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Resting On (Mountain) Laurels

Trees won’t absorb all of our carbon dioxide. What will?

By Matthew S. Meisel

As the hippie days of the 1960s drew to a close, the British scientist James Lovelock began to formulate a fittingly hippie (yet still innovative) theory about the earth. He believed that the living and non-living parts of the earth form a single, self-regulating system. When some change occurs within the “system,” some other part of the system reacts to restore the original conditions. He called the theory the Gaia hypothesis, after Gaia, the Greek goddess of earth.

The theory helps to explain some interesting things about the history of earth’s atmosphere. But the most optimistic element of the Gaia hypothesis is its forward-looking aspect. Taken to its extreme, the theory suggests that global warming will fix itself, at least partially. But there is increasing evidence that the most optimistic element of the Gaia hypothesis is, unfortunately, false.

There is certainly some scientific truth to the hypothesis: The Earth does have some self-regulating properties. But is that the case for atmosphere-warming carbon dioxide? If the earth is self-regulating, the theory goes, then an increase in atmospheric carbon dioxide should mean an increase in plant growth. Plants, after all, scrub carbon dioxide from the atmosphere, so more plants should mean less carbon dioxide—thus countering the initial increase.

As it turns out, the situation is far more complex. In a paper published in next Tuesday’s Proceedings of the National Academy of the Sciences, a team of climate researchers reports that worldwide tree growth would actually warm the atmosphere, despite the corresponding decrease in atmospheric carbon dioxide.

The main reason has to do with the Arctic and Antarctic. As polar climates warm enough for trees to move in, the color of that part of the earth will change, as viewed from above. Green trees, which absorb more light, will replace whiter snow and ice, which reflect more rays back to space. Like a dark-colored car hood on a hot day, a dark-colored earth will warm. The group’s computer modeling experiments show that the localized warming due to the change in the earth’s surface reflectivity (called its “albedo”) would be greater than the global cooling due to the carbon dioxide the trees absorb.

The situation is a little different in the tropical regions. Tropical soils are much darker than polar snows, so replacing open land with trees makes little difference as to how much light the land reflects. In fact, planting trees in the tropics actually cools the earth. Warm-weather trees help to draw water out of the ground and into the atmosphere, creating clouds that reflect light and keep the atmosphere cool.

So while it is important to protect our tropical forests, turning Greenland into one big woodland is a decidedly bad idea. “Large-scale afforestation”—that is, tree growth—“implemented in temperate latitudes may be largely ineffectual in mitigating global warming,” the authors write.

The immediate lesson is not to take a chainsaw to all of Alaska. “Clear-cutting mountains to slow climate change is, of course, nuts,” wrote Ken Caldeira, a scientist at the Carnegie Institution and one of the study’s authors, in a January op-ed in The New York Times. Slowing global warming while destroying ecosystems is poor policy, he says. But so is blindly planting trees.

There’s a larger lesson here, however, than where not to plant trees: Optimism alone will not slow climate change. The Gaia hypothesis, taken to an extreme, implies that humans can sit back and watch the Earth warm, and eventually the earth will respond and restore itself. The view is characteristic of many individuals’ (and nations’) attitudes today. True, the earth will respond, but when it’s finished responding, it won’t look anything like the earth we have now. By now, you’ve probably heard the litany of changes, which was repeated in stark terms in last Friday’s report of the Intergovernmental Panel on Climate Change (IPCC): higher sea levels, more extreme weather events, decreased agricultural production in many regions, severely threatened ecosystems, and mass extinctions of hundreds of thousands of species.

There is reason to be optimistic. Government regulations—unlike new Arctic forests—on carbon emissions would curb global warming. Restrictions on carbon dioxide pollution would, in turn, spur technological innovation and reward those who use energy more efficiently and help others to as well. The IPCC estimates that if we don’t address climate change, we’ll see worldwide losses of one percent to five percent GDP by the end of the century. Even modest economic investment now in cleaner technologies will yield enormous benefits for our children’s and grandchildren’s generations.

In the meantime, we must stop pretending climate change doesn’t exist. And we can’t rely on the environment to do the tough work for us.

Matthew S. Meisel ’07 is a chemistry concentrator in Currier House. His column appears on alternate Fridays.

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