TCS Daily


Global Warming Not Featured in New Hurricane Study

By Patrick Michaels - March 16, 2006 12:00 AM

The latest Science magazine features a paper linking increasing sea-surface temperatures to global increases in the most severe hurricanes, but it does NOT mention global warming as the cause. Think the newspapers won't?

Over the last few decades, hurricane climate experts have largely eschewed linkages between global warming and increases in the number or strength of hurricanes. That is, until late last summer, when a series of highly publicized papers claimed otherwise. The papers pointed out that sea-surface temperatures (SSTs), the essential fuel of hurricanes, have been increasing in the primary hurricane-development regions pretty much globally since 1970 (the start of global satellite hurricane track and intensity records). Over that time, hurricane intensities have also been on the rise. And since global warming causes SSTs to rise, that must be the cause of the recent spate of strong hurricanes.

The problem with this logic is that hurricanes require a very specific environment to flourish. High SSTs are a necessary but not sufficient condition to spin up strong storms. It is also important that there be very little change in the winds with height; that near surface winds blow in such a manner to cause moist air to gather near the storm's center; and that temperatures decline rapidly with height to promote a very unstable atmosphere, among other factors. One criticism of the studies from last summer is that the focus was almost entirely on SSTs only. In order properly to link hurricane trends to SSTs (and global warming), you need to discount trends in these other, critical variables.

This week's Science paper by Hoyos, Agudelo, Webster and Curry again uses data on global hurricane intensity since 1970. They report that the global increase in category 4 and 5 hurricanes is linked to SST but not any of the other factors.

The authors base their case on the observation that SSTs are increasing in all ocean basins over the period of record, but the other key hurricane-development variables they examined do not show consistent relationships across the same basins. For example, in the six ocean basins they examined, the authors found a significant increase in atmospheric moisture levels in the East Pacific only, and vertical wind shear (the change in wind height) only weakened significantly in the North Atlantic (more on this observation later).

Let's look at their results more carefully. Figure 1 shows the trend in an index of "moist static stability." Essentially, strong hurricanes can more easily form when this index value is low. In five of the six ocean basins, the authors find a statistically significant decline in moist static stability. But it's especially interesting to note that climate models (run under scenarios of increasing carbon dioxide) are also consistent in their forecasts of temperature changes in the lower atmosphere. They all report that the atmosphere will become more stable (e.g., Knutson and Tuleya, 2004). But that's the opposite of what's shown in Figure 1. So the only way to make the case that these changes are carbon dioxide-induced is to ignore the climate models, and who's willing to step forward and do that?


Figure 1. The trend in a measure of atmospheric stability (the more positive the index, the more stable the atmosphere). A more unstable atmosphere is better for hurricane intensification. The downward trend evident in five of the six tropical cyclone basins indicates that almost uniformly, conditions are getting better for producing more strong storms. Universally, climate models run with increasing carbon dioxide level predict the exact opposite behavior (source: Hoyos et al., 2006, Supplementary Material)

An examination of the number of category 4 and 5 storms from 1945-present shows that we are indeed currently experiencing a high frequency of major storms. But recent years are comparable to another fairly active period in the late 1950s and early 1960s. The aforementioned Science papers only considered the period from 1970 onward, because those data are believed to be the most accurate and internally consistent. However, the long term data from both the Western Pacific and the North Atlantic (the world's two most active regions) are reasonably good, especially with respect to the number of strong storms, which are obviously more likely to be detected.


Figure 2. The number of category 4 and 5 hurricanes observed in the Western Pacific (top) and North Atlantic (bottom) oceans since 1945. The counts in recent decades are not so much different than the counts in the 50s and 60s.

Another factor in the recent spate of strong storms is a long-term cycle in SSTs. In the Atlantic, for example, all hurricane researchers are aware of the Atlantic Multi-decadal Oscillation (AMO), a somewhat periodic cycling between high and low SSTs in the North Atlantic, including the primary hurricane formation zones. Figure 3 shows one of several incarnations of the AMO. Note the clear tendency toward positive AMO values beginning in the late 1960s. There were a lot more strong hurricanes from the 1940s through the mid-1960s (positive AMO), which was followed by a quiescent period (negative AMO). Any evidence of increasing SSTs based on a data set that begins around 1970 will identify an artificial trend that is really part of a longer-term cycle. The Science authors had perfectly legitimate reasons to begin their analysis in 1970, but a broader perspective is needed before you can call that increase a global warming signal.


Figure 3. Time series of the Atlantic Multi-decadal Oscillation (AMO). Again, notice a big trend since 1970, but nothing unusual in the long term (source: Knight et al., 2005).

With respect to North Atlantic hurricanes, an interesting paper was just published by Jyotika Virmani and Robert Weisberg in Geophysical Research Letters. One reason SSTs can build up is the lack of evaporation, as evaporation plays a big role in cooling ocean surface waters. Virmani and Weisberg showed that in 2003, 2004 and 2005, the position of the Bermuda High pressure system shifted from its mean position, forcing much weaker trade winds in the primary hurricane development region. Weaker winds mean less evaporation and higher SSTs. They also calculated that most of the 1-2 degrees celsius warming of ocean waters observed can be accounted for by the observed slackening of the trade winds. And when they examined the long-term pattern of trade winds in this region, the winds began weakening in 1970.

A major hurricane is a very unique event — a lot of disparate factors must become organized in just the right way to allow a major storm to develop. While high SSTs are one critical ingredient, they alone are insufficient to generate a whopper storm. SSTs have been increasing since 1970, as have major hurricanes, but the connection is not nearly as simple as some authors are suggesting. And careful scrutiny of ALL of the available data shows the connection to global warming is less than tenuous.

References:

Hoyos, C.D., et al., 2006. Deconvolution of the factors contributing to the increase in global hurricane intensity. SciencExpress, March 16, 2006.

Knight, J.R., et al., 2005. A signature of persistent natural thermohaline circulation cycles in observed climate. Geophysical Research Letters, doi:10.1029/2005GL024233.

Knutson, T., Tuleya, R., 2004. Impact of carbon dioxide-induced warming on simulated hurricane intensity and precipitation: Sensitivity t the choice of climate model and convective parameterization. Journal of Climate, 17, 3477-3495.

Virmani, J.I., and R. H. Weisberg, 2006. The 2005 hurricane season: An echo of the past or a harbinger of the future? Geophysical Research Letters, doi:10.1029/2005GL025517.

Webster, P.J., et al., 2005. Changes in tropical cyclone number, duration, and intensity on a warming environment. Science, 309, 1844-186.

Categories:

27 Comments

Here comes the spin, here comes the spin.
'...The team's findings are controversial because they draw a connection between stronger hurricanes and rising sea surface temperatures—a phenomenon that has itself already been linked to human-induced global warming.

The study by Curry and her colleagues therefore raises the frightening possibility that humans have inadvertently boosted the destructive power of one of Nature's most devastating and feared storms.

"If humans are increasing sea surface temperatures and if you buy this link between increases rising sea surface temperatures and increases in hurricane intensity, that's the conclusion you come to," Curry said."

http://www.livescience.com/forcesofnature/060316_hurricane_sst.html

long term
In a world in which 20 to 30 year, and longer patterns have been found regarding hurricane strength and frequency.
Any study that covers only 30 years is immediately suspect.

Spin & Shear
Research Re-examines Strong Hurricane Studies
Georgia Institute of Technology, March 16, 2006

...Last summer, the journals NATURE and SCIENCE published studies claiming to show a very strong link between rising tropical sea surface temperatures and an increase in the strength of hurricanes. The Nature study, by Kerry Emanuel at the Massachusetts Institute of Technology, concluded that cyclonic storms in the North Atlantic and North Pacific oceanic basins were increasing in strength and duration. That increase, Emanuel concluded, was DUE TO INCREASED SEA SURFACE TEMPERATURES caused, in part, by global warming. A month later, the journal Science published research linking an increase in sea surface temperatures over the past 35 years to a near doubling in the number of the strongest hurricanes, those labeled Category 4 or 5...

This latest study sought to determine whether factors other than sea surface temperatures could be significantly contributing to this 35-year trend. Georgia Tech researchers Carlos Hoyos and Paula Agudelo, along with Curry and Webster examined three factors: vertical wind shear (changes in wind speed and direction with height); humidity in the lower atmosphere; and zonal stretching deformation, which is the tendency of the winds to rotate in a cyclonic direction.

"If you examine the intensification of a single storm, or even the statistics on intensification for a particular season, factors like wind shear can play an important role," said Curry, professor and chair of the School of Earth and Atmospheric Sciences at Georgia Tech. "However, THERE IS NO GLOBAL TREND IN WIND SHEAR OR OTHER FACTORS over the 35-year period."

http://www.physorg.com/news11855.html

If this held any water ...
If this held any water, you would be able to publish it in a science journal instead of on a web site dedicated to denial.

It's settled
Every weather anomoly can now be attributed to too much CO2.
Let's talk about something else.

Why was it so warm 1000 years ago?

As you see
LG can't refute anything in the study, so he dismisses it out of hand.

Typical.

In LG's corner of the world
Hoyos, C.D., et al., 2006. Deconvolution of the factors contributing to the increase in global hurricane intensity. SciencExpress, March 16, 2006.


Knight, J.R., et al., 2005. A signature of persistent natural thermohaline circulation cycles in observed climate. Geophysical Research Letters, doi:10.1029/2005GL024233.


Knutson, T., Tuleya, R., 2004. Impact of carbon dioxide-induced warming on simulated hurricane intensity and precipitation: Sensitivity t the choice of climate model and convective parameterization. Journal of Climate, 17, 3477-3495.
Hoyos, C.D., et al., 2006. Deconvolution of the factors contributing to the increase in global hurricane intensity. SciencExpress, March 16, 2006.


Knight, J.R., et al., 2005. A signature of persistent natural thermohaline circulation cycles in observed climate. Geophysical Research Letters, doi:10.1029/2005GL024233.


Knutson, T., Tuleya, R., 2004. Impact of carbon dioxide-induced warming on simulated hurricane intensity and precipitation: Sensitivity t the choice of climate model and convective parameterization. Journal of Climate, 17, 3477-3495.


Virmani, J.I., and R. H. Weisberg, 2006. The 2005 hurricane season: An echo of the past or a harbinger of the future? Geophysical Research Letters, doi:10.1029/2005GL025517.


Webster, P.J., et al., 2005. Changes in tropical cyclone number, duration, and intensity on a warming environment. Science, 309, 1844-186.

--------------------


None of the above named journals count as science journals.
I guess because they don't exclude contrary articles, like the ones LG approves of do.

the long-term perspective
Hunting Prehistoric Hurricanes (http://www.sciencenews.org/articles/20000520/bob9.asp)

"There are millennial-scale variations in hurricane activity. Our data suggest that there are much longer cycles superimposed on the decadal cycles," says Liu. "We've had a quiet period, an active period, and for the past 1,000 years, we're back to a relatively quiet period."

"Indeed, the data indicate that catastrophic hurricanes struck the Gulf Coast much more frequently 1,000 to 3,500 years ago than they do now. During that hyperactive period, such storms hit the area from four to five times more often than they have in the past 1,000 years."

two years of hurricanes does not a trend make
look at figure 2. the entire hysteria over hurricanes has been triggered by a high number of strong storms over the past TWO years. the GW freaks don't even need a 30-year study; two years is enough to proclaim the end of the world as we know it. and never mind the figure that shows pretty much no statistical change in the western pacific, that apparently doesn't count.

there might be something to global warming, even though it's hard to say for sure with so many other variables at work. so yeah, we might have to deal with stronger hurricanes in the future, which will be easier to do in a technologically growing economy rather than by reverting to the stone age. but for the GW extremists, that's not even the issue. the important thing for them is to find ANY empirical evidence of ANYTHING different as a result of GW, and then go all hysterical over it to assuage their pathological self-loathing.

A new study
John Christy and colleagues at the University of Alabama at Huntsville in the Journal of Climate have studied Californias Central Valley and have concluded that the warming seen there is most likely the result of land use changes, and not changes in greenhouse gases.

The 30 Day Michaels Forecast
The passage of the next war front through the peer reviewed literature will precipitate a new low in TCS headlines as Pat's heavy thumb on the bogus graph scales photoshops the truth into oblivion amidst heavy downpours of scientific misrepresntation.
In the wake of the Micheals front, flurries of cant and occasional scattered howlers will descend like curtains of fog in this discussion column.

Time and Frequency
Too right MTG. As the good doctor Brignell would say, the authors have accurately located the hurricane trend in the time domain but have no idea of its location in the frequency domain.

So much for peer review
http://climatesci.atmos.colostate.edu/2006/03/16/conflict-of-interest-in-the-ccsp-report-temperature-trends-in-the-lower-atmosphere-steps-for-understanding-and-reconciling-differences/

Details how CCSP asked the scientists who created the research, to do the review of that research.

Kitchen Sink Featured in New Fox TV rebutal
Sorry. Too busy reading Davidson & Jannsens, Nature 440;165-173
do let us know what you think of it . I'm sure Pat will have a sound bite before long.

Just when you think you are starting to understand the weather
"Flying cow leaves two police cars in flames"

http://www.woai.com/news/local/story.aspx?content_id=EE418016-0667-4C62-9602-0C699962154F

I'm sure Russell actually thinks he said something funny.
But to the rest of us, it looks like he's making an ass of himself.

What you mean 'we'?
Er, Mark, no one else is reading you.
To encounter the non-eitorial 'we', proceed to the bottom right of the ed page of this tuesday's Wall Street Journal.
Bye.

mighty full of yourself
So you claim that I am the only person in the world who holds this opinion of you?

Mark reminds you it's too simple to be understood
For a more coherent acount try :
http://www.realclimate.org/index.php?cat=10

The article you cite
Reading the article you link to, I notice the record reveals nine cat 4 or 5 storms during an 1100 year period. This doesn't sound to me like evidence of a past active period, as it is a bit less than one per century. I think the thesis needs more work.

Russel reminds you that
liberals have had their sense of humor surgically removed.
Which explains why they are so mad all of the time.

QED
Congratlations on confirming your own hypothesis by failing to attract any additional readers.
Now go read Real Climate like a good fellow.

Michaels is funded by the fuel industry
Ahem, I think our friend, the author, should disclose that he has received over $160,000 in funding from the fuel industry. At least, that's what I would do, if I was writing an stock article that spoke of future gains in MSFT, after I received a large payment from Microsoft.

It's an integrity thing. Just so we know why he chose to oppose thousands of scientists who all agree that global warming is not just a figment of our imagination.

Look at all of what's happening
If you look at hurricanes alone, of course that is not enough evidence to draw any conclusions whatsoever. But, rise in hurricane frequency is not the only thing that's happening now. Bird's are migrating to the south later, mating seasons are sooner, caterpillars are changing into butterflies even sooner than that, glaciers are disappearing, ice shelves are retreating, tornadoes are more frequent, cyclones are now forming in the south pacific, and the list goes on.

I feel like we're reliving the monkey trials all over again, where one side is completely blind to the possibility that Man evolved from Ape.

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