After a while I let this issue slide for a while, until my dear friend Laurence forced it firmly back into my consciousness again, with some challenging questions.
Here is the answer as best as I can find out, though I would welcome any more information or discussion - please add your comments to this post.
Using travelnotes.org I calculated that the round trip distance is 43,000 Km. According to information I found it would require 24 trees to be planted in order to offset the carbon dioxide produced for one person to travel this distance.
So in order to account for this trip, over the next twelve months I will plant 50 trees - and then keep a watchful eye to give them the best chance of surviving and growing to healthy oxygen-producing, carbon dioxide-locking trees, over the coming years.
"In 1999 the world's leading climate scientists estimated that 600 million tonnes of carbon dioxide a year was pumped into the earth's atmosphere through flying," says Graham Simmonds, chief executive for Trees for Cities. "
To put it another way, flying accounts for 3.5 percent of mankind's contribution to global warming, so it is serious business." Flying business class also leaves a larger carbon footprint, since executive seats take up a lot more space in an airplane -- Simmonds believes the footprint is up to 50 percent larger than sitting in economy.
One option is to offset emissions by planting trees that absorb carbon dioxide. For a round trip from London to New York, which covers 11,000 kilometers (6,200 miles) and produces 1.4 tonnes of carbon dioxide, you need to plant six trees. For a short haul return flight from Auckland to Wellington, a distance of 1,300 kilometers, you need two trees to absorb the 250 kilos (550 lbs) of carbon dioxide.