I took a look at Responsible Travel, following a link from Year Of Living Generously. Their system claims to take into account all the emissions of planes (not just CO2) and they offer a very simple calculator for working out the offsets required for a particular journey. Unfortunately it doesn’t work quite so well for our needs, as we are attempting to offset 50,000 miles (3 rountrips to the UK for Kari, 4 for me, plus 2 flights back from New York and 2 rountrips to Colorado), and there’s no obvious place to insert the number of miles should you already know it.
Renewable Choice Energy is the option selected by the Whole Foods grocery store chain (the largest purchase of carbon offset credits ever, see this entry at worthwhile magazine’s blog). Their ‘residential’ options provides monthly programs at rates of $5, $10 and $15 per month dependent on size of house. Unfortunately there is no obvious way to sign up to offset a specific number of tons or airmiles without doing a few independent calculations and gathering a bit more information than is available on their site.
Carbonfund.org, the people we used for the household emissions, offer an air travel option and calculate our 50,000 miles as equivalent to 36.22 tons of CO2, over twice our household emissions. By contrast, Native Energy calculates the same number of miles as 14.4 tons, but charges more than twice as much per ton for offsets ($12.00 vs. $5.50).
In the interests of spreading our money around a number of organizations, I opted to go with Native Energy, but a discrepancy in emissions calculations of that size certainly merits further investigation, and I’ll be trying to do that before the next time I try to offset our air miles.