From national governments to media companies such as News Corp. to food growers, organizations of all stripes are going carbon neutral by reducing and offsetting emissions. The desire to buy offsets for the emissions that can't be eliminated has created a "green rush" of new offset companies, but a lack of standards is confusing consumers and endangers trust in a market that today is largely based on faith.

The ideal of having a carbon footprint of zero -- emitting no more greenhouse emissions than you sequester -- became so popular in 2006 that "carbon neutral" was recognized as the word of the year, and the idea continues to flower.

The desire to go carbon neutral can stem from many things: genuine environmental concern, financial considerations (as fewer emissions often equal greater operating efficiency), generating positive PR, or even alleviating personal guilt. Regardless of the motivation, the demand for carbon offsets has ignited commercial and non-profit organizations to fill the void.

More than 40 organizations around the world now sell or participate in the carbon offset market, including the U.S. Forest Service and investment house Morgan Stanley. Carbon offset sellers decide what if any third-party oversight is involved, which has prompted concerns about the quality of the offsets. In response, the Federal Trade Commission will reportedly investigate the nascent industry.

But just as global warming has its naysayers, so does the carbon offset market, with some comparing writing a check to compensate for one's carbon footprint to the Catholic Church's former practice of selling indulgences to remove sin. Fox News' Sean Hannity has contradicted the company line in speaking out against offsets, while parody site "Cheat Neutral enables straying spouses to offset their indiscretions.

Guilt-Free and Easy

Americans on average create approximately 21 tons of carbon emissions per person each year, compared to a global average of 4.5 tons, according to Trexler Climate and Energy Services. Carbon offsets are priced between $4 and $20 per ton, so for somewhere between $100 and $400, individuals can (at least in theory) counter their annual carbon emissions.

Offsets are growing in popularity partly because they provide a feeling of being environmentally conscious without a change in lifestyle or business practices. By purchasing a carbon offset you can "buy yourself out of making harder choices," says Anja Kollmuss, the outreach coordinator at Tufts University's Tuft's Climate Initiative.

Finding a company to sell you an offset is easy, but understanding the environmental value or quality of an offset can be as complicated as mastering the federal tax code. Carbon offsets fall into two general categories: the reduction (or prevention) of future carbon emissions, or the sequestering (storing) of carbon that has already been released into the atmosphere. Most carbon offset sellers use a variety of sources and types of projects and disclose the information on their websites

Developing clean energy sources that do not emit carbon or implementing improvements in energy efficiency are the most common projects that offset providers fund. For example, offset seller Climate Trust is participating in an truck stop electrification project, according to marketing and communications manager Jed Jorgensen. The group partnered with transportation company ShurePower to provide charging stations to run the electrical systems of trucks that are at rest. Instead of idling their trucks for several hours and burning diesel fuel, the trucks are plugged into electric outlets that produce much less carbon per hour than a truck engine, Jorgensen says. The project is only economically feasible because of the selling of the carbon offsets, he says.

Sequestration projects plant vegetation or trees to take the carbon out of the atmosphere take several years to reach their maximum ability to reduce the carbon in the atmosphere. Carbon offsets that sponsor sequestration projects will be described as future emissions reductions on the sellers' websites. These projects can counter deforestation and provide a wildlife habitat, but according to Tufts' Kollmuss "sequestration projects are not a great way to reduce carbon."

For example, it is difficult for carbon offset sellers to guarantee that the forests are permanent, since they could be destroyed by fire or harvested, Kollmuss says. Therefore, offsets based on future reductions might never occur. A study of offset programs that she co-authored does not recommend tree planting offsets "because of all the uncertainties involving bio-sequestration projects."

Where the trees are planted can also make a difference in their ability to counter climate change. A recent study by the Carnegie Institution found that trees added to the tropics help to cool the earth while trees planted in snowy areas can absorb more sunlight and warm the area rather than reflecting the light.

Next: Ranking offset providers.