It is clear that air travel is a significant contributor to global climate change. Studies indicate that aviation is currently responsible for 3% of global carbon dioxide emissions and air travel is only becoming more and popular. In 1999, the Intergovernmental Panel on Climate Change (IPCC) reported that air plane greenhouse gas emissions will increase tenfold between 1992 and 2050. Traveling 2,000 miles in an airplane emits approximately the same amount of carbon dioxide as driving 1,900 miles in a mid-sized car. However, Greenhouse gases emitted from airplanes have particularly damaging effects because of the altitude at which gases are released.

These disheartening numbers may compel you to look into purchasing carbon offsets along with your next plane ticket. Fortunately, there are currently dozens of companies through which individuals or organizations can neutralize their carbon emissions from flying. Such offsets can take multiple forms: investing in renewable energy (such as wind, biomass or solar), energy-efficiency projects (such as compact fluorescent lights, refrigerators) or biological sequestration (such as planting trees that will uptake carbon). There is a range of quality and standards amongst carbon offset companies, yet, there is currently no universal regulatory body governing the way in which companies use consumers' money. As such, it is up to consumers of these voluntary offsets to do their homework and ask lots of questions before choosing a company that they believe will most effectively offset their carbon emissions. When making this decision for yourself, you may want to check out company websites and send a few e-mails to find the answer to some of the following questions:

Is the carbon-offset company a non-profit or not? What percentage of their sales go towards operating costs? You may feel that you're getting the most bang for your buck if a high percentage of your money is going directly towards offset projects. Non-profits generally put more money directly towards projects (as opposed to operating costs). However, it is not entirely clear how different companies define "project implementation" funds versus operating cost funds.

What sorts of projects do they invest in? Renewable energy and energy-efficiency projects avoid emissions, whereas as sequestration projects absorb emissions that have already entered the atmosphere. Sequestration projects generally deal with the land use. This can be a little bit of a bargain as it can be difficult to predict what sort of diseases or human activity will plague a forest in the future.

If the company is investing in projects that would be carried out regardless of your financial support or receives renewable energy credits for a project, in addition to selling you offsets, then you are not actually offsetting your emissions. Such a company would not be worth your money.

You may also be interested in knowing if the company invests in projects in its own country or in developing nations. Projects in developing nations are sometimes desirable because they are often less expensive to carry out. They are also controversial because foreigners end up carrying out the cheaper emissions reductions, leaving the developing nation with only costly projects to carry out in the future.

Do they subscribe to third party standards? If so, what kind? There are various third party or internationally recognized criteria that some companies choose to follow. Because this is such a new business, it may be wise to buy only from companies that abide by the strictest certification and verification standards, even if this makes them more expensive. The Voluntary Gold Standard is one of the most thorough standards available.

How do they calculate air travel emissions? Some companies have you simply enter the number of miles you flew, others asks for origin and destination information and still others do more complicated calculations that deal with the altitude at which the plane was flying. You may want to explore a variety of options, depending on how greatly you value simplicity over accuracy, or vice versa.

Are they transparent? It is generally desirable for the company to make this information readily available.

While it may seem like a daunting task to find out which carbon emission offset company makes the most sense to you, keep in mind that once you settle one, you probably will not have to do such thorough research again for quite some time.
Here are a few companies (recommended by the Tufts Climate Initiative) to get you started:
Atmosfair

Climate friendly
Myclimate
NativeEnergy

How much do they cost? A roundtrip ticket for Minneapolis to New York City (2400 miles of air travel) would cost about $12.00 to offset if you were to purchase offsets from Native Enery. Considering the ticket costs about $200, the cost of offsets is (in effect) a small, 6% tax that will make your flight emissions free.

To learn about more offset companies and more details on how to evaluate them check out "Voluntary Offstes For Air-Travel Carbon Emissions" by the Tufts Climate Initiative in 2006.

Photo by Flickr user Steelepop used under a Creative Commons license