California regulators have approved four categories of carbon offsets in its soon-to-launch cap-and-trade program: forestry, urban forestry, ozone depleting substances, and agricultural methane.

FORBES: Using Carbon Credits To Pay For Energy Retrofits

They say the case for limiting carbon emissions is every bit as strong as it was for lead, or for ozone-depleting chemicals, or other substances that have been regulated by the EPA over the last three decades.

NPR: Supreme Court Hears Global Warming Arguments