The offsets are likely to come from projects like wind farms and methane capture facilities.

At present the annual carbon dioxide emission from the authority's operation of its facilities is 298,000 tonnes while the figure from public use is 5.07m tonnes.

The port authority has an existing commitment to reduce its impact, which includes the emissions of planes at its airports, cars at river crossings as well as ships, by 5% a year and by 80% by 2050.