Aboard the world's biggest cargo ship

Global shipping contributes about a billion tonnes of CO2, more than the entire economies of Germany or the UK.

The International Maritime Organization says moving goods by ship is 80-100 times more efficient than by air.

But the Scandinavians are taking ships' emissions seriously.

Roger Harrabin was given a tour of the Estelle Maersk, the world's biggest container ship, which its owners claim is the most efficient in the world.