This could be a valuable find for landowners. Although it is not yet common in North America, emissions trading has been gaining popularity in parts of Europe. Also known as cap and trade, emissions trading works to reduce pollution by setting a limit on the amount of pollutants an organization can emit into the air. If they exceed that number, the group is required to obtain carbon credits. One carbon credit equals one metric ton of carbon-dioxide or other equivalent greenhouse gases. Carbon credits can be purchased in a variety of ways. Such as: planting new trees or harvesting old wood that has stored carbon; collecting methane from landfills; or purchasing credits from other companies who have a carbon surplus by staying below their emission requirements. This week, the California Air Resources Board announced the consideration of a large plan to fight global warming. The recommendations include reducing emissions, in part by requiring major polluters to trade carbon credits. "Farmers can sell the carbon they have stored in their trees through a carbon credit stock market," Guyette said. "Companies that emit excess of carbon would be able to buy carbon credits to offset their pollution