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The website of Citizens for a Greener Evanston (greenerevanston.org) explains that when Evanston signed the U.S. Mayors Climate Protection Agreement in 2006, it “pledged to ‘meet or beat’ the Kyoto Protocol by reducing greenhouse gas emissions to 7 percent below 1990 levels by 2012. A 2007 inventory conducted by the City showed that, in order to meet this goal, Evanston must reduce its GHG emissions 13 percent by 2012.”

This article is one in a series that suggests ways that individuals or businesses can reduce their carbon footprints.

For many Evanstonians, air travel is the biggest source of personal carbon emissions. A couple of business trips to New York, two visits with the grandchildren in Los Angeles, and a vacation in Florida will add the equivalent of six-and-a-half tons of carbon dioxide (CO2) to an Evanston traveler’s carbon footprint. And for some, this itinerary would be just a warm-up.

Serious frequent flyers who measure their carbon footprint will find that emissions from their air travel easily dwarf emissions from their home energy use and driving. Annual U.S. average per capita emissions are about 4.0 tons CO2 from residential energy use and 3.8 tons CO2 from driving.

Climate Impact of Air Travel

Although air travel currently contributes only3 percent of total U.S. carbon emissions, its climate impact is considerably greater than that of the emissions alone. In addition to emitting CO2, airplanes (1) release nitrous oxide, which produces the powerful greenhouse gas ozone, (2) trigger the formation of contrails, and (3) cause increased cirrus cloud cover – all of which contribute to climate change.

Although more research is needed to fully understand the effect of aircraft emissions at high altitudes, the Nobel-prize-winning Intergovernmental Panel on Climate Change estimates that the climate impacts of flying are about 2.7 times greater than that of the CO2 emissions alone.

This additional warming effect is referred to as “radiative forcing,” and many carbon calculators apply a radiative forcing multiplier in calculating the carbon footprint of air travel.

Lower-Carbon Options

When it comes time to travel, then, there are some options. According to a recent report from the Union of Concerned Scientists – Getting There Greener: The Guide to Your Lower-Carbon Vacation – the “carbon bargain” is the motor coach. This holds true for short trips and cross-country trips, for solo travelers, couples and families of four.

The next best option? For trips of up to 500 miles, the train is a good low-emission choice – except for a family of four, who are better off driving.

For longer trips, flying economy is the greener alternative for solo travelers and couples, but driving still yields a smaller carbon footprint for a family of four.

Air travelers can reduce the carbon footprint of their trip by following these tips:

• Fly economy. Business and first-class seats take up more room than economy seats, thereby reducing the number of people the flight can carry. This makes a passenger traveling in business or first class responsible for more emissions than a traveler in coach – twice as much, for example, for a first-class passenger on a domestic flight.