What We Can and Can't Say About Global Warming and Hurricane Dean

Hurricane Dean at landfall early this morning, image courtesy of the Weather Underground.

Now we see why the ancient Mayans built their cities inland from the coasts.

Early this morning, Hurricane Dean slammed the Yucatan as a still-intensifying Category 5 storm with sustained winds upwards of 165 miles per hour. Dean required some troubling readjustments of our hurricane records, and as a result, we may hear some serious chatter today about the relationship between these intense storms and global warming.

For that reason, the purpose of this post is to lay out what we can and can't reliably say about Hurricane Dean. The upshot is this: We have to be careful what we claim and how we claim it, but even so, Dean fits into a worrisome pattern.

Here are the key records that Dean either broke or otherwise affects:

1. With a minimum central pressure of 906 millibars, Dean was the ninth most intense hurricane ever observed in the Atlantic basin (for comparison Hurricane Katrina's minimum pressure was 902 millibars).

2. That 906 millibar pressure reading was at landfall, making Dean the third most intense landfalling hurricane known in the Atlantic region and the first Category 5 storm at landfall since 1992's Hurricane Andrew.

3. When measured by minimum pressure, six of the ten most intense Atlantic hurricanes--Wilma, Rita, Katrina, Mitch, Dean, and Ivan--have occurred in the past ten years.

We can't blame any one hurricane event on global warming directly. Nevertheless, the information above is certainly consistent with the idea advanced by some scientists that global warming is causing an intensification of the average hurricane. We're apparently seeing the strongest hurricanes recur in the Atlantic with a higher frequency than before -- or at least, than we've ever been able to measure before.

Measuring systems weren't as good in earlier eras, you see -- a fact that makes our records somewhat impeachable. A "record" is only what's recorded, after all. And so skeptics will inevitably quibble with our imperfect data and challenge it. There might well have been a storm much stronger than Dean 200 years ago -- we just don't know.

Nevertheless, if you look at the data we have, Dean fits into a very troubling pattern and context. Moreover, the present data, with all their admitted imperfections, aren't all we have to go on. There's also the theoretical expectation that hurricanes ought to intensify, for basic thermodynamic reasons, as global warming adds more heat to the oceans. Add together this theoretical expectation with the new records today and, well, anyone would be justified in feeling pretty worried by Hurricane Dean.

Dean was also the strongest hurricane anywhere in the world so far this year -- and by far the strongest at landfall. We can only hope that somehow, the damage is lighter than expected as the storm tears across the Yucatan today and then prepares to cross the Bay of Campeche and make a second expected landfall in mainland Mexico.

For a further and more detailed discussion of Dean in its Atlantic and global context, see my "Storm Pundit" post at The Daily Green, available here.

Comments

[AndyRevkin]

Even as researchers try to clarify trends in hurricane ferocity and frequency, it's vital to remember another unassailable trend -- that ever more people, both in poor and rich countries, are getting into harm's way.

That's why scientists at all points in the hurricane-climate debate (which remains a real debate, not a manufactured one) agreed last year in a joint letter that cutting vulnerability is the top priority in hurricane zones, even as climate policy evolves.

More on that here:
http://www.nytimes.com/2006/07/25/science/earth/25coast.html
... and in Chris's book.

Andy R.

[babylonandon]

Of course more and more people are coming into harm's way!!

There ARE more and more people on this earth and a finite amount of land to put them on. Some of them choose to live where and how they shouldn't.

Some of them want to live on beaches where hurricanes come. Some of them live in flimsy structures on fault lines. Some like to live amongst the trees and scrub in areas where fires are natures' spring cleaning. Some folks love the fertile soil on the side of Mt. Vesuvius. Some folks live in mobile homes in places like Texas, Oklahoma, and Kansas and pray that the roar they hear outside is just the neighbors' truck and not a tornado.

Life is a gamble. You makes your choices and then you lives (or not!) with them.

[peterg76]

For all their drama, hurricanes are very poor indicators of the current climate changes, compared to, say, polar ice.

Of course, global warming leads to more extreme weather. Remember a really quiet hurricane season is an extreme too.

[CriminallySane]

Hurricanes are weather, polar ice is climate.

Climate changes weather. Weather reflects, imperfectly, climate.

[ReasonIsMyReligion]

I think you iced it.

[jbatch]

I think Chris missed the most important thing we can say about Dean -- that this type of extreme storm is somethig we'll see more of in the future and Climate Change is the reason we will.

So, yes, hurricanes are weather -- and polar ice melting is climate, but more extreme hurricanes are also a climatic phenomena. So, for all you deniers out there, think category 5 hitting Manhattan. It's coming. Throw in a half a foot of sea-level rise if you like for a real disaster.

Chris, stop working so hard to appear "reasonable" about climate change. People need a portrait of the possible, in all its ugly detail, not a lesson in word parsing. If you follow this issue, you know the damage that has been done by this careful prudent word parsing. Read Hansen's Scientific Reticence, if you don't know what I'm talking about.

It's time to run around with our hair on fire, bud. Past time, really.

[peterg76]

A *single* hurricane is weather. Hurricane seasons going back for decades are climate.

[klmebane]

the ice melting dilutes the oceans and lowers their salinity. salinity of water directly affects currents.

[TimmySlagle]

peterg76 writes: "a really quiet hurricane season is an extreme too."

Absolutely. So is a blooming desert, an abnormally large harvest, and a mild winter.

But when any of these things happen, nobody says anything. Because right now, the AGW talking points are FEAR. Fire, Floods, Famine, Drought, Pestilence, Plague. Everything short of a Rain of Frogs and a River of Blood.

Why is that? Why did it take a Huricane to inspire Mr. Mooney to leave this post. This is the first Hurricane in almost two years, and there is speculation that was attributed to Global Warming as well.

Everyone here seems to believe that the President is using the Fear of terrorism for nefarious purposes. Why can't anybody see that the Fear of Global Apocalypse is being used similarly?

[Skwee]

No, there have been hurricanes in the past year. Some good links I found are

http://en.wikipedia.org/wiki/2006_Atlantic_hurricane_season
http://www.msnbc.msn.com/id/12915678/

I always find it entertaining that people who claim GW is a conspiracy never say why.

[Bladernr1001]

I think the polar ice thing is being put in the spin cycle too. They show few areas where some ice has melted then tell you the whole ice cap is melting.

I looked up recent diurnal temp cycles at various spots arounf the north pole and most of the graphs never rise above the freezing mark. So I suspect the ice in those areas is not melting.

I think the globe has warmed up some. I am skeptical, however, about the cause and I am not sure about whether the magnitude of the warming is important or not. I think the whole issue is just too cloudy as to what the causes are. It is probably a combination of many causes. And it is probably the result of natual cycles too.

[baylaw73]

You may indeed be correct about the multi-causal aspect of climate change. I do think your reasearch is a bit spotty, as the noticable effect sare at the margins of the polar ice cap, and that is in theory enough to make a difference, even if the pole itself stays colder than freezing.

[TimmySlagle]

Baldernr1001 writes "I suspect the ice in those areas is not melting."

Probaby not. I tried to find out if that guy who went swimming up there last month actually found a melted hole to swim in, or it was punched open by the Russian Ice breaker that brought him there. The Director of Arctic Science at NOAA said both possibilities are equally likely.

Since the Russians dropped a couple submarines into the same hole a couple weeks later to claim the North Pole and all its resources for Mother Russia, I suspect it was punched.

[yellowdogSC]

Salt lowers the melting point of water.

Temperatures below freezing can still generate ice melt.