Global Warming Did It! Well, Maybe Not.

By Joel Achenbach
Sunday, August 3, 2008

We're heading into the heart of hurricane season, and any day now, a storm will barrel toward the United States, inspiring all the TV weather reporters to find a beach where they can lash themselves to a palm tree. We can be certain of two things: First, we'll be told that the wind is blowing very hard and the surf is up. Second, some expert will tell us that this storm might be a harbinger of global warming.

Somewhere along the line, global warming became the explanation for everything. Right-thinking people are not supposed to discuss any meteorological or geophysical event -- a hurricane, a wildfire, a heat wave, a drought, a flood, a blizzard, a tornado, a lightning strike, an unfamiliar breeze, a strange tingling on the neck -- without immediately invoking the climate crisis. It causes earthquakes, plagues and backyard gardening disappointments. Weird fungus on your tomato plants? Classic sign of global warming.

You are permitted to note, as a parenthetical, that no single weather calamity can be ascribed with absolute certainty (roll your eyes here to signal the exasperating fussiness of scientists) to what humans are doing to the atmosphere. But your tone will make it clear that this is just legalese, like the fine-print warnings on the flip side of a Lipitor ad.

Some people are impatient with even a token amount of equivocation. A science writer for Newsweek recently flat-out declared that this year's floods in the Midwest were the result of climate change, and in the process, she derided the wishy-washy climatologists who couldn't quite bring themselves to reach that conclusion (they "trip over themselves to absolve global warming").

Well, gosh, I dunno. Equivocation isn't a sign of cognitive weakness. Uncertainty is intrinsic to the scientific process, and sometimes you have to have the courage to stand up and say, "Maybe."

Seems to me that it's inherently impossible to prove a causal connection between climate and weather -- they're just two different things. Moreover, the evidence for man-made climate change is solid enough that it doesn't need to be bolstered by iffy claims. Rigorous science is the best weapon for persuading the public that this is a real problem that requires bold action. "Weather alarmism" gives ammunition to global-warming deniers. They're happy to fight on that turf, since they can say that a year with relatively few hurricanes (or a cold snap when you don't expect it) proves that global warming is a myth. As science writer John Tierney put it in the New York Times earlier this year, weather alarmism "leaves climate politics at the mercy of the weather."

There's an ancillary issue here: Global warming threatens to suck all the oxygen out of any discussion of the environment. We wind up giving too little attention to habitat destruction, overfishing, invasive species tagging along with global trade and so on. You don't need a climate model to detect that big oil spill in the Mississippi. That "dead zone" in the Gulf of Mexico -- an oxygen-starved region the size of Massachusetts -- isn't caused by global warming, but by all that fertilizer spread on Midwest cornfields.

Some folks may actually get the notion that the planet will be safe if we all just start driving Priuses. But even if we cured ourselves of our addiction to fossil fuels and stabilized the planet's climate, we'd still have an environmental crisis on our hands. Our fundamental problem is that -- now it's my chance to sound hysterical -- humans are a species out of control. We've been hellbent on wrecking our environment pretty much since the day we figured out how to make fire.

T his caused that: It would be nice if climate and weather were that simple.

But "one can only speak rationally about odds," Kerry Emanuel, a climatologist at the Massachusetts Institute of Technology who has studied hurricanes and climate change, told me last week. "Global warming increases the probabilities of floods and strong hurricanes, and that is all that you can say."

Emanuel's research shows that in the past 25 years, there's been an uptick in the number of strong storms, though not necessarily in the number of hurricanes overall. Climate models show that a 1-degree Celsius rise in sea-surface temperatures should intensify top winds by about 5 percent, which corresponds to a 15 percent increase in destructive power. The tropical Atlantic sea surface has warmed by 0.6 degrees Celsius in the past half-century.

At my request, Emanuel ran a computer program to see how much extra energy Hurricane Katrina had because of increases in sea-surface temperature. His conclusion: Katrina's winds were about 2 percent stronger in the Gulf, and not significantly stronger at landfall. Maybe climate change was a factor in generating such a storm, or in the amount of moisture it carried, but the catastrophe that Katrina caused in New Orleans can more plausibly be attributed to civil engineers who built inadequate levees, city planning that let neighborhoods materialize below sea level and Bush administration officials who didn't do such a heckuva job.

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