has a declining birth rate. Not self correcting? It's not from population restricting measures, mi amigo, it's from a self correcting measure that happens when countries establish a nice standard of living and no longer need large families to maintain that lifestyle.
Solutions aren't found by yelling on the street corners about the end of the world. It's about realistic philosophies that strive to boost the economies of developing nations without using misplaced ideas such as population limits. That only acts *against* the establishment of strong economies, ironically. You're part of the problem, not the solution.
Sorry that tonal inflections don't come across on keyboards. If you feel I have insulted you, then I appologize, Sir.
But, I think Sophism may exist in the Science of Economics as well. If you sincerly beleive that overpopulation in third world countries is due to need and if you sincerly beleive that overpopulation in certain races is due to need, then we'll just have to disagree.
Actually, I do.
Sometimes I grit my teeth, but yes I do. LOL
As it stands now, GW cannot be stopped. We can try to reduce its impact, but not stop it entirely. Although it has been warmer than it is predicted to be, it's about the rate of warming, not just how much it warms by. When a six-degree warming occured in the Permian-Triassic, 90% of all life went extinct. This amount of warming is possible within the next 100 years. The extra fast warming is releasing feedback mechanisms, which is making it accelerate even faster. We've been in a stable climate for the past 10,000 years, and that's all about to change. Although climatic stability is rate in Earth's pre-Holocene period, the sudden reversal of the current stability, as a fellow Wikipedian puts it, "will be seen as nothing short of apocalyptic".
He was in post 108 or something like that. I have one person on my poof list: 15hurricanes.
The reason why the minimal threshold for storm formation might increase from 26.5°C to 28.5°C is as follows:
Warming Ocean -> More Deep Convection & Latent Heat Release Aloft -> Warming of the Upper Atmosphere
Currently 26.5°C and higher SSTs generally lead to unstable conditions that foster deep convection. However, if the upper atmosphere warms the ocean would have to warm as well to maintain instability.
It all has to do with environment lapse rates...
1. The Data Record is too short
2. Pre 1980's storms may have been missed - not sure if they would preferentially be missed at the beginning/end of the season because storms then are likely to be weaker/have shorter duration
3. Warm phase of the AMO switched in the middle of the satellite period - so the increase in season length after 1995 could largely be due to warmer SSTs
4. Shear/Dry air are typically the major limiting factors during the early/late parts of the season in the Atlantic Basin - though higher SSTs do play a role
Or.... weather pattern shifts cause GW. ;)
While I respect your stance, I do think that once countries become developed, the birth rate goes down, sometimes below the death rate. For instance:
Birth Rate (per 1000)- Death Rate (per 1000)= new people (per 1000)
Italy= 8.36-10.61= -2.25 new people (per 1000)
Canada= 10.29-7.61= 2.68
United States= 14.18-8.27= 5.91
Japan= 7.87-9.26= -1.29
Australia= 12.55-6.68= 5.87
New Zealand= 14.09-7.00= 7.09
Denmark= 10.71-10.25= 0.46
Estonia= 10.28-13.35= -3.07
Finland= 10.39-10.00= 0.39
Iceland= 13.50-6.81= 6.69
Ireland= 14.33-7.77= 6.56
Latvia= 9.62-13.63= -4.01
Lithuania= 9.00-11.12= -3.12
Norway= 11.12-9.33= 1.79
Sweden= 10.15-10.24= -0.09
United Kingdom= 10.65-10.05= 0.60
Austria= 8.66-9.91= -1.25
Belgium= 10.22-10.38= -0.16
France= 12.73-8.48= 4.25
Germany= 8.18-10.80= -2.68
Liechtenstein= 9.86-7.42= 2.44
Luxembourg= 11.77-8.43= 3.34
Monaco= 9.09-12.06= -2.97
Netherlands= 10.53-8.71= 1.82
Switzerland= 9.62-8.54= 1.08
Cyprus= 12.56-7.76= 3.80
Russia= 11.03-16.06= -5.03
Hong Kong= 7.37-6.6= 0.77
Malta= 10.33-8.29= 2.04
Singapore= 8.99-4.53= 4.46
Spain= 9.87-9.90= -0.03
Portugal= 10.45-10.62= -0.17
Greece= 9.54-10.42= -0.88
Slovenia= 8.99-10.51= -1.52
South Korea= 9.09-5.73= 3.36
Taiwan= 8.99-6.65= 2.34
Czech Republic= 8.89-10.69= -1.80
These are all the countries that are considered "developed." Notice that most of them are under 7.00, and there are only a handful over 5.00. As you can see, the United States is not done with its process and that number is likely to go down. To show you how low these numbers are, here's Sierra Leone for comparison:
45.08-22.26= 22.82 new people (per 1000)
If all the undeveloped countries could be raised to developing or developed standards, world overpopulation would not be a problem.
Okay thank you I was trying to figure that out.
World overpopulation is very much a short-term problem, and one that is mostly restricted to developing countries. In fact, in some developed countries, we may even see "not enough people" become a problem. Although a global population of around 12 billion by 2100 will further exuberate our economic and environmental crises, we have much bigger problems ahead of us.
Got ur back on this one. NW passage prolly was last open when Greenland was green enough to earn the name, say, maybe 600 years ago? 1000 years ago? Anyway, my point is we are missing a lot of the data we need to confirm some of the hypotheses out there.
That being said, just because data wasn't collected the way is is being collected now, we can't assume that the data is completely invalid. For example, the fact that we have better coverage of the EATL via satellite today doesn't mean that there was no ship's data available from the area 100 years ago.
We all benefit more from directing our attention to using our data wisely and allowing both enthusiasm and skepticism to be healthy rather than rabid. If more of the so-called scientific reporters and commenters on both sides of this issue would be more objective in their word choice, we might actually get a better understanding of the real science. Nobody benefits from the you-say-I-say.
I think some people on both sides of the issue can benefit from eliminating the judgemental name-calling.
I also think links to sources for this topic should be clearly focused.
I don't think we can avoid discussion of this topic, since it impinges so directly on the purpose of this blog (and this website!), but it behooves us to make the conversation worth the while, doesn't it?
Completely agree. We didn't necessarily miss whole storms when we had 2 ship obs and those ship obs may be good data. Some of the classifications, such as number of TSs and/or when they happened has some serious questions, though.
Remember earlier this year when we are all calling a system a TS and due to lack of QuikScat data showing a closed system, NHC was slow to call it a TD? Comparing the historical (> than 20 years ago) to now is very much like comparing the proverbial apples to oranges.
"just because data wasn't collected the way is being collected now, we can't assume that the data is completely invalid" This is so true of surface stations. The historical surface ob data as a representative value for an area and/or a component of a mean global telephone number is likely far more valid than the same for today.
Thanks for the civility comment...hope it gets through to everyone.
Complete Blog Refresh
Mirror Site
Can't we be good husbands of the "vineyard" of the earth? If we destroy our home, we don't have a guarantee of being granted another one.
Hey, I even read the FOX News one, and I have found FOX to be remarkably biased towards whatever their current bias of the week is in their reporting . . . .
It's called rebuttal, not disrespect.
He makes a good point too, since some of the areas where populations have been on the rise are also areas with potential water shortages.
I'm in ''lurking'' mode...I also find find STL's post to be quite informative and accurate.
I may disagree with him, but when I do, I can prove my point with more data... just because you don't agree with someone doesn't mean their argument is invalid.
The density is largely the issue; another is reproduction rates... Singapore is in no way, shape, or form poor. (no offense) But I get your point.
The reliance on outside sources is a different topic, but the relationship between density and arable land is related to overpopulation.
What I like best about the blog is when we can slam each other with the data LOL. I get a real education out of it.
I guess that's why I was annoyed with the two reports about GW I saw this past week, where each reporter sounded more like one of our local summer bloggers in defense of his / her position than like well-trained, scientific journalists. Just about the only thing missing from one of them was the "but he started it first". . . lol. What's the world coming to the the bloggers are the sound voice of reason and the reporters are "he-saying and she-saying"???
Yeah I do too...dont really think that there annoying. Sometimes the stuff he posts is interesting.
My bigger concern about the GW issue is not what the cause is so much as what the impacts are likely to be. I agree we should consider causes; if we can mitigate against the effects by shutting down the cycle I can see the value of that. OTOH, it seems that anything we do now will still leave us with quite a few years when we will have to cope with a least some of the consequences. That's why I found the comments about overpopulation, developed vs. developing, and land / water use so interesting. If arid areas are going to spread or shift in scope, for example, what are the potential impacts on food production in that part of the world?
Somebody mentioned earlier the role of TCs in moving water into the SE US, and I know they perform similar functions along the SE African coast (and prolly to a lesser extent to NW Australia). How might shifting temperatures affect traditional storm tracks, storm rates, etc? We've seen a short-term shift on the basis of La Nina / El Nino vacillations, so we know something similar, but longer lasting isn't out of the range of possibility.
I'm also thinking about the Grey/Kolbach Dec forecast, which the good doc repeatedly reminds us has little skill. Nevertheless, it does indicate that hurricane predictors can / do shift based on climate-based patterns, so that things we used to read before as indicators may no longer be so reliable.
Just a few thoughts.
Tropical Cyclone Warning Number NINE
TEMPETE TROPICAL MODEREE CINDA 04-20082009
04:00 AM Reunion December 18 2008
======================================
At 0:00 AM UTC, Moderate Tropical Storm Cinda (994 hPa) located at 11.3S 66.9E has 10 minute sustained winds of 35 knots with gust of 50 knots. The storm is reported as moving south at 4 knots.
Gale Force Winds
===================
20 NM radius from the center
Near Gale-Force Winds
====================
30 NM radius from the center extending up to 70 NM in southern semi-circle
Dvorak Intensity: T3.0
Forecast and Intensity
=========================
12 HRS: 12.0S 66.6E - 40 knots (Temp%uFFFD Tropicale Modere%uFFFD
24 HRS: 13.4S 65.7E - 35 knots (Temp%uFFFD Tropicale Modere%uFFFD
Additional Information
======================
System has reached moderate tropical storm stage during the night and given the name "Cinda" by Mauritius Meteorological Services at 0000z. Stronger winds extend further in the souther semi-circle, due to the gradient effect with the subtropical high pressures. The potential for intensification of this system appears limited. Environmental conditions are still expected to deteriorate starting today.
Good evening, all! Yup, Simon. I've done some reading in the past about "sustainability." I'm curious, according to the graph (as I see it) why do you think it's supposed to take about 20 years to go from eight to nine billion - especially, since it's only supposed to take about 10 years to go from seven to eight billion? Seems with that many more people having babies that it would take nearly as much as 20 years to grow exponentially again.
o welcome home
they're getting farther apart...
Cindy or Cinda??
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