Nine big companies including Amazon, Ikea and Unilever have signed up to a pledge to only move cargo on ships using zero-carbon fuel by 2040.

They hope the "aggressive" target will push the heavily-polluting shipping industry to decarbonise faster.

Cargo shipping produces one billion tonnes of climate pollution each year - as much as the country of Germany.

But critics say shipping firms are not doing enough to meet Paris Agreement goals on emissions.

The Aspen Institute - the non-governmental organisation coordinating the campaign - expects other retailers and manufacturers that rely on maritime shipping to sign up.

"Maritime shipping, like all sectors of the global economy, needs to decarbonise rapidly if we are to solve the climate crisis, and multinational companies will be key actors in catalysing a clean energy transition," said president Dan Porterfield.

"We urge other cargo owners, value chain actors, and governments to join forces with us."

The companies pledging zero-carbon shipping by 2040 are:

With about 90% of world trade moving by sea, maritime shipping accounts for 3% of all global emissions. That could rise to 10% by 2050 if the industry continues to rely on carbon-intensive fuels, experts say.

The shipping industry also produces 10-to-15% of the world's manufactured sulphur oxide and nitrous oxide emissions, which can cause respiratory illness.