What should greens do about air travel?

Is it a sin to fly to your vacation spot? The Bishop of London recently proclaimed it so. Plenty of others are increasingly critical of excessive air travel too, though not all are as strident as the Right Reverend. The trick is figuring out what’s excessive. Is it OK to fly to developing countries for on-the-ground environmental and anti-poverty work? What about travel to important international negotiations and conferences? How does one decide which meetings are “important”? And then there’s the question of occasional visits to far-flung family members and loved ones. Peter Madden sorts through the salty snack mix of this contentious issue.