Hurricane Ike, which knocked Galveston and Houston with a right hook reminiscent of Katrina, again raises the question of whether global warming is fostering monster storms.
It has become almost ipso facto among many climate change scientists and activists that global warming is a key culprit behind worsening hurricanes. They point out that tropical storms feed on warmer water, and warmer sea waters are a given these days, whether you believe that the sea change is caused by Mother Nature, greenhouse gases or little green men in space.
But weather forecasters and meteorologists take a more measured view of hurricanes. Trained to distinguish between causes and consider time lines and probabilities, they do not use “weather” and “climate change” interchangeably. Weather is a sudden occurrence – albeit with a hurricane it can linger and loom with maddening deliberateness – whereas climate change is a gradual thing, building over many years.
So to the weather experts, the shorthand formula is not as simple as Storms + Warmer Waters = Worse Storms.
Given the fact of warming waters “you might expect that hurricanes would grow stronger or more numerous as the oceans warm, but there are other wrinkles. Other changes happen to earth’s atmosphere as global warming unfolds, and those may act against hurricane formation in some instances,” explained Robert Henson, a meteorologist employed as a weather writer for the University Corporation for Atmospheric Research (UCAR), a non-profit consortium of research universities based in Boulder Colorado.
The chief wrinkles:
- Pacific Ocean waters affect what happens in the Atlantic. If those waters warm faster. due to global warming, it could create winds, or wind shear, that would tend to depress hurricane formation halfway across the globe, says Henson, author of The Rough Guide to Climate Change.
- The Pacific Ocean’s regular temperature fluctuations – whether it’s an El Niño, with warmer waters in the Eastern Pacific, or La Niña year, when waters are not so warm – also plays a role in what happens on the other side of the globe. The El Niño years would tend to break up hurricane formation as their warmer winds move eastward.
- Atlantic Multi-Decadal Oscillation, an alphabet-gobbling term, that refers to the tendency of hurricanes to cycle through more active periods every thirty years or so. The National Oceanic and Atmospheric Administration (NOAA) has a chart (reprinted below) that shows how hurricanes spike in this loose pattern (loose because 125 years of records isn’t that deep for tracking patterns that span 30 years).
So how does global warming factor into this matrix of hurricane causes?
Well, warmer waters do matter. They fuel hurricanes, and contribute to large hurricanes, like Ike and Katrina, that strike, re-form, and strike again.
“All else being equal, warmer oceans can support stronger hurricanes. The extra water vapor evaporated by oceans in a warmer climate can be expected to boost rainfall from hurricanes by as much as 8% for every 1°C (1.8°F) of warming,” says NCAR scientist and global warming specialist Kevin Trenberth in an NCAR report.
Slower hurricanes, more rain-laden hurricanes, may or may not build in intensity, but do often grow larger across and pack a wider punch when they hit — although no one has yet studied this emerging trend sufficiently; so it cannot be considered verifiable, Henson said.
Are scientists pulling their punches? Not really, he says. A few years ago, meteorologists were locked in vociferous debates about whether or not the noticeable increase in Category 4 and 5 hurricanes since the mid-1990s was caused by global warming.
Today, nailing down a consensus on the degree to which global warming is creating larger storms seems to be a less urgent matter than finding ways to mitigate storm damage, Henson said.
“Hurricane experts agree. Two or three years ago they were fighting viciously about climate change. But they all agreed that we have to do a better job of protecting coastlines and building more smartly around coastlines,” Henson said.
Curbing greenhouse emissions to slow climate change is just one-side of the answer, adapting to the changes that are already here and likely cannot be reversed for decades, is as critical, he said.
In an analysis “Confronting Climate Change in the Gulf Coast,” the UCS authors note that “…vital but difficult-to-predict climate-driven changes include potential shifts in El Niño/La Niña cycles, hurricanes, storms, and coastal ocean currents.”
The kicker: “Even if storm intensities remain constant, however, disturbance from coastal flooding and erosion will increase because rising sea levels will generate higher storm surges even from minor storms.”
The report was written well before Ike crashed into Texas and Louisiana causing billions in property damage and claiming more than 40 lives across the U.S. before expiring many states northward. (The picture left is a before and after photo by the US Geological Survey of Ike’s devastation of Bolivar Peninsula near Galveston.)
IKE of course was more than a “minor” storm, but the power of its water surge was what left a mark across a wide swath of coast, creating havoc that belied its Category 3 rating (a ranking based on top wind speeds within the storm).
As it turns out, IKE charted higher on a different scale: The storm, reminiscent of the one that destroyed Galveston a century ago, rated very high, nearly as high as they go, on the newly proposed (by NOAA scientists) Integrated Kinetic Energy scale that looks at the winds, waves and surge potential of a storm.
Yup, the acronym for that would be IKE.
Hurricanes/Tropical Storm Frequency (1885-2005)
Red – Category 3 and greater
Green – Hurricanes
Yellow – Named Systems
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