Let's go back to those Iowa floods. Humans surely contributed to the calamity: Farmland in the Midwest has been plumbed with drainage pipes; streams have been straightened; most of the state's wetlands have been engineered out of existence; land set aside for conservation is being put back into corn production to meet the demands of the ethanol boom. This is a landscape that's practically begging to have 500-year floods every decade.

Was climate change a factor in the floods? Maybe. A recent report from the National Oceanic and Atmospheric Administration said that heavier downpours are more likely in a warming world. Thomas Karl, a NOAA scientist, says that there has been a measurable increase in water vapor over parts of the United States and more precipitation in the Midwest.

But tree-ring data indicate that the state has gone through a cycle of increasing and decreasing rainfall for hundreds of years. The downpours this year weren't that unusual, according to Harry J. Hillaker Jr., the Iowa state meteorologist. "The intensity has not really been excessive on a short-term scale," he said. "We're not seeing three-inch-an-hour rainfall amounts."

This will be a wet year (as was last year), but Iowa may not set a rainfall record. The wettest year on record was 1993. The second wettest: 1881. The third wettest: 1902.

Iowa is an awkward place to talk about global warming, because the state has actually been a bit cooler in the summer than it was in the first half of the 20th century. Hillaker says the widespread shift to annual plants (corn and soybeans) and away from perennial grasses has altered the climate. The 10 hottest summers in Iowa have been, in order, 1936, 1934, 1901, 1988, 1983, 1931, 1921, 1955, 1933 and 1913. Talk about extreme weather: One day in 1936, Iowa set a state record with a high temperature of 117 degrees. And no one blamed it on global warming.

Rest assured, we may find ways to ruin the planet even before the worst effects of global warming kick in. The thing that gets you in the end is rarely the thing you're paying attention to.

The basic problem is that there are so many of us now. Four centuries ago, there were about 500 million people on Earth. Today there are that many, plus 6 billion. We're rapidly heading toward 9 billion. Conservatives say that we just need to focus on maintaining free markets and let everything sort itself out through the miracle of the invisible hand. But the political tide is turning against unfettered free markets and toward greater regulation. Climate-change policy is part of that: Somehow we've got to embed environmental effects into the cost of energy sources, consumer goods and so on. The market approach by itself has let us down.

Viewed broadly, it appears that humans are environment-destroying creatures by nature. The notion of the prelapsarian era in which we lived in perfect harmony with nature has been effectively shattered by such scientists as Jared Diamond, the author of "Collapse," and Tim Flannery, who wrote "The Future Eaters." If everything gets simplified and reduced to a global-warming narrative, we'll be unable to see the trees for the forest.

Consider the June issue of Scientific American, where you'll find a photograph of a parched lake, the mud baked into the kind of desiccated tiles that scream "drought." The caption says: "Climate shift to unprecedentedly dry weather, along with diversion of water for irrigation, has converted this former reservoir in China's Minqin County into desert."

Um . . . "this former reservoir?" Look closely, and you can see concrete walls in the background. This is not a natural place: It's a manufactured landscape. Here's a wild guess: This part of China is an environmental disaster that has very little to do with climate change and very much to do with high population and intensifying agriculture.

Last week, we saw reports of more wildfires in California. Sure as night follows day, people will lay some of the blame on climate change. But there's also the minor matter of people building homes in wildfire-susceptible forests, overgrown with vegetation due to decades of fire suppression. That's like pitching a tent on the railroad tracks.

The message that needs to be communicated to these people is: "Your problem is not global warming. Your problem is that you're nuts."

You should definitely worry about global warming. But you don't need to worry about global warming when your house is on fire.

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