—Marie in San Pedro, California

 

First, remember that offsets merely offset some of your share of emissions from a flight but don't cancel them out completely. 

 

Airlines that offer carbon offsets (not all of them do) allow you to invest in projects like wind farms in Texas and forest protection in Peru. Unfortunately, airline calculators charge too little to cover the cost of canceling out all emissions from a flight. And some ignore pesky details, like the fact that emissions have much more impact at high altitude than at ground level. More rigorous calculators, such as those at carbonfootprint.com and carbonfund.org, do consider the high-altitude factor. 

 

So to be super squeaky-clean, I say set up your own simple program. The highest estimate for airline emissions is about one pound of CO2 equivalent per mile traveled. Producing a kilowatt-hour of electricity averages a bit more than a pound of CO2 emissions, so to offset all emissions by wind power, you'd have to invest around three cents per mile traveled. Using this formula, you could invest an appropriate sum in a wind power company. (A 5,000-mile junket would run you about $150.) 

 

Note that these estimates are for economy class. If you fly first class, offset costs double because all that space for the lounging elite only holds half as many passengers as coach.