There is a growing realisation that climate change is a reality and not a myth. Air travel is now the fastest-growing contributor to global warming, and avoiding a flight when there are easy alternatives is probably the biggest single thing that any individual can do to cut their carbon footprint and limit their own impact on the environment. No wonder many people are now looking for less environmentally-hostile ways to travel.

It's not an exact science, and I'm certainly no expert, but Eurostar has done its homework and commissioned independent research to assess the CO2 per passenger produced by a London-Paris Eurostar journey versus that emitted by a passenger on a London-Paris flight. The research looked at actual Eurostar passenger loadings, actual Eurostar power consumption, the way Eurostar's electricity is generated, actual aircraft loadings, actual aircraft fuel consumption, and so on. The conclusion was remarkable: Taking the train to Paris instead of flying cuts CO2 emissions per passenger not just by 10% or 20% or even 50%, but by a staggering 90%...

http://www.seat61.com/CO2flights.htm