While celebrities like Al Gore and Gov. Arnold Schwarzenegger burnish their green credentials by buying so-called carbon offsets that fund projects like wind farms to make up for their energy excesses, environmental advocates nationwide criticize the effectiveness of the programs.

Their concern: The carbon offset market, which is largely unregulated, lacks the standards or the oversight needed to make sure that the projects consumers send money to are actually helping clean the air.

Since 2002 the number of organizations selling carbon credits has grown by 200 percent, with online retailers expanding even faster, according to a report released last month by research firm EcoSystem Marketplace.

Popular online travel sites like Travelocity and Expedia let customers offset carbon emissions from air travel by paying extra for a ticket. Last year, Gore's "Inconvenient Truth" struck a nerve with audiences, raising interest in fighting global warming. And big companies like Google have announced plans to become "carbon neutral" and buy offsets.

Get the full story at the San Jose Mercury News