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Irene’s Potential for Destruction Made Worse by Global Warming, Sea Level Rise

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UPDATED BELOW

We're now a day out from Hurricane Irene’s projected landfall in the Outer Banks of North Carolina (or near-miss, and it doesn’t make a lot of difference which it is). A day later — sometime Sunday, that is — the storm’s assault on the New York metropolitan area will begin. And unless Irene’s track veers sharply and unexpectedly out to sea, the Northeast will suffer its worst hurricane in decades. Evacuations have begun from Cape Hatteras all the way up to New Jersey; in New York City, hospitals and nursing homes in low-lying areas in Brooklyn and Staten Island have begun emptying, and the city’s subway system could shut down entirely on Saturday, for safety reasons.

At the moment, the immediate question for anyone in the path of the storm is — or should be —  “how can I keep myself and my loved ones safe?” But another question may be lingering in the background. It’s the same question that came up in April, when a series of killer tornadoes tore up the South in April, and in May, when floods ravaged the entire Mississippi River basin, and in July, when killer  heat waves seared the Midwest and Northeast, and in August, when Texas officially completed its worst one-year drought on record — a drought that isn’t over by a long shot.

The question: is this weather disaster caused by climate change?

Wrong question.

Here's the right question: is climate change making this storm worse than it would have been otherwise?

Answer: Absolutely

For one thing, sea-surface temperatures in the Atlantic Ocean are higher now than they used to be, thanks to global warming, and ocean heat is what gives hurricanes their power. All other things being equal, a warmer ocean means a more powerful storm. It’s hard to say that all other things are exactly equal here, but it’s certainly plausible that Irene would have been a little weaker if precisely the same storm had come through, say, 50 years ago.

What we know for sure, however is that thanks largely to climate change, sea level is about 13 inches higher in the New York area than it was a century ago. The greatest damage from hurricanes comes not from high winds and torrential rains — although those do cause a lot of damage. It’s from the storm surge, the tsunami-like wall of water a hurricane pushes ahead of it to crash onto the land. It was Hurricane Katrina’s storm surge, not the wind or rain, that destroyed New Orleans back in 2005.

With an extra foot of sea level to start with, in other words, Irene’s storm surge is going to have a head start. And climate change is a big part of the reason why.

UPDATE:

The relationship between climate change and hurricanes is one that scientists are still trying to understand. As I mentioned above, warm ocean waters provide the energy that keeps a hurricane going. That's why the storms lose energy when they pass over land, and why they gain energy when they pass over warmer water (as Katrina did when it entered the Gulf of Mexico after crossing Florida). 

Still the phrase "all other things being equal" is key. In a warming climate, all other things will not necessarily be equal. For one thing, wind patterns will probably change, and something called wind shear, which tends to snuff out hurricanes before they can fully form, may increase over the Atlantic as the climate changes. Moreover, some climate scientists argue that a key factor in hurricane formation is not simply the ocean temperature, but the differences in temperature from one ocean basin to another. One recent paper in Science concludes that the overall number of hurricanes in the Atlantic is likely to decrease over the coming century — but that the intensity of those that do happen is likely to increase.

But that says nothing — and nobody has a clue — about how many of those hurricanes will hit land, and if they do, whether it will be in densely populated areas or not (although more and more of the U.S. shoreline that lies in hurricane territory is filling up with people). 

Nevertheless, one study has projected an overall 20 percent increase in hurricane-related damage based on population growth and sea-level rise alone, even if there were no change in hurricane frequency or strength.

Let's also not forget that while storm surges pose the biggest danger, Irene will almost certainly bring torrential rains to a part of the country that has already been drenched over the past couple of weeks. With saturated ground and a deluge that could add up to 10 or even 20 inches of rain in just a day or so, rivers and creeks will likely overflow their banks, causing widespread flooding. And then there's the wind, which will inevitably cut power to hundreds of thousands of people, at least (it can happen even when there isn't a hurricane).

To better understand how climate change-related sea level rise aggravates coastal flooding risks, see this graphic we produced based on 2010 Census and sea level rise data. For those who want to monitor Irene's progress, here's a map, a great liveblog, and the main tracking portal from the National Oceanic and Atmospheric Administration. You can also get updates by following us on Twitter at @ClimateCentral. Our managing editor Andrew Freedman, who also writes for the Washington Post's Capital Weather Gang blog, will be tweeting storm updates throughout the weekend via @afreedma. 

Comments

By BobN
on August 26th, 2011

Michael - Not sure what seal’s you are talking about in the title (might want to fix that, though it did give me a chuckle).

As to the impact of global warming on the strength of the storm, I think the answer is more of a “possibly” than an an “absolutely”.  Yes, SST are warmer than average this year, but the past New England storms (e.g., 1938) were plenty powerful.  What is unique is the storm track, which I understand is more a function of current meteorological conditions (Bermuda high and Eastern US high funneling the storm up the coast.  Whatever the cause or possible impact of global warming, as a NJ resident, this is the first time I have been very concerned about significant local impacts from a hurricane.

Reply to this comment

By Stephen Balbach (20861)
on August 26th, 2011

High tide in Manhattan will be 8am Sunday at 5.3 feet, one of the highest tides of the month. (Monday is the new moon, which determines the highest monthly tides.) Currently Irene is forecast to be off Delaware at 8am, which is pretty close to NYC, but the speed keeps changing so it may be even closer (or further). In any case the tides are looking to be a major factor in this event wherever you are. Thanks, moon!

http://www.saltwatertides.com/

Reply to this comment

By No Whining (19966)
on August 27th, 2011

Oooo! New York, Center of the Known Universe might take one on the snout! Now the suffering is real! Now it is intense! Now the Concernometer pegs out at 11! (Not like when you peasants elsewhere get hit, you pansies.) Shouldn’t you be out surfing in this? You have the mental capacity for it.

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By Eduardo Ferreyra (Córdoba, Argentina 5101)
on August 28th, 2011

Back in 1988, James Hansen scared Congress telling senators that by 2000 sea level would have grown so much that Riverside Ave would be covered with water. So predictions about sea level rises must be taken seriously without any clown making absurd claims. SST have not risen lately, data show that they have even decreased a little ”“as sea levels have in many parts of the world, not by subsidence but by actually going down as is the Maldivas Islands case in the Indian Ocean. And Ocean Heat content has evidently gone down. Also global ACE (Accumulated Cyclonic Energy) has gone down to its lowest point in 35 years, indicating that hurricanes, typhoons, cyclones, etc are now weaker than 35 years ago. Check here: http://coaps.fsu.edu/~maue/tropical/

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By M (20008)
on August 28th, 2011

The way I see it, climate change has the following impacts on hurricanes, in approximate order of how well understood they are:

1) increased sea level rise means higher storm surge.
2) increased temperatures probably mean more precipitation from a given storm… I know this is robust for standard storms (eg, we’ve already seen an increasing trend in the proportion of heavy precipitation events), I assume this applies to hurricanes as well.
3) increased intensity of a given storm due to increased sea surface temperatures (possibly compensated for by changes in wind shear): because storms are changed by a number of factors, this one is likely but not sure.
4) small change in frequency of storms, uncertain sign: I believe that the latest science indicates that climate change is more likely to decrease frequency of storms than increase them (due to wind shear), but this is quite uncertain.
5) possible decrease in landfalling storms? I’ve seen I think one study which suggests that the region of the Atlantic which generates landfalling US storms is where changes in wind shear/dust/etc. are most likely to reduce storm frequency… but this is very uncertain.

Overall, the increased sea level, precip, and intensity I think outweigh the less certain indications of reduced frequency and landfalls… but it is complicated.

-M

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By M
on August 28th, 2011

Eduardo Ferreyra is sadly confused. Hansen’s 1988 testimony is here: http://image.guardian.co.uk/sys-files/Environment/documents/2008/06/23/ClimateChangeHearing1988.pdf: and it stands the test of time pretty well in my opinion.  This testimony makes no statements about sea level rise. Ferreyra is probably thinking about an interview that Hansen apparently gave to Bob Reiss (also in 1988), which regarding the hypothetical case in which CO2 were doubled (which it isn’t, yet), and a time period of 40 years (so 2028, not 2000). See footnote 1 in http://www.columbia.edu/~jeh1/mailings/2011/20110126_SingingInTheRain.pdf.

SST continue to rise (modulo ENSO variability): http://www.cru.uea.ac.uk/cru/data/temperature/hadsst2gl.txt. 2010 was the 3rd highest SST on record after 2003 and 1998. But the last half of 2010 was part of the strongest la Nina in the past several decades, with a much lower average MEI index than either 2003 or 1998 (http://www.esrl.noaa.gov/psd/enso/mei/table.html) - and while the SST long term trend is clearly up, it is well known that sea surface temperatures are very sensitive to La Ninas (cooler) and El Ninos (warmer).

And sea level continues to rise: http://sealevel.colorado.edu/.  (Unless, by “gone down recently” Ferreyra really meant to say “has paused in its rise, but is still above any sea level recorded before 2006”.

It is a pity that misinformation is so easily believed and spread by those who don’t want to accept reality.

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