These calculations are intended to produce a rough estimate for airliner emissions over the North Atlantic.
No attempt was made to allow for the mix of aircraft types flying the North Atlantic. The Boeing 747/400 was taken as typical, partly because its probably the most numerous type on this route and partly because the relevant fuel consumption figures have been published for this, the most fuel-efficient model of 747. By considering it to be the typical aircraft on this route I am unlikely to overestimate the impact of aircraft emissions on the atmosphere above the North Atlantic: older aircraft are less efficient.
The 747/400 has a maximum fuel load of 216,840 litres of fuel (Boeing), which gives a nominal range of 13570 km (Wikipedia, Boeing 747 article). The Atlantic route from London to New York is 5585 km, so a flight will require 89,245 litres or 71.4 tonnes of jet fuel A. After allowing a 30% fuel contingency for emergencies, diversions or airport delays I estimate that about 50 tonnes of fuel will be burnt during a single trans-Atlantic flight. During the flight this will be converted into 69 tonnes of water and 155 tonnes of carbon dioxide. These are then injected into the atmosphere at an altitude of just over 11km, the average cruising altitude of a 747 (personal observation during flights).
New Scientist (24 Feb, 2007 p35) confirms these figures. They show that a single flight from New York to Stockholm burns 51.5 tonnes of kerosene to produce 162 tonnes of carbon dioxide and 63.8 tonnes of water, which both increase global warming. It points out that 100 Kg of carbon monoxide and 900 Kg of nitrogen oxides are also output. These are also greenhouse gases. This is in general agreement with my estimate. Evidently jet fuel contains longer chain hydrocarbons than I based my calculation on. There may be some aromatics in the mix too because they calculate that somewhat more carbon dioxide and less water is produced than I did.
The UK's National Air Transport Services, which manages air traffic in the eastern side of the North Atlantic, recorded 77,198 trans-Atlantic flights originating or terminating in the UK and 98,991 that overflew the UK on their way to or from Europe in the first six months of 2005. Adding these gives a six month total number of flights. Doubling the six month total gives the annual number of flights. This amounts to a total of 352,378 trans-Atlantic flights for 2005. Note: this underestimates the number of flights because it ignores traffic growth during the year.
Multiplying the emissions from a single flight by the number of flights in 2005 gives a current annual yield of 55 megatonnes of carbon dioxide and 24 megatonnes of water. This is injected into the atmosphere about 11 km above the North Atlantic.