Seven of the worlds biggest aerospace companies have warned that the aviation industrys drive to reach net zero carbon emissions by 2050 is at risk because of the lack of agreement on how to encourage the use of sustainable aviation fuel.

In a letter to the international civil aviation organization, the chief technology officers of boeing, airbus, rolls-royce, general electric, safran, dassault aviation, and raytheon have urged greater efforts to create conditions under which sustainable aviation fuels (saf) can be widely deployed.

They warn that without broad agreement on tools and policies to encourage the use of green fuels, energy companies would not put up the trillions of dollars of capital investment between now and 2050 required to meet the needs of the aviation industry.

The sector is divided over how best to encourage the development of sustainable fuels, which are at present three to four times more expensive than conventional jet fuel. norway, for example, has set a minimum requirement for green fuel. the eu is also considering a quota for all aircraft refuelling in the bloc.

But some airlines, such as ryanair, have lobbied hard against quotas, unless they apply to all airlines globally. others believe production should be subsidised by governments until it becomes commercially viable.

The financial questions are much more important now that the aviation industry is struggling with the biggest crisis in its history because of the pandemic. with cash preservation a priority, there is little incentive to buy more green fuel.

Moreover, sustainable fuels currently account for less than 1 per cent of jet fuel supply. warren east, chief executive of aero-engine maker rolls-royce, has said in the past that volume would have to be increased by a factor of 1,000. to be compatible with a net zero carbon future, we will still need 500m tonnes of sustainable fuels to power the aviation industry of 2050, he said.

The challenge of expanding production has left some climate change experts sceptical about the potential of sustainable fuels.

The uks committee on climate change, a government advisory body, believes sustainable aviation fuel will account for just 10 per cent of total supply by 2050. however, it accepts that sustainable fuels are still key to cutting aviation emissions in the shorter term.

Paul stein, rolls-royce cto, said a greater sense of urgency was required. we need to get to a place where each trading bloc might have its own method but we are driven by common targets so the pace can be scaled up, he said.

Neither proposed electric or hydrogen-powered planes would be sufficient to deliver carbon neutral aviation, the aerospace executives said in their letter. about 80 per cent of carbon is emitted by flights of more than 1,500km, and these technologies would be suitable for shorter journeys only.

At present we know of no single technological pathway to decarbonise long-haul flights at scale by 2050 other than...sustainable fuels, they said. therefore, the requirement for the rapid scaling of [green jet fuel] is clear.

A study published by sustainable aviation, which represents the uk aviation industry, argues that a green fuels industry could deliver about 3bn in value to the uk economy and 20,200 jobs.

The research, which was conducted by energy consultancy e4tech, argues that uk production alone would save 3.6m tonnes of co2 annually by 2038.

The sustainable fuels in use today are largely made from household, municipal or industrial waste. over their life cycle they emit up to 80 per cent less carbon.

Henrik wareborn, chief executive of the waste to fuel company, velocys, said the uk had an opportunity to take a lead in the market. the research identified humberside the location of velocyss altalto plant as one of seven promising locations for the green jet fuel industry in the uk. the region has a fantastic opportunity to establish itself as the global hub for fuelling future air travel, he said.