My wife and I recently decided we could not, in clear conscience, make a trip to London merely to attend a wedding.  We were both sure that the cost to the planet of such whimsical continent-hopping must be unsustainable, but had no real idea just much energy it takes to move one adult from Johannesburg to London by air (approx 9000kms or a quarter of the way around the world).  We'd love an answer expressed in everyday terms like say tumble-drier-hours, or 100W lightbulbs burning, etc.

Tim Greene Johannesburg