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New Study Ties Hurricane Strength To Global Warming

One of the major unanswered questions about climate change is whether hurricanes have become more frequent and stronger as the world has warmed. Until now, there hasn’t been enough evidence to settle the question, but a report published Monday in Proceedings of the National Academy of Sciences may have changed all that. Using an entirely new method of tallying hurricane power and frequency, a team of scientists say that hurricanes are, indeed, more of a danger when ocean temperatures are higher. “In particular, we estimate that Katrina-magnitude events have been twice as frequent in warm years compared with cold years," the report says.

Until now, the problem with such calculations is that until satellites came along in the 1970’s, nobody knew for sure how many hurricanes formed during a given year. That’s because some hurricanes never strike land, and unless a ship or a plane happened upon one of these storms, nobody might even know it had ever existed, and certainly not how strong it was.

Credit: flickr/NASA Goddard Space Flight Center

The record from the '70's onward is much more complete — but since hurricane numbers wax and wane based on a natural cycle, that’s not long enough to see if there’s a warming-related pattern on top of ordinary fluctuations. Ocean temperatures fluctuate according to natural cycles as well, although studies have shown an overall increase in North Atlantic sea surface temperatures, a trend that has been linked to manmade global warming.

But Alex Grinsted of the University of Copenhagen and his colleagues came at the problem in an entirely different way. They looked not at hurricanes themselves, but at the storm surges tropical storms drive before them as they come ashore, and surges have been reliably measured by devices known as tide gauges all the way back to the 1920's.

“Using surges as an indicator,” Grinsted said in an interview, “we see an increase in all magnitudes of storms when ocean temperatures are warmer.” As ocean temperatures have risen inexorably higher in the general warming of the planet due to human greenhouse-gas emissions, the scientists concluded, hurricane numbers have moved upward as well. The implication: they’ll keep increasing along with global temperatures unless emissions are cut significantly.

There’s one obvious caveat about the new results: not every hurricane creates a storm surge, since they don’t always hit land. And not every storm surge is caused by a hurricane. “The storm surge index,” Grinsted said, “is sensitive to strong winter storms as well.” And it’s quite possible, he said, that the intensity of a given storm surge could be made greater or less by the angle at which a hurricane hits land.

Surges aren’t, in short, a perfect stand-in for hurricanes, but Grinsted said that they’re pretty good. In cases where they could do so, the team has lined up hurricane data with surge data, and, he said, “there are clear correlations. So while our paper might not explain everything, it is still useful."

Credit: flickr/Ana Rodríguez Carrington

In fact, Grinsted said, storm surges are more relevant to peoples’ lives than hurricanes. “Surges are one of the most damaging aspects of hurricanes,” and that’s going to become increasingly true as sea level continues to rise over the rest of this century. “If we want to talk about threat and risk, then this could be a more important measure,” Grinsted said.

Since it measures hurricanes indirectly, the paper is likely to prove controversial, said Kerry Emanuel, an MIT climate scientist who has done extensive research on the hurricane-climate connection (he also served as editor for the PNAS paper). “It’s a legitimate piece of research,” he said in an interview, “but it won’t convince everyone.”

That much is clear from comments other scientists have made after reading Grinstead's paper. "Although they have shown a correlation between their surge index and measures of hurricane activity," said Gabriel Vecchi, of NOAA's Geophysical Fluid Dynamics Laboratory in New Jersey, in an email, "it is far from a 1:1 relationship."

That, plus the fact that surges depend on angle and other factors, leaves Vecchi underwhelmed. Tom Knutson, another GFDL scientist, has a second worry. "The start date in 1923," he said, also by email, "is a relatively low period in landfalling and basin-wide hurricane/or tropical storm time series with relatively higher activity in the late 1800s." His point: if you start during unusual lull, it's not surprising that you get what looks like a significant increase afterward.

But Emanuel is still impressed, in part because he thinks the technique Grinsted and his collaborators used is so enormously clever. “I kick myself,” he said, “for not having thought of it myself.”

Related Coverage
Hurricane Isaac Spurs Design of Storm Surge Warnings
Putting the Eyes of the Crowd on the Eye of Hurricanes
NASA Drones to Spy on Hurricanes, Storm Intensity
Hurricane Tracks: 10 Recent Major Storms to Hit the U.S.

Comments

By mememine69 (54434)
on October 15th, 2012

Science has never said it will happen, only might happen. Do we WANT this misery to be real?

REAL planet lovers are glad a crisis was exaggerated.

Science says we are at the brink “maybe” yet they still refuse to say any crisis “will” happen. Not one single IPCC report of crisis is without “could be” and “likely” etc.

HELP MY HOUSE IS ON FIRE, MAYBE?

And get up to date:
*Occupywallstreet does not even mention CO2 in its list of demands because of the bank-funded carbon trading stock markets run by corporations.
*Obama has not mentioned the crisis in the last two State of the Unions addresses.
*Julian Assange is of course a climate change denier.
*Canada killed Y2Kyoto with a freely elected climate change denying prime minister and nobody cared, especially the millions of scientists warning us of unstoppable warming (a comet hit).

Romney will thank us for fear mongering more votes his way.

Reply to this comment

By Etaoin Shrdlu (Williamsburg, VA 23187)
on October 15th, 2012

LOL!  Government data shows that the frequency strength of hurricanes has been decreasing while global warming has been increasing!

Reply to this comment

By Henry
on October 18th, 2012

has an excellent article entitled “Scary Pictures” that tells of the problems with always exaggerating outcomes in scientific debates. He says;

” Campaigners on important but complex issues, annoyed by the length of time required for public deliberations, often react by exaggerating their claims, hoping to force a single solution to the forefront of public debate. But, however well intentioned, scaring the public into a predetermined solution often backfires: when people eventually realize that they have been misled, they lose confidence and interest.
When scare tactics replace scientific debate, whether about GM crops or climate change, nothing good can come of it. We all deserve better.”

Climate campaigners need to pay attention to this though I believe it’s already way too late for that. People aren’t stupid, they remember the claims that never happen and after a while all this scare mongering goes in one ear and out the other.

Reply to this comment

By Christopher Squire (Twickenham)
on October 18th, 2012

‘One of the major unanswered questions about climate change is whether hurricanes have become more frequent and stronger .  . ‘

This is TWO questions not one as frequency and strength are independent variables.

Reply to this comment

By Constance (Chgo., Il. 60660)
on October 29th, 2012

I’m not a scientist, nor even a full college grad.  But I do have my instincts, and they are never wrong.  I don’t really listen to much outside of that.  I am not an easily scared person either.  All of the retoric done by all the different factions Iv’e encountered & read & viewed in the last ten years has been (in my humble opinion) very,  very interesting.  Yet, actons still speak louder than words.  I sence many of us Americans have lost sight of that.  Mother Earth will have the last word and I think we’d all better start listening to her.  Now is not the time to argue, just follow your heart & do what’s there.

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By Minoo Netervala (Los Angeles, Ca.90034)
on October 29th, 2012

I completely agree with you on cimmate change

Reply to this comment

By Christine L.Cikan (Anchorage, Alaska 99507)
on October 30th, 2012

At age twenty I was lamenting the expotential growth of the population. That was forty years ago. Any check of our culture back then showed signs of future catastrophic events due to stresses on Mother Earth. Something as routine as McDonalds growth rate predicted a world imploding. I dropped many small phrases around,“the animals doom is our doom”, you can’t sully where you eat and “we are the aliens!” Really, they don’t want to hear it. At age sixty two, it is my realization that we are doomed. If Al Gore could not bring awareness and most importantly, change, then what can the rest of us do. The more important this issue becomes, the more it will be used as a tool by our enemies. Monsantos, Middle East Terrorists, hunters, corporations have actually gained strength. Am shocked by even wasting my time addressing this subject after forty years of trying to sway people. Seems like folks have gotten worse in their consumption, denial and disregard of the envoirment and the creatures that are dying within it. System after system is crashing. Many people have sounded the alarm but few are listening and even fewer are willing to change. So sorry.

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By Mark Hanisee (Riverside,Ca. 92506)
on October 31st, 2012

Climate change deniers are decreasing,  no dought due to the increasing trainwrecks of freaky weather.  We can’t quit Ms. Cikan, we must make it a lifelong effort; the Koch brothers would smile if we pack it in.  We don’t have a 150 years like civil rights or womens rights but the struggle must continue for future generations and this remarkable planet.  I think people look at me as being less bat shit crazy and are listening a little more, but wouldn’t swear to it.  I am 63 and share your isolation but we must continue to educate and elect people who will carry this fight.  I realize Sara Palin fantisizes this is God’s warning whenever their is a disaster.  Lets shut her up!! There is a history of people struggling to advance civilization and I feel a kinship to them.  The greedheads not so much. Many will try to do the right thing just because. That"s us. Solidarity.

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