Loop Guru (The Hidden Kristof)

Nicholas Kristof takes on global warming in his Sunday column, Warm, Warmer, Warmest (full column available to Times Select subscribers), beginnign with what he sees as the most dangerous aspect of global warming--positive feedback loops. Huh?

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.

[...]

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.

Politically, though, we're stuck in a rut:

"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."

I've got more on permafrost on the flip...


: : : : : : : : : :

Last spring, the New Yorker had three extraordinary articles on The Climate of Man by Elizabeth Kolbert, which are unfortunately no longer available online at the New Yorker site (luckily, I grabbed PDFs of them). Here's a bit on permafrost from her first part of the tryptich (from the April 25, 2005 New Yorker issue):

When you walk around in the Arctic, you are stepping not on permafrost but on something called the “active layer.” The active layer, which can be anywhere from a few inches to a few feet deep, freezes in the winter but thaws over the summer, and it is what supports the growth of plants—large spruce trees in places where conditions are favorable enough and, where they aren’t, shrubs and, finally, just lichen. Life in the active layer proceeds much as it does in more temperate regions, with one critical difference. Temperatures are so low that when trees and grasses die they do not fully decompose. New plants grow out of the half-rotted old ones, and when these plants die the same thing happens all over again. Eventually, through a process known as cryoturbation, organic matter is pushed down beneath the active layer into the permafrost, where it can sit for thousands of years in a botanical version of suspended animation. (In Fairbanks, grass that is still green has been found in permafrost dating back to the middle of the last ice age.) In this way, much like a peat bog or, for that matter, a coal deposit, permafrost acts as a storage unit for accumulated carbon.

One of the risks of rising temperatures is that this storage process can start to run in reverse. Under the right conditions, organic material that has been frozen for millennia will break down, giving off carbon dioxide or methane, which is an even more powerful greenhouse gas. In parts of the Arctic, this is already happening. Researchers in Sweden, for example, have been measuring the methane output of a bog known as the Stordalen mire, near the town of Abisko, for almost thirty-five years. As the permafrost in the area has warmed, methane releases have increased, in some spots by up to sixty per cent. Thawing permafrost could make the active layer more hospitable to plants, which are a sink for carbon. Even this, though, probably wouldn’t offset the release of greenhouse gases. No one knows exactly how much carbon is stored in the world’s permafrost, but estimates run as high as four hundred and fifty billion metric tons.

[...]

For the same reason that it is sweaty in a coal mine --heat flux from the center of the earth--permafrost gets warmer the farther down you go. Under equilibrium conditions--which is to say, when the climate is stable--the very warmest temperatures in a borehole will be found at the bottom and they will decrease steadily as you go higher. In these circumstances, the lowest temperature will be found at the permafrost’s surface, so that, plotted on a graph, the results will be a tilted line. In recent decades, though, the temperature profile of Alaska’s permafrost has drooped. Now, instead of a straight line, what you get is shaped more like a sickle. The permafrost is still warmest at the very bottom, but instead of being coldest at the top it is coldest somewhere in the middle, and warmer again toward the surface. This is an unambiguous sign that the climate is heating up.