I was delighted to see your cover story "The sin of air travel" by Ben Parfitt [August 9-16]; it gave a good introduction to this key aspect of global heating.

Though the magnificent Heat by George Monbiot was quoted, the key message on air travel was omitted. The global ration of CO2 emissions that just might be sustainable is under three tonnes per person per year.

One transatlantic return flight, with the added warming effects of height and contrail damage, uses up more than a whole year's ration. We have to stop flying.

As for "offsetting", this disgusting, cynical avoidance of responsibility is simply like telling a rapist to carry on raping as long as a donation is made to the local rape-crisis centre. By all means plant trees, but don't believe for a moment that their planting obviates the need to change our behaviour.

> Stephen Hill / North Vancouver

CO2 emissions caused by air travel amount to fewer than four percent of U.S. emissions and fewer than two percent worldwide. Car travel is more than four times as big a factor, and transportation is second to industry (mostly electricity generation). So it won't help much to shut down the airlines. It might help to get people out of their cars, which would solve a lot of other problems.

> Greg Tomkins / North Vancouver