Carbon offsets: they're not just for celebrities anymore.

Al Gore claims to offset the pollution caused by his jet-setting from lecture to lecture on his An Inconvenient Truth tour by purchasing carbon offsets. In effect, he funds activities that will remove as much carbon dioxide from the air as his heavy travel schedule puts into it.

Online ticketing agency Travelocity is now extending the option of purchasing carbon offsets to ordinary people.

Customers who book vacations packaged through the site have the option of purchasing a tax-deductible carbon offset at checkout: The company suggests a $10 donation to mitigate round-trip air travel, a one-night hotel stay, and car rental for one person; $25 for a longer trip for two people; and $45 for a party of four.