Environmental Site Offers Donors 'Stock' Option

By Sam Kean

Reduce, reuse, recycle — and, now, retire. The Clean Air Conservancy plans to add a fourth R to the familiar three by allowing people to purchase "carbon credits" — stocks that regulate how much carbon dioxide companies emit — and donate them to a charitable fund that holds the stocks, essentially retiring them.

On the "climate exchange," companies that emit greenhouse gases are allotted a certain number of credits, each worth one ton of emissions,