Trevor
For what its worth in the UK domestic air does not seem to be worse than any other domestic transport although in the short term it is probably better to use air to avoid a new road or (worse?) a new railway.
In the great picture however I do not think domestic air is much of an issue. even if it expanded it would be a very small source of emissions. Long distance travel involves emmitting a lot of carbon by any mode. As the IPCC report shows Aircraft Emissions at high altitude (plus 9 km) have greater impact than the same volume of emissions at low altitude. I think the issues are what technical alleviation is possible and how little long distance travel will we accept.
