Can carbon offsets cut pollution?

Despite the best intentions of brides and grooms, guests add to pollution just by getting to the wedding. So what do you do? Some couples buy carbon offsets.

Here's how they work. First, calculate how much carbon -- pollution -- you produce. About 90% is generated by travel, says Eric Carlson of Carbonfund.org, a non-profit carbon exchange program. Its website has several carbon- offset calculators, including one for weddings.

Then the calculator gives you a price based on the number of pounds of carbon you produce.

The companies spend a portion of the money sent in to "offset" your pollution by investing in projects such as solar and wind power, supporting reforestation or buying offsets from the Chicago Climate Exchange, where companies buy and sell rights to produce carbon emissions.

"Carbon offsets are already reducing carbon dioxide emissions, increasing investment in clean technology and driving the price of renewable energy down," Carlson says.

Some critics argue that carbon offsets simply don't work.

"Once emissions come out of your car or out of a plane, they are causing environmental damage, and they don't disappear, no matter how much money you wave at them," Kevin Smith, a London-based researcher at the Carbon Trade Watch group, says in an e-mail.

Carbon offsets can help reduce pollution if done properly, says a 2006 report by the Tufts Climate Initiative at Tufts University.

But voluntary programs won't solve global warming, the report says. "No voluntary approach ... should be allowed to delay or replace a mandatory federal cap on carbon emissions or a worldwide tax on jet fuel."