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Finding the Fingerprints of Climate Change in Storm Damage -- a Very Long Detective Story

By Evan Lehmann
The New York Times
Some U.S. insurers have expanded their focus to look at the warming impacts on things like flooding, ice storms and nor'easters, said Sharlene Leurig, senior manager of the insurance program at Ceres, an organization for institutional investors concerned about climate change.

Hurricanes could become more prevalent with climate change, but the economic pain they deliver might not be recognized as man-made for 260 years.

That means smashed homes and ruined roads may not be attributable to greenhouse gases for centuries, according to new research that suggests climate policies like adaptation should be designed without financial evidence of climate-enhanced windstorms.

The researchers also warn environmentalists and policymakers against making claims that damage from Hurricane Katrina and other storms are rising from carbon dioxide emissions. Insurance companies that promote climate change as a reason for rising prices could also lose credibility.

The researchers "urge extreme caution in attributing short term trends (i.e., over many decades and longer) in normalized US tropical cyclone losses to anthropogenic climate change."

"Not only is short term variability not 'climate change' (which the IPCC defines on time scales of 30 to 50 years or longer), but anthropogenic climate change signals are very unlikely to emerge in US tropical cyclone losses at time scales of less than a century under the projections examined here," says the analysis accepted by the journal Environmental Research Letters.

Economic losses are seen as a potent storyteller about climate change. If greenhouse gases could be shown to increase financial damages, that might accelerate efforts to develop stronger buildings codes, influence insurance prices for coastal homes, and discourage development in risk-prone areas.

But the research tells a different story, at least for hurricanes. As a backdrop, it uses a landmark study published in Science last January finding that the number of strongest hurricanes, categories 4 and 5, could double in 100 years because of climate change.

The researchers begin by assuming that's true. Then they apply hurricane damage data from the past century to those future hazards, adjusting for growth in population, inflation and wealth.

Finding the signals in weather cycles

The results indicate that future hurricane damages won't produce a tangible "climate signal" for at least 120 years, and perhaps not for 550 years. The average time before a signal might be seen is 260 years, according to the combined findings of an 18-model ensemble used by the researchers. In that year, 2271, climate change is expected to increase damage by 106 percent, more than double.

The researchers know this is a touchy topic. It could be perceived as an effort to downplay the impacts of climate change, or be seen with alarm by environmentalists advocating for action now to cut carbon pollution.

"It's not to dispute that [global warming] is happening or what influence it will have on hurricanes," said Ryan Crompton, a co-author and a catastrophe risk expert with Risk Frontiers, a research organization at Macquarie University near Sydney, Australia, that is funded in part by the insurance industry.

"It's not like in years 1 through 259 there's no change on average in the damage," he added. "Then, all of sudden, it gets to year 260 and it increases by 106 [percent]. That 260 years ... is how long before we can say in terms of detection and attribution, 'Yes, there's the [climate] signal.'"

Parsing damages from hurricanes attributable only to greenhouse gases is a difficult process. So far, it hasn't been done with conviction. Still, a month ago, researchers at the London School of Economics released an unpublished paper indicating that the United States has seen a 5 percent rise in climate hurricane damages since 1973. They cautioned, however, that the findings were tentative and may have been influenced by variables other than global warming (ClimateWire, Nov. 29, 2010.).

Atlantic's fiercest storms may double

The signature of a warming Earth will reveal itself in the number of hurricanes before it's seen in the damages the storms inflict. The study released last year in Science estimates that the number of severe storms with wind speeds reaching at least 131 miles per hour will rise 10 percent each decade. On that pace, the frequency of the Atlantic's fiercest storms would double by 2110. Weaker storms, meanwhile, would abate.

So why wouldn't climate-related damage rise at the same rate as hurricane frequency? Because buildings and infrastructure are not located uniformly along the country's coastlines, and some are constructed more robustly than others. A climate-influenced storm, in other words, could rip ashore in an unpopulated area of Florida and do little damage. That dilutes the climate signal in economic losses.

In that way, the economic loss research confirms what Tom Knutson, a research meteorologist with the National Oceanic and Atmospheric Administration and an expert on climate change and hurricanes, has considered common sense: Climate change will reveal itself first in the hazard, then in the damage.

"Nothing too earth-shattering here," Knutson said. "This study actually doesn't tell me much that I already sort of have a notion of anyway. Namely, that if one is looking for a signal of climate change in the hurricane record, damage is not the first place to go to look for it."

But Roger Pielke Jr., a professor of environmental studies at the University of Colorado, Boulder, and co-author of the new economic loss research, says the findings are evidence that policymakers will have to grapple in the dark with global warming. If they wait for economic proof before addressing climate change, valuable options around adapting to storms will slip their grip.

A tool to restrict insurance premiums?

He also has a warning for insurers and catastrophe modelers: Don't overplay current climate risks.

"If you have a vested interest in particular outcomes, you want to try to emphasize that science or that information that best makes your case," Pielke said of Munich Reinsurance and other companies that emphasize addressing climate change. "If there's an expectation that losses over the next few years are going to be higher because of climate change, it provides a scientific, quote-unquote, basis for justifying rate increases."

"Because your credibility is hard to gain and easy to lose in the area, and they don't want to be seen as going beyond what the science can support," he cautioned.

Others are viewing the climate risks through a different lens. Some U.S. insurers have expanded their focus to look at the warming impacts on things like flooding, ice storms and nor'easters, said Sharlene Leurig, senior manager of the insurance program at Ceres, an organization for institutional investors concerned about climate change.

"I think a number of the largest players in the industry are realizing it's not just hurricanes and that it's not just a future trend," she said of global warming. "It's very much something that's affecting statistics today."

Among those are floods that insurers and the U.S. Federal Emergency Management Agency once considered a risk that would come once in 100 years. Some areas have seen repetitive flooding on a much shorter timeline.

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