That's the equivalent of around 8.5 tonnes of carbon. His 18 childhood return trips from Sussex to the family cottage in the Highlands would have used another 1.8 tonnes. A dedicated environmental activist, the younger Marriott, together with his partner, Jane Trowell, are trying to live the carbon-light life, but it is far from easy. But they do have a personal computer, which uses 4kg a year for every hour of daily use. They don't have a car.
Wood produces even more carbon dioxide per kilo than coal.
On the other hand, it comes from a local, renewable source. But Marriott knows it's not the answer. Not everyone can get their energy from wood. Otherwise we'd need a forest bigger than Britain. All predictions suggest that it is the sixth generation that faces the largest challenges.