From the Summary: "Forests are major carbon sinks (storehouses), and activities that alter forests can release or sequester carbon dioxide (CO2), the most common greenhouse gas (GHG). Some carbon markets have been formed under mandatory GHG reduction regimes, such as the Kyoto Protocol and various regional and state initiatives in the United States. Other markets have formed for voluntary efforts to reduce GHG emissions. Offsets, or credits for sequestering carbon or reducing emissions in unregulated sectors, are typically allowed in both mandatory and voluntary markets. Forestry activities are among the largest-volume and lowest-cost opportunities for generating offsets."
CRS Report for Congress, RL34560
National Agricultural Law Center: http://nationalaglawcenter.org/