By NICHOLAS D. KRISTOF
One of the hottest environmental battles has been over oil drilling in the coastal plain of the Arctic National Wildlife Refuge, but the sad reality is that much of the Arctic plain will probably be lost anyway in this century to rising sea levels.
That should be our paramount struggle: to stop global warming. It threatens not only the Arctic plain, but also low-lying areas around the world with 100 million inhabitants. And it could be accelerating because of the three scariest words in climate science: positive feedback loops.
Bear with me now: a positive feedback loop occurs when a small change leads to an even larger change of the same type. For example, a modest amount of warming melts ice in northern climates. But the bare ground absorbs three times as much heat as ground covered by snow or ice, so the change amplifies the original warming. Even more ice melts, more heat is absorbed, and the spiral grows.
That feedback loop is well understood and part of climate models, but others aren't.
For example, perhaps the biggest single source of uncertainty about whether Lower Manhattan will be underwater in 2100 has to do with the glaciers of Greenland. If Greenland's ice sheet melted completely, that alone — over centuries — would raise the oceans by 23 feet. And those glaciers are dumping much more water into the oceans than they did a decade ago, according to two satellite surveys just published, but the studies disagree on the amounts.
Positive feedback seems to be at work. As a glacier melts a little, the water trickles down to the rock and lubricates the glacier's slide toward the sea. So, because of this and other effects, some of Greenland's glaciers are now, in glacial terms, rocketing toward the sea at 7.5 miles a year.
Here's another positive loop. The Arctic permafrost may hold 14 percent of the world's carbon, but as it melts, some of its carbon dioxide and methane are released, adding to the amount of greenhouse gases. So more permafrost melts.
Likewise, millions of years ago, warming oceans with vast amounts of methane in their depths had great episodes of methane belching, which added to the greenhouse effect then. I don't expect the oceans to burp in the same massive way tomorrow, but if they did, no one would know how to fit those unmannerly oceans into a climate model.
Part of the challenge in modeling climate is that we're already off the charts with greenhouse gases like nitrous oxide, carbon dioxide and methane. "We've driven them out of the range that has existed for the last one million years," noted James Hansen, NASA's top climate expert. "And the climate has not fully responded to changes that have already occurred."
In fairness, there are also negative feedback loops, which could dampen change. For example, warmer temperatures could mean more snow over Antarctica, implying an initial buildup of the Antarctic ice sheet. The added ice could slow global warming and rising sea levels. But a new study just published in Science Express says that the Antarctic ice sheet is already thinning significantly — raising more alarms and casting doubt on that negative feedback.
In any case, it's clear that negative feedback loops in climatology are much less common than positive loops, which amplify change and leave our climate both unstable and vulnerable to human folly.
Still with me?
Look, I know that climate science can be — here's a shock — boring! But it's better for us to slog through it now than for coming generations to slog through the rising waters of, say, Manhattan. It may be more exciting to thump the table about Iraq or torture — or even the preservation of the Arctic National Wildlife Refuge — and those are all hugely important. But global warming may ultimately be the greatest test we face as stewards of our planet. And so far we're failing catastrophically.
"Historians of science will be brutal on us," said Jerry Mahlman, a climate expert at the National Center for Atmospheric Research. "We are right now in a state of deep denial about how severe the problem is. Political people are saying, 'Well, it's not on my watch.' They're ducking for cover, because who's going to tell the American people?"
We know what to do: energy conservation, gas taxes and carbon taxes, more renewable energy sources like wind and solar power, and new (and safe) nuclear power plants. But our political system is paralyzed in the face of what may be the single biggest challenge to our planet.
"Are we an intelligent species or not?" Dr. Mahlman asked. "Right now, the evidence is against it."
