Carbon offset programs were originally used by large corporations looking to make up for their own carbon emissions by investing in renewable energy, forest conservation, and similar projects. Over the last five years, individual consumers have been given more opportunities to invest in these programs, which are becoming more widespread and popular.

California’s biggest utility company, Pacific Gas & Electric, sponsors a program called ClimateSmart that offers its customers a chance to voluntarily contribute to the company’s investments in carbon offsets. This week, PG&E announced that it bought 200,000 tons of certified forest carbon dioxide (CO2) emissions reductions from The Conservation Fund as part of the program.

Under the ClimateSmart program, customers pay a separate amount on their monthly energy bill, based on their calculated energy use. Currently, about 18,000 PG&E customers are signed up for the program, and donate an average of $4.50 per month. The company invests this money in environmental projects that reduce greenhouse gas emissions. In this case, the emissions reductions will be generated over the next five years through sustainable forestry on Garcia River Forest, which The Conservation Fund owns and manages. The Garcia River Forest is the largest, and one of the first forest-based projects supported by ClimateSmart.

Carbon trading based on tree growth is one of the most common offset programs, and it relies on the fact that growing trees absorb carbon dioxide through photosynthesis. When more trees are preserved, more carbon is stored in the forest, thus reducing emissions. Redwood forests, like the Garcia River Forest in Northern California, are great investments because they store more carbon per acre than any other forest type on earth.

As part of the deal, the Conservation Fund will harvest the Garcia River Forest less aggressively than is allowed, and sell the excess carbon stored in protected trees in the form of carbon emissions reductions. Currently, that excess is about 77,000 tons of CO2 per year, and The Conservation Fund is finalizing forest-based sales of carbon emissions reductions totaling more than 500,000 tons over time.

If you aren’t a PG&E customer, and want to participate in a carbon offset program, there are a number of organizations that have set up similar plans, including Atmosclear, the Carbon Fund, Drive Neutral, and e-Blue Horizons.