Perfect storm

Did global warming cause Hurricane Katrina?

It’s impossible to say. The earth’s weather system is so complex that no single event, such as a Category 5 hurricane, can be said to have a single cause.

It is possible, however, to recognize trends in the weather, and one of those trends is toward stronger hurricanes, a change correlated with increases in global temperatures and in the temperatures of ocean waters. Scientists are now predicting that, as global temperatures continue to increase, so will the force of hurricanes.

In that sense, Katrina was a preview of what’s coming: more and more devastating hurricanes hitting this country and others. It was a preview in another way, as well. New Orleans is the only major city in America that is below sea level. Scientists are now predicting that if global warming continues at its current rate, sea levels will rise by anywhere from three to 20 feet by the end of this century, meaning many coastal cities will be as vulnerable as New Orleans was. Hundreds of thousands of people became homeless in New Orleans; in Calcutta, the number would be in the millions.

Travelers to the planet’s icy regions all report that the polar ice caps are melting. Photos from space dramatically show how large the ice caps once were and how much they’ve shrunk in a short time. Glaciers everywhere are receding at unprecedented speed. In the past year, scientists have begun to realize that, as Time magazine reported earlier this month, the earth has reached a “tipping point.” Forget about slow but gradual warming; think sudden collapse.

Why? Because global warming, scientists now know, is a self-accelerating process fed by feedback loops. “Climate disruptions feed off one another in accelerating spirals of destruction,” as Time puts it. Consider the polar ice caps. Ice reflects as much as 90 percent of the sunlight that hits it, sending much of its energy back into space. Water, on the other hand, absorbs 90 percent of the sun’s energy it receives. As the ice caps melt and the water surrounding them warms up, the ice melts ever faster.

These kinds of changes and many others are affecting the oceans’ temperatures and currents. To stronger hurricanes add the increased frequency of El Niño and La Niña patterns; horrific droughts and resulting wildfires in some areas; animal species being pushed to the edge of extinction; and possible disruption of the Gulf Stream, whose tropical waters keep Europe, which is at the same latitude as Alaska, relatively warm.

Two years ago, when Stanford University professor Stephen Schneider, an expert on global warming, visited Chico, he asked a simple question: “If there’s a 1 percent chance the wing on a plane is going to fall off, are you going to get on it?”

His point was that, while it was still conceivable that global warming might turn out to be merely a fluctuation in planetary temperature cycles, as some would like to believe, there was also a very real possibility that it was a new and extremely dangerous trend. What mattered, Schneider said, is how we responded: Did we ignore the possibility, even if it was only 1 percent, or did we deal with it?

Two years later, it’s become clear that, whatever the risk from global warming, it’s far greater than 1 percent. In fact, for all practical purposes, the debate over global warming is over. Global warming is happening and can’t be avoided. We have to get used to it, and we absolutely must act to turn the process around.

As Al Gore puts it, we need the equivalent of a Marshall Plan for the earth’s climate. Global warming is the greatest challenge human beings have ever faced. It’s a crisis, Gore says, but it’s also an opportunity for the people of the world to work together in common purpose. On Earth Day this Saturday, that’s something to think about.