Planting Trees to Fight Warming Brings New Woes

Some scientists advocate growing trees to absorb carbon — the biggest contributor to climate warming — out of the air. But scientists have discovered that large-scale tree growing brings its own problems and worry that the solution may substitute one environmental disaster for another.

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MICHELE NORRIS, host:

Rarely a week goes by without some new scientific study of climate change. This week, there were troubling reports on the speed of warming. Scientists studying the frozen soil of the arctic, the permafrost, say it's melting at an alarming rate.

ROBERT SIEGEL, host:

Another study indicates that reducing some pollution might actually make the Earth warmer. It shows certain pollutants float high up into the atmosphere, scattering and absorbing more sunlight than once thought. In effect, this haze of pollutants acts like sunblock and keeps the Earth a little cooler than it would otherwise be. However, as factories and cars get cleaner, there will be less of that industrial sunblock, and the Earth could get warmer faster.

NORRIS: News like this tends to spur efforts to reduce the industrial gases that worsen the warming, especially carbon dioxide, the main greenhouse gas. One solution is tree planting. As grade-school textbooks will tell you, plants absorb carbon dioxide and use it to grow. But now there's another new study that warns that trees are no panacea. NPR's Christopher Joyce reports.

CHRISTOPHER JOYCE reporting:

Plant trees, save the planet. What's not to like about that? Many climate scientists and environmentalists view tree planting as having their climate cake and eating it, too. Trees help stop erosion, they provide homes for animals, they're nice to look at and maybe they can save us from ourselves by sucking down carbon dioxide from our smokestacks and tailpipes. But that's asking trees to do a lot.

Mr. ROBERT JACKSON (Duke University): These are huge numbers of fossil fuel emissions, the carbon dioxide that goes to the atmosphere.

JOYCE: That's ecologist Robert Jackson from Duke University.

Mr. JACKSON: So it has to be millions of acres of trees or it's not even worth talking about. And when you get to that scale of land management, you have to ask: `What else will happen?'

JOYCE: So Jackson asked. He looked into what happens to soil and water around large tree plantations. He traveled a lot and made his own measurements, as well. Here's what he found.

Mr. JACKSON: Within a decade, plantations reduced stream flow by about one half compared to shrublands or grasslands they replaced, and about one out of every eight streams dried up completely for a full year or more.

JOYCE: Besides using up a lot of water, plantations sometimes consume all the nutrients in poor soils and leave them salty and acidic. Jackson's research paper in the journal Science is drawing attention from ecologists such as Peter Frumhoff with the Union of Concerned Scientists.

Mr. PETER FRUMHOFF (Union of Concerned Scientists): The paper's an enormously important cautionary tale, that we can't look solely through the lens of climate and carbon in thinking about the role of trees as a climate mitigation strategy.

JOYCE: Frumhoff notes that seven Northeastern states have just agreed to a plan to make industry reduce carbon dioxide emissions in the US, and it includes planting trees. If, say, a power company has to cut 200 tons of CO2 emissions a year, it could do that by collecting it at the smokestack or by planting 150 acres of pine trees. Frumhoff and Jackson support the idea of tree planting to offset carbon emissions, but they say plantations need careful planning to avoid environmental damage. And in the rush to fight climate change, that might not always happen.

Mr. FRUMHOFF: The concern is that as you move internationally, there's less oversight, less capacity to ensure that not only there's environmental benefits on the ground, but indeed that the climate benefits are realized, as well.

JOYCE: Tree planting is also a big part of the climate plan under the international Kyoto Treaty. The treaty gives less-developed countries, many with large tropical forests, incentives to keep their forests intact or to plant new ones. That's fine, says Duke's Robert Jackson, but it's a temporary strategy.

Mr. JACKSON: What we're doing primarily with plantations is trying to buy time, trying to buy a few decades here and there to give companies and individuals the opportunity to transform technologies so that a power company doesn't have to build a brand-new plant today.

JOYCE: Ultimately, Jackson says, the biggest reductions will have to come from cutting carbon dioxide at the source: power plants, cars and forests that release CO2 when they're burned or cut down. Christopher Joyce, NPR News.

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