Global warming has long been predicted to make hurricanes more intense. Well, now we are seeing more intense hurricanes. Chris Mooney has a great post on the recent storm surge of Category 5 hurricanes, now that Felix has joined that once-elite club. He notes:
- There have now been 8 Category 5 Atlantic hurricanes in the past 5 years (Isabel, Ivan, Emily, Katrina, Rita, Wilma, Dean, Felix).
- There have been two Atlantic Category 5s so far this year; only three other seasons have had more than one (1960, 1961, 2005).
- There have been 8 Atlantic Category 5 hurricanes so far in the 2000s; no other decade has had so many. The closest runner up is the 1960s with 6 (Donna, Ethel, Carla, Hattie, Beulah, Camille).
Some people, especially the Deniers, think this is all a coincidence, or the result of incomplete data from earlier years. Here's why I don't:
Global warming increases sea surface temperatures (SSTs), which are directly correlated with stronger storms. Indeed, tropical cyclones are threshold events -- if sea surface temperatures are below 80°F (26.5°C), they do not form.
Some analysis even suggests there is a sea surface temperature threshold close to 83°F needed for the spawning major hurricanes. Global warming may actually cause some hurricanes and some major hurricanes to develop that otherwise would not have (by raising sea surface temperatures above the necessary threshold at the right place or time). This is especially true in the Atlantic, where sea surface temperatures appear to be closer to the threshold than other hurricane-forming basins.
Equally important, one of the ways that hurricanes are weakened is the upwelling of colder, deeper water due to the hurricane's own violent action. But if the deeper water is also warm, it doesn't weaken the hurricane. In fact, it may continue to intensify. Global warming heats both the sea surface and the deep water, thus creating ideal conditions for a hurricane to survive and thrive in its long journey from tropical depression to Category 4 or 5 superstorm.
I have a longer discussion of this in Hell and High Water -- and a good nontechnical article can be found here. The bottom line is that we would expect global warming to increase the number of Category 5 storms. Indeed, a 2004 modeling study concluded:
One implication of the results is that if the frequency of tropical cyclones remains the same over the coming century, a greenhouse gas-induced warming may lead to a gradually increasing risk in the occurrence of highly destructive category-5 storms.
So the fact that we are seeing such an increase is no surprise.
Yes, it could all be a grand coincidence or the result of inadequate data -- but as a scientist I apply Occam's Razor. We have data that matches our theory. The simplest explanation is that the theory is right.
As NASA's James Hansen put it in an important 2007 analysis, "to the degree that hurricane intensification of the past decade is a product of increasing SST in the Atlantic Ocean and the Gulf of Mexico, human-made GHGs probably are a substantial contributor."
One final point: I am aware that the 2004 modeling study predicted it would be many decades before we saw the warming signal in hurricane intensity trends. You can take that as a sign that the data is wrong, if you want, but as I noted in "Are scientists overestimating -- or underestimating -- climate change? Part I," scientists have underestimated recent sea ice loss, ice sheet mass loss, temperature rise, sea-level rise, and expansion of the tropics.
So I conclude that a more likely explanation is that the models are systematically underestimating key climate-cycle feedbacks and omitting crucial factors that will accelerate the pace of climate change beyond what the IPCC "consensus" believes.
This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.
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Comments
View as Flat
Delay And Deny Posted 11:15 am
04 Sep 2007
...but you can't picke your hurricanes!
WAIT A MINUTE.
What about the LAST HURRICANE from a week ago, that went from a Cat 4 down to a Cat 1 and then became like a mist or a sun shower or something.
So, was global warming responsible for reducing that hurricane?
John Bailo
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kman Posted 1:25 pm
04 Sep 2007
The issue being discussed is how warmer SSTs (sea surface temperature, as you probably dont know what that is) increase the strength of hurricanes. Warmer land does not feed hurricanes, as that is probably gonna be your next comment. Learn your hurricane physics before you start your usual.
http://www.weather.com/newscenter/hurricanecentral/?from= ...
Check the link and look at the history so far. In the atlantic, we've already had 4 tropical storms and 2 hurricanes (both Cat 5), while in the Pacific we've had 5 tropical storms/depressions and 3 hurricanes. Ofcourse, the season has only started, and we still have a little under 3 months to go.
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Pete H Posted 3:55 pm
04 Sep 2007
Here is a link and a few select facts from an authoritative source.
http://www.aoml.noaa.gov/phod/amo_faq.php
What is the AMO?
The AMO is an ongoing series of long-duration changes in the sea surface temperature of the North Atlantic Ocean, with cool and warm phases that may last for 20-40 years at a time and a difference of about 1°F between extremes. These changes are natural and have been occurring for at least the last 1,000 years.
How much of the Atlantic are we talking about?
Most of the Atlantic between the equator and Greenland changes in unison. Some area of the North Pacific also seem to be affected.
What phase are we in right now?
Since the mid-1990s we have been in a warm phase.
What are the impacts of the AMO?
The AMO has affected air temperatures and rainfall over much of the Northern Hemisphere, in particular, North America and Europe. It is associated with changes in the frequency of North American droughts and is reflected in the frequency of severe Atlantic hurricanes. It alternately obscures and exaggerates the global increase in temperatures due to human-induced global warming.
How does the AMO affect rainfall and droughts?
Recent research suggests that the AMO is related to the past occurrence of major droughts in the Midwest and the Southwest. When the AMO is in its warm phase, these droughts tend to be more frequent and/or severe (prolonged?). Vice-versa for negative AMO. Two of the most severe droughts of the 20th century occurred during the positive AMO between 1925 and 1965: The Dustbowl of the 1930s and the 1950s drought. Florida and the Pacific Northwest tend to be the opposite - warm AMO, more rainfall.
How important is the AMO when it comes to hurricanes - in other words - is it one of the biggest drivers? Or Just a minor player?
During warm phases of the AMO, the numbers of tropical storms that mature into severe hurricanes is much greater than during cool phases, at least twice as many. Since the AMO switched to its warm phase around 1995, severe hurricanes have become much more frequent and this has led to a crisis in the insurance industry.
Does the AMO influence the intensity or the frequency of hurricanes (which)?
The frequency of weak-category storms - tropical storms and weak hurricanes - is not much affected by the AMO. However, the number of weak storms that mature into major hurricanes is noticeably increased. Thus, the intensity is affected, but, clearly, the frequency of major hurricanes is also affected. In that sense, it is difficult to discriminate between frequency and intensity and the distinction becomes somewhat meaningless.
If the AMO (in part) affects hurricanes - what drives the AMO?
Models of the ocean and atmosphere that interact with each other indicate that the AMO cycle involves changes in the south-to-north circulation and overturning of water and heat in the Atlantic Ocean. This is the same circulation that we think weakens during ice ages, but in the case of the AMO the changes in circulation are much more subtle than those of the ice ages. The warm Gulf Stream current off the east coast of the United States is part of the Atlantic overturning circulation. When the overturning circulation decreases, the North Atlantic temperatures become cooler.
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Billhook Posted 7:58 pm
04 Sep 2007
I notice that you post the (predictably Neo-con approved) output of NOAA
after excising its final para, that happens to acknowledge GW.
The final sentence of that para is as follows -
"In the 20th century, the climate swings of the AMO have alternately camouflaged and exaggerated the effects of global warming, and made attribution of global warming more difficult to ascertain."
This observation leaves wide open the critical issue of AGW impact driving the ongoing intensification of hurricane events.
Furthermore, NOAA post a graph of AMO showing average annual SST for the whole Atlantic as the basis of their assessment.
Which is of course evidently misleading, given that
the great majority of tropical storms are spawned not only during just a small fraction of each year,
but also within just a small percentage of the Atlantic area.
So, having seen the official censorship attempts at NASA,
why should we have any confidence in your selection of NOAA's output ?
Regards,
Bill
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Delay And Deny Posted 1:29 am
05 Sep 2007
Hurricanes return to historic patterns
http://www.sciencedaily.com/upi/index.php?feed=Science&am ...
NEW YORK, June 6 (UPI) -- A study by U.S. and Swedish researchers says the surge in major Atlantic hurricanes may not be tied to increasing global warming.
[...]
The researchers, who studied long cylinders of coral from reefs in the Caribbean, found that from 1730 there was an average each year of 3-3.5 major hurricanes. By the late 1960s, the frequency had fallen to 1.5 major hurricanes a year. The average between 1995 and 2005 jumped to 4.1 a year.
John Bailo
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Sam Wells Posted 3:04 am
05 Sep 2007
Dr. Gray just down-sized the 2007 hurricane season significantly from his May and June predictions. Still, records were broken this year with two Cat 5 hurricanes (Dean and Felix) and two double landfalls (Dean and Henriette).
If you check your facts, SST measurements this year were not as impressive as in 2005 or some previous years, speaking in terms of anomaly (departure from mean). As Dr. Masters of Weather Underground noted, one of the side effects of a hurricane is to significantly cool the ocean temperatures, since they stir up cold waters from the deep. Of course, a hurricane also warms up the atmosphere as well - temperatures over Dean and Felix at 10,000 foot flight levels were near 77 degrees, about 30 degrees warmer than normal for that altitude.
Simple answers, simple minds.
/sammie
Onward through the fog
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Pete H Posted 12:09 pm
05 Sep 2007
The last paragraph states that "the AMO is probably a natural climate oscillation." It further states "...the climate swings of the AMO have alternately camouflaged and exaggerated the effects of global warming, and made attribution of global warming more difficult to ascertain."
So I ask you, how in the heck do you show a link between hurricanes and global warming if the AMO is the only accurate predictor of hurricane frequency and intensity and its effects are such that they camouflage or exaggerate the effects of global warming?
It is irresponsible to state "hurricanes are getting stronger - thanks to global warming." That theory simply isn't supportable at this time given what we know about the effect of the AMO on hurricanes and how little we really know about long term climate change.
I guess "difficult to ascertain" means "proof of a link" to some folks.
Here is that last paragraph:
Instruments have observed AMO cycles only for the last 150 years, not long enough to conclusively answer this question. However, studies of paleoclimate proxies, such as tree rings and ice cores, have shown that oscillations similar to those observed instrumentally have been occurring for at least the last millennium. This is clearly longer than modern man has been affecting climate, so the AMO is probably a natural climate oscillation. In the 20th century, the climate swings of the AMO have alternately camouflaged and exaggerated the effects of global warming, and made attribution of global warming more difficult to ascertain.
We do not talk -- we bludgeon one another with facts and theories gleaned from cursory readings of newspapers, magazines and digests.
Henry Miller
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