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KAI RYSSDAL: There was some unintended corporate irony from BP today. The oil giant launched a new website. It'll let drivers offset their tailpipe emissions. Balance out their pollution. Every little bit helps in the fight against global warming. But who gets helped the most? From the Marketplace Sustainability Desk, Sam Eaton took a peek under the hood of today's announcement.

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SAM EATON: BP's new website is called TargetNeutral.com. Here's how it works: Consumers basically pay to pollute. They calculate how much CO2 emissions are coming out of their tailpipes and then pay a commensurate amount toward renewable energy projects in places like India and Mexico.

The goal is to create a zero-sum game, where programs like those that capture methane from animal waste supposedly offset the driver's CO2 emissions. Projects like these have made BP a sweetheart among environmentally conscious investors. But analyst Susan Viets with Innovest Strategic Value Advisors says BP's black eye from the recent pipeline shutdown in Alaska has sent many of those investors running.

SUSAN VIETS: I mean, you just need to look at the share price to see what's happening. It dropped 5.5 percent shortly after the announcement into the Prudhoe Bay shutdown. And it hasn't recovered. Today it was trading at 69.5, so it's was up marginally but it's just not back up where it was before the announcement.

Viets speculates that BP may have sped up the launch date of its new website to focus attention back on its sustainability efforts. But some are questioning whether carbon offsets offer the best bang for the buck.

Mark Trexler is president of Trexler Climate and Energy services, which analyzes the carbon offset market. He says BP is jumping on a bandwagon that has exploded in recent months. But whether it'll save the planet is another matter.

MARK TREXLER: A lot of the stuff that is being sold through those websites is questionable in terms of whether you're truly reducing emissions and neutralizing your emissions.

Trexler says these guilt-driven carbon offset programs have value, it just may be more educational than environmental.

People go to websites and learn about how their actions may be contributing to global warming. But he says in the case of BP, TargetNeutral.com comes up short.

I'm Sam Eaton for Marketplace.