Are Hurricanes Really Becoming More Intense?

[donsutherland1]

There was a recent study that suggested that hurricanes are becoming more intense, on average, than in the past. That study cited the higher frequency of Category 4 or stronger hurricanes since 1990 relative to the 1970s to reach its conclusion.

The September 15, 2005 issue of USA Today reported, "While studies have not found an overall increase in tropical systems worldwide, the number of storms reaching categories 4 and 5 grew from about 11 per year in the 1970s to 18 per year since 1990, according to a report in Friday's issue of the journal Science.

In my view, that study is fatally flawed for two reasons:

1) The comparison to the 1970s is not valid, as it compares Atlantic activity during a long-term cool cycle against that during a long-term warm cycle.
2) Measurement techniques have advanced in recent years to the point where it is plausible that some Category 4 hurricanes in the past, especially during the last warm cycle, might not have been assessed correctly.

Warm cycles typically see a period of years--usually about a decade--in which there is a burst of major hurricane formation. Let's compare the 1945-55 "burst" with the 1995-2005 one.

Again, it should be noted that measurements were not as precise in the past as they are today and there were not satellites until the 1960s. Hence, it is plausible that a number of hurricanes that reached Category 4 or above status in the 1940s and 1950s might not have been assessed correctly while out at sea.

Category 4 and Above Hurricanes:
During the 1945-55 period, 19/115 (17%) of tropical cyclones reached at least Category 4 status in the 1945-55 period. In the 1995-2005 period (inclusive of Rita), 27/156 (17%) of tropical cyclones have reached Category 4 or 5 status. The 1995-2005 period has seen somewhat more frequent formation of such storms, but measurement issues might well explain at least some of the difference.

Major Hurricane Formation:
The broader measure of major hurricane formation (Category 3 or above) shows that such formation of major hurricanes was more impressive during the peak of the last warm cycle than at present. During the 1945-55 period, 42/115 (37%) tropical cyclones grew into major hurricanes. So far, 1995-2005 (through Rita) has seen 43/156 (28%) tropical cyclones grow into major hurricanes. Thus, the 1945-1955 period saw tropical cyclones grow into major hurricanes approximately 32% more often than the current period.

Conclusion:
The only issue I see right now is that it is not yet certain whether we are at the peak of the current warm cycle. Given that the TNA has reached record levels (July destroyed the old record; August narrowly beat 2004 and 1998), we're probably close to the peak or perhaps there. Time will tell.

In sum, I'm skeptical of the outcome of the aforementioned study. Given that it compared a warm Atlantic cycle with a cool one, not to mention measurement issues for earlier periods of time, I don't have much confidence in the validity of that study.

[sponger]

Don, those were my thoughts exactly when I saw the study. Unfortunately, the envirionmental movement has been hijacked by a group with a agenda who line up facts to support their goals. That is never good science.

The effect of this is more and more people are turned off at data that suggests we cause global warming because of past attempts to manipulate the data. Great post.

[LAwxrgal]

I'm inclined to agree, Don. I don't think the number of major "monster" hurricanes is more, I think technology is much better able to detect them. It seems like they're more frequent because of that.

[HURAKAN]

Don, really interesting. Furthermore, yesterday I did a little research about when was the last September that had seen 5 hurricanes like year, and the answer is September, 1955. Which correlates to your research of the impressive overall activity between '45 - '55.

[DESTRUCTION5]

I think We've always had Monster Canes..Thier just now of a sudden makign landfall int the US..

Look at the W Pacf....150 MPH Super Typhoons every day of the week..

[donsutherland1]

Sponger,

I don't disagree that some portion of warming that has been occurring has been caused by human activity (heat island effect, CO2, etc.). Natural causes are also contributing However, a lot of questions remain to be answered in terms of the allocation of warming.

Moreover, so far, it is very questionable whether the warming has actually had an impact on tropical activity. Dr. Gray argues that it hasn't, as one has not yet seen a statistically significant increase in worldwide tropical activity.

Of course, there are also questions as to whether global warming would generate greater tropical activity. In prehistoric times, there was a steady-state El Niño and global warming might well trigger a return of such a phenomenon. If so, then even if tropical cyclones are stronger, on average, they might not be more frequent. Again, this is just a possible scenario, but one that would need to be explored further to better understand the implications of global warming should it progress as some models forecast.

Having said that, the study in question likely does more to create confusion than actually address real issues. It is unfortunate that the study's authors went ahead to compare a cool cycle with a warm one. Given their credentials, I find it difficult to believe that they are not aware of such Atlantic cycles.

In the end, research on this issue and others, really needs to be based strictly on scientific merit and be sufficiently rigorous so as to have confidence in the conclusions. Politics should stay out of the research. Otherwise, findings could be tainted (perhaps in fact and perception) and, in the long-run, that would not be constructive.

[NastyCat4]

This isn't the peak? I don't see how that is possible, unless having 20 storms every season becomes the norm. I would say this season is a statistical anomaly in terms of number of storms, just as 1995 was. Every season has peaks and valleys in it, and this is clearly a peak.

In terms of intensity, there have always been years with extremely intense hurricanes. 1900, 1936, 1969, 1988, 1998, 2004, and 2005 had extremely intense storms--there are other years where there were "monsters" distributed randomly throughout.

It would be hard to see 2004-2005 as being anything but peak years, in terms of a statistical distribution .

[Dave C]

The West Pacific is much larger body of water with less land masses to disrupt storms. The environment in the Atlantic also tends to be more hostile than the West Pacific(this was told to me by a storm chaser who spent time chasing in West Pacific...Guam,Saipan,Okinawa.)Also, we have SAL which they don't deal with out in West Pac. Maybe you can add some of your thoughts Don on these 2 basins and their differences.

[donsutherland1]

Great point, LAwxrgal.

Also, the fact that this season is seeing the U.S. Gulf Coast barraged by landfalling hurricanes is not that surprising. Prior to the start of the season, a number of us here and elsewhere saw the evolution of a predominant pattern that would focus landfalls mainly in the Gulf region. What's happening is a product of that pattern.

Furthermore, the Tropical North Atlantic Index (TNA) has been running at record levels and this has allowed for higher oceanic heat content for possible tropical development/intensification. Given the neutral ENSO conditions, such tropical development has been explosive in terms of numbers. Right now, the Atlantic is running in a long-term warm cycle.

Overall, the mix of the synoptic pattern, Atlantic cyle, and neutral ENSO has converged for a catastrophic season for the U.S.

[donsutherland1]

Dave C,

Excellent points.

The overall environment has less shear per square kilometer in the West Pacific than the Atlantic, the West Pacific is much larger than the Atlantic Basin (Atlantic, Caribbean, GOM), and SAL effect coming off the North America is much less than that off Africa (much less desert area than north Africa, etc.).

Thus, the West Pacific sees far more tropical cyclone formation than the Atlantic basin.

[donsutherland1]

NastyCat4,

I was referring to the peak of the warm cycle not peak of tropical activity. personally, I believe we're near the peak of tropical activity in the current warm cycle if not there (average # of TCs per year). So overall I believe the comparison I made probably fairly states that one probably can't have much confidence in the study that argued that hurricanes are becoming more intense than in the past.

[x-y-no]

I haven't had a chance to read the Webster et. al. paper yet, but I've seen a synosis and I've read a couple of the other recent papers which suggest similar results.

You raise some valid issues, but I think there are some flaws in your analysis as well. The multidecadal oscillation is an Atlantic phenomenon, not a global one, wheras these studies looked at global data. Thus the distinction between the 70s and today is not nearly as significant as you suggest.

Regarding Dr. Gray's point about global activity, it's true that globally the frequency of storms has not increased, but the gist of these studies is that the cumulative power of tropical systems globally has increased quite dramtically.

Finally, I don't disagree in principle with your comments regarding politics, but I feel you're making a very unfair assumption that politics played a role in this research. I know it's a popular notion, but given the gravity of the charge I think it needs solid evidence to be made.

Some interesting discussion of this issue can be read here:

http://www.realclimate.org/index.php?p=181

[arcticfire]

Interesting , I like playing with %'s to make sure they say what I want too so I'll give it a shot.

You say that the 45-55 period say a more frequint escilation of hurricains to major. Thats true by your numbers but your numbers are deceptive.

45-55 : 42/115
95-05 : 43/156

True a greater % of the 45-55 made major , but only because 95-05 has had 36% more hurricains overall. In any case I dont' see this a great indication of anything either way as intensity of the cain is largly dependent on conditions around it , not what year it resides in. If anything the only thing these numbers show is that 95-05 has been 36% more active overall then 45-55.

Now your cat4 +. Here again you number just show that there are 30% more cat4+ hurricains in the 95-05 then in 45-55. You qualify this by saying 45-55 data might be flawed. Which brings up another point , you can't in one breath call 45-55 data flawed , and then in the next use it to prove your very specific number points.

So take your pick , use the 45-55 data to compare , in which case it onyl shows the current decade is more active in every aspect (8 more cat4+ , 1 more major , 41 more overall). Or dismiss the validity of the 45-55 data and don't use it to prove anything since it's unreliable.

[sponger]

Sorry Don, didnt mean to imply we have caused global warming. We are at the end of a 15K to 20K warm cycle. Most true research I have read indicates our contribution to warming has been negligible.

My point is if that changes, most of us wont pay attention because of the cry wolf scenario. The group that has pressed this agenda is mostly anti capitalists who focus on green house gases (industry) instead of methane which is a far worse problem. IMHO

[aerojad]

I'm sure there have been as many intense/numerous hurricanes in the past, but this is the first time a cycle like this has happened in the satellite age - where we can document it all - all the while having more people exposed to these storms (coastlines) worldwide than ever before as well. So from our vantage point, it's the worst we've "seen"... if that makes sense.

[chrisnnavarre]

"The strongest hurricanes in the present climate may be upstaged by even more intense hurricanes over the next century as the earth's climate is warmed by increasing levels of greenhouse gases in the atmosphere. Although we cannot say at present whether more or fewer hurricane will occur in the future with global warming, the hurricanes that do occur near the end of the 21st century are expected to be stronger and have significantly more intense rainfall than under present day climate conditions. This expectation (Figure 1) is based on an anticipated enhancement of energy available to the storms due to higher tropical sea surface temperatures.

The results described above are based on a recent simulation study carried out by Thomas R. Knutson and Robert E. Tuleya at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL). This study examined the response of simulated hurricanes to the climate warming projected for a substantial build-up of atmospheric CO2. Such an increase in the upper-limit intensity of hurricanes with global warming was suggested on theoretical grounds by M.I.T. Professor Kerry Emanuel in 1987. The latest GFDL investigation is the most comprehensive simulation study of the issue to date, making use of future climate projections from nine different global climate models and four different versions of a high-resolution hurricane prediction model. The hurricane model used for the study is an enhanced resolution version of the model used to predict hurricanes operationally at NOAA's National Centers for Environmental Prediction."

http://www.gfdl.noaa.gov/~tk/glob_warm_hurr.html

Gee, I don't know.....with names attached to that report like NOAA, and M.I.T. you tell me who has the agenda here???? I think we can all pretty much see who has the agenda, or maybe we can just sit and debate it a little while longer as we watch every major city along the coastal regions of the country be destroyed.

[gratefulnole]

How about taking into account that SAL has also been more persistent in recent years(possibly due to global warming) and it actually suppresses hurricane formation.

[donsutherland1]

Chrisnnavarre,

Again, as noted earlier, I do believe there is some contribution to the warming from human activity. I'm not in any way suggesting otherwise.

Moreover, in terms of intense hurricanes, it is fair to suggest what the models imply and prudent to take precautions for such a scenario e.g., building better flood protection, developing improved building codes, laying out more effective evacuation plans, etc.

My disagreement is not with forecasts per se, but with a specific conclusion based on a methodology employed in a single study--and only that study--that compared tropical activity during a warm cycle with a cold cycle and then generalized conclusions based on such a comparisons as if the longer-term Atlantic cycle didn't matter. I don't believe such comparisons are constructive and have serious reservations about the validity of that study.

Dr. Chris Landsea of the NOAA et. al., have also questioned the given conclusion that hurricanes are growing more intense from the specific study I have discounted.

[x-y-no]

My disagreement is not with forecasts per se, but with a specific conclusion based on a methodology employed in a single study--and only that study--that compared tropical activity during a warm cycle with a cold cycle and then generalized conclusions based on such a comparisons as if the longer-term Atlantic cycle didn't matter. I don't believe such comparisons are constructive and have serious reservations about the validity of that study.

Dr. Chris Landsea of the NOAA et. al., have also questioned the given conclusion that hurricanes are growing more intense from the specific study I have discounted.

This is a bit of a catch-22, though, because it is really only since the 70s that we have comprehensive global data on storm intensity throughout storm lifetime.

Kerry Emanuel's recent paper (discussed in the link I provided above) reaches a similar conclusion by different methodology, which is suggestive of some robustness to the conclusion.

And as I pointed out, the multidecadal oscillation you are referring to is an Atlantic phenomenon, whilst these studies look at the full globe.

[seaswing]

No doubt in my mind that they are more intesne and more frequent