Joe - we're not comparing long-haul vs. short-haul flights. Long haul flights are slightly more efficient, given the fact that the huge amount of energy required to climb up to cruising altitude is averaged out over a longer flight time.

Short-haul flights are the worst emitters of greenhouse gas, as all that energy to get up to cruising altitude is followed almost immediately by a glide down for landing. For a dramatic illustration of the impact of air travel vs.other forms of transportation, see a chart from the IPCC at http://www.davidsuzuki.org/Climate_Change/What_You_Can_Do/air_travel.asp

That's why ready alternatives to short haul flights - even driving (particularly where there's more than one in the car) - are vastly better, from a climate perspective.

If one must fly short-haul on the routes flown by Porter, and one wishes to decide which aircraft to fly based on their relative emissions of greenhouse gases, Air Canada or Westjet are clearly preferable over Porter. I'm glad you've conceded that.

No one should be flying the ancient gas-guzzlers you want us to compare Porter's Q400 to.

Brian Iler