Image copyright AP Image caption Global emissions from aircraft are forecast to continue to grow until the middle of the century

Researchers have identified a new way to produce aviation fuel from sugarcane biomass that could deliver substantial cuts in greenhouse gas emissions.

The source crops could be grown on marginal land, avoiding displacing food production, the team observed.

They added the development of renewable liquid fuels was critical to reduce global reliance on petroleum and help mitigate climate change.

The findings appear in the Proceedings of the National Academy of Sciences.

Biofuel sweetspot

"We've identified a new route of chemistry with its source from sugars in sugarcane plus some of the so-called waste material called bagasse," said co-author Alexis Bell from the University of California, Berkeley, US.

"We show in this paper how we can put these components together to make jet diesel and lubricants."

Image copyright Aircraft (Image: Reuters) Image caption Commercial flights have been able to use biofuel since 2011

The development of a reliable biofuel that can be scaled up to a level that be used by the world's commercial airlines has proved somewhat elusive.

Prof Bell explained that there were a number of understandably strict requirements when it came to aviation fuel.

"The first one is that there must be no oxygen content, the reason being that any oxygen you put in decreases the energy density and as space on an aircraft is at a premium, and you'd like to pack in as much energy in the form of burnable fuel as possible," he told BBC News.

"Second, the fuel must have the right boiling point distribution, and then it has to have properties called lubricity, which means it does not cause excessive wear of the turbine components.

"It also has to have a very low pour point, which means the temperature at which the fuel becomes gelatinous and therefore no longer flows. When you are up in the stratosphere, temperatures around the aircraft are around -40C (-40F) or -50C, so you do not want your fuel gelling up on you."

He added: "What we have developed meets all of those criteria."

The carbon cost of flying

Image copyright Getty Images

Eight million of us fly every day and this number is increasing.

In 2012, 2% of all human carbon emissions were result of plane emissions.

If air travel continues to grow at the predicted rate, it could contribute a considerably higher proportion by 2050.

Is jet travel becoming the dirtiest way to cross the planet?

The search for aviation biofuels broke on to the public stage in the late 2000s when there were a number of test flights using a blend of conventional fuel and biofuel.

In February 2008, the first commercial flight partly powered by biofuel (derived from a mixture of babassu nuts and coconuts) took off from London's Heathrow airport.

After a lengthy review by aircraft makers, engine manufacturers and fuel producers, biofuels were approved for commercial use in 2011.

Prof Bell said the team were hopeful that their findings would ultimately be adopted by commercial fuel producers.

"Our sponsors, BP, have encouraged us to apply for a patent, which we have, on this technology," he revealed.

"Where they see the likely commercial interest for themselves and others is that the lubricants would be first as the profit margins are largest, next would be aviation fuel because of the growing US and European regulations requiring a 'green' component of aviation fuel."

Food v fuel

In recent years, political support for biofuels has waned as concern grew that global demand for biofuels would result in a switch away from food production to biofuel production, exacerbating food security worries.

Prof Bell acknowledged that certain crops as feedstock for the sugar-derived process would be problematic: "If, for example, we were to use sugar beet instead of sugarcane then there would be a potential conflict over fuel versus food."

But he added: "By using sugarcane, particularly in Brazil, on land that is not used for agriculture, we escape that conundrum.

"But we are talking about the Amazon basin, and one of the issues there is that if you cleared the land of scrubs and trees - whatever is growing there naturally - in order to make it available for growing sugar plantations, and you get rid of that vegetation by burning it then you are putting a big pulse of CO2 into the atmosphere."

Prof Bell said that the process to make the aviation biofuel outlined in his team's paper would use waste biomass to generate the energy required operate the refinery, with excess energy being put into the Brazilian grid system.