Can planting a tree make an SUV okay? It's not that simple

Published May 28, 2007

ALBANY, N.Y. - If you plant some trees, is it okay to drive an SUV?

The question isn't as silly as it sounds. People worried about global warming increasingly are trying to "offset" the carbon dioxide - the leading greenhouse gas - they spew into the atmosphere when they drive, fly or flick on a light. One idea popular with the eco-conscious is to have trees planted for them. You get to keep driving and flying, but those trees are supposed to suck in your trail of carbon.

But some researchers say planting trees - while a good thing - is at best a marginal solution to global warming.

To those critics, plantings and other carbon offsets are like the medieval practice of selling indulgences to wash away sins: It may feel good, but it doesn't solve much.

"The sale of offset indulgences is a dead-end detour off the path of action required in the face of climate change, " says a report by the Transnational Institute's Carbon Trade Watch.

Groups that offer tree offsets typically rely on Web calculators requiring users to type in how many miles they drive, how much electricity they use and how far they fly. Figure out how much CO2 someone is responsible for (output), compare it to the work average trees can do (input), and you have a formula for neutralizing a person's "carbon footprint."

For $40, Trees for the Future will plant 400 trees in a developing country to handle your car emissions. In June, Delta Air Lines will allow online ticket buyers to help offset emissions of their flights through tree plantings in the United States and abroad: $5.50 for domestic round trips, $11 for international.

"It's easy to do and it makes a big difference, " said Jena Thompson of the Conservation Fund.

The science is sound: Trees take in carbon dioxide as part of photosynthesis and store the carbon. But even conservationists caution it's not as simple as planting a sapling so you can crank up the air conditioning without guilt.

Offset groups use averages to estimate how much carbon a given tree or forested acre can capture. For instance, the nonprofit Conservation Fund figures that each tree planted captures less than 1 1/2 tons over 100 years.

To put that in perspective, consider that about 7.3-billion metric tons of carbon dioxide was produced from the burning of fossil fuels worldwide in 2003, the most recent estimate available.

And how much carbon dioxide a tree can soak up varies, said John Kadyszewski of Winrock International, a nonprofit that works on environmental projects. A huge California redwood might have 30 tons of carbon stored while a 100-year-old pine might have less than a ton.

Kadyszewski notes that most of the calculators use conservative numbers, meaning they're not likely to exaggerate benefits. The Conservation Fund and Carbonfund.org both say they plant more than enough trees to deliver on promised offsets.

However, some researchers say it's simply not possible to plant enough trees to have a significant effect on global warming.

Michael MacCracken, chief scientist at the nonpartisan Climate Institute in Washington, said tree-planting has value as a stopgap measure while society attempts to reduce greenhouse gases. But University of Victoria climate scientist Andrew Weaver fears tree offsets could steal the focus of a problem that requires technological advances and behavioral changes.

"The danger is that you could actually think you're solving a problem, " Weaver said. "It makes you feel good. It makes you feel warm and fuzzy, like changing a couple of light bulbs. But the reality is it's not going to have a significant effect."

Eric Carlson of the tree-planting nonprofit Carbonfund.org notes that his group does not promote trees as the only solution to climate change.

"You can find pluses and minuses to all the offset options, " Carlson said, "but the worst thing is to do nothing."