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condenses into ice crystals in the cold, dry, upper-level air—it’s not unlike the fog that results when you exhale on a cold day. Contrails are clouds, you could say. Water vapor, strange as it might sound, is a byproduct of the combustion within jet engines, which is where the humidity comes from. Whether a contrail forms is contingent on altitude and the ambient atmospheric makeup—mainly temperature and something known as vapor pressure.
    I refuse to devote valuable page space to the so-called “chemtrail” conspiracy theory. If you know what I’m talking about and wish to argue the matter, feel free to email. If you don’t know what I’m talking about, don’t worry about it.
Much is being made of air travel’s impact on the environment, particularly with respect to emissions. Is it possible to reconcile frequent flying with a pro-planet consciousness?
    This is a tough one for me. I’m probably greener than most people, abiding best I can by the three Rs of good stewardship: reduce, reuse, recycle. I don’t own a car, and much of the furniture in my apartment was scavenged from curbsides and refurbished by hand. I’ve replaced my incandescent light bulbs with compact fluorescents. Then I go to work and expel hundreds of tons of carbon into the atmosphere. Am I a hypocrite or what?
    Commercial aviation is under increasingly virulent attack for its perceived eco-unfriendliness. In Europe especially, powerful voices have been lobbying for the curtailment of air travel, proposing heavy taxes and other disincentives to restrict airline growth and discourage people from flying. (“Binge flyers” is the derogatory nickname for Europeans who take advantage of ultra-cheap airfares to indulge in short-stay leisure junkets.) How much of this outcry is fair and how much is gratuitous airline-bashing is debatable. Airlines are easy targets these days, but in the hierarchy of environmental threats, they are perhaps disproportionately villainized.
    I’m the first to agree that airlines ought to be held accountable for their fair share of ecological impact, but that’s the thing: globally, commercial aviation accounts for only about 2 percent of all fossil fuel emissions. Commercial buildings, for one, emit a far higher percentage of climate-changing pollutants than commercial planes, yet there is little protest and few organized movements to green them up. It’s similar with cars. Americans have staggeringly gluttonous driving habits, yet rarely are we made to feel guilty about them. U.S. airlines have increased fuel efficiency 70 percent over the past thirty years, 35 percent since 2001 alone, mostly through the retirement of fuel-thirsty aircraft. Average fuel efficiency of the American automobile, on the other hand, has stayed stagnant for at least three decades.
    The sticking point, though, is that the true measure of aviation’s environmental impact goes beyond simple percentages. For one thing, aircraft exhaust—containing not only carbon dioxide, but also nitrogen oxides, soot, and sulfate particles—is injected directly into the upper troposphere, where its effects aren’t fully understood. Separately, experts contend that the presence of those aforementioned contrails propagates the development of cirrus clouds. Clouds breed clouds, you could say, and cirrus cover has increased by 20 percent in certain traffic corridors, which in turn influences temperature and precipitation. As a rule of thumb, experts recommend multiplying that previously cited 2 percent fossil fuel figure by another 2½ to get a more accurate total of the industry’s greenhouse contributions. Using this formula, airlines now account for about 5 percent of the problem.
    That’s still not much, but civil aviation is growing rapidly around the world. China alone is planning to construct over forty large airports. In the United States, the number of annual