The aviation industry is between the hammer and the anvil when it comes to meetings its net-zero climate impact obligations. Overall, aviation accounts for 2.5% of global carbon dioxide emissions, but the number continues to rise steadily year by year. Even though this sector hasn’t been included in the Paris Agreement, there were hopes that the industry was capable of self-regulating its emissions and set ‘ambitious’ targets — but that doesn’t seem to be the case.

In fact, if anything, aviation emissions are only expected to surge considering the number of people flying has doubled from 2 to 4 billion in the past 15 years and shows no sign of slowing down. Global aviation emissions have risen by 70% from 2005 to 2020, and the European Commission predicts that by the middle of the 21st century, demand for flying could increase aviation’s greenhouse gas emissions by upwards of 300% over 2005 levels if no drastic measures are taken to reduce them.

Direct carbon emissions aren’t the only problem. There’s a less-spoken dark side to the aviation industry: the production of nitrous oxide and exhaust water vapor trails (the contrails), which are responsible for two-thirds of the climate change-causing radiative forcing that comes with aviation. These non-CO2 climate effects have to be compensated by removing hundreds of millions of tons of direct CO2 from the air.

But despite this obvious trend in which emissions are rising fast rather than plummeting, the global aviation industry has nevertheless committed itself to trying to achieve net-zero emissions by 2050. How could something like this ever be possible?

A new study out of the University of California, Irvine (UCI) says this is actually a plausible scenario. There’s one catch though: it will cost $1 trillion in carbon offsetting.

The seemingly impossible challenge of achieving net zero in aviation

Researchers led by Steven Davis looked at several pathways that the aviation industry could take to reach net zero. Some of these scenarios were optimistic, taking into account several significant contributions toward net zero, including reduced demand for air travel, substituting jet fuel for biofuels, and technology improvements such as hydrogen-powered and electric aircraft.

However, it is highly unlikely that demand for air travel will fall dramatically — if anything it will continue to grow furiously in the coming decades. The only reasonable way that air travel demand may drop is if a hefty carbon tax is introduced that accounts for all the environmental damage that the industry’s emissions cause. As a result, the price of tickets could surge, double, triple, or even more, driving demand down. But taxing carbon directly at the source is highly politically controversial and I wouldn’t bet any money on that any time soon.

There are some biofuels made from plants or waste materials whose performance is comparable to today’s petroleum-based jet fuel while producing 50% to 80% fewer carbon emissions over their lifecycle. But while aviation biofuels are worth pursuing they cannot solve the industry’s problems entirely. The authors of the new study mention that covering the energy needs of the aviation industry would require doubling the world’s current production of biofuels and directing all of it toward fueling aircraft. This means setting aside as much as 3 million square kilometers of land for biofuel crops, which is equivalent to one-third of the entire size of the US. Never mind the fact that biofuels are around four times more expensive than jet fuel.

“Scaling up production of sustainable aviation fuels will entail big investments in new technologies and processes. Demand for biofuels will also be competing with food production for land, even as demand for food also increases in the coming years,” said Davis, who is the UCI professor of Earth system science. “But we are optimistic that through targeted innovation, good public policy and corporate climate action, our society can make progress toward achieving net-zero commercial aviation.”

And while entirely carbon-neutral aircraft that run on hydrogen or electricity are quite interesting and will likely become quite common, there are physical constraints that mean such aircraft can’t carry more than a few dozen people and only over short flights.

“We are beginning to see a path toward dealing generally with climate change through improved efficiencies, electrification of energy end uses and switching to non-greenhouse-gas-emitting sources of energy,” said lead author Candelaria Bergero, UCI Ph.D. student in Earth system science. “But flying will be particularly hard to decarbonize because of its appeal and popularity as a mode of transportation and its reliance on energy-dense liquid fuels.”

Per business as usual, which is the likeliest scenario out of the eight pathways explored by the researchers, the annual emissions of the aviation industry are set to triple by 2050. In order to meet net-zero targets by that date, the industry would have to spend $1 trillion on carbon offsets.

Indeed, many airlines currently offer their customers offsets, who have to pay a premium for this service on their tickets. American Airlines has a carbon offset plan in partnership with the nonprofit Cool Effect, through which customers are provided options for offsetting the carbon emissions associated with their flights. Delta Air Lines has a similar program as part of its net zero initiative.

However, offsetting never solves the underlying problem, but rather pays for the carbon footprint and passes it on to a third party. For instance, an airline might generate one million tons of CO2 in a year and will choose to pay for that carbon that is offset by a solar farm or wind turbine installation. This mechanism only works to mitigate climate change in the short term because most other industries are currently learning how to become net-zero companies, so there is no one left to dump the responsibility on their shoulders.

All is not lost though. It seems unlikely that the industry can reach net zero by 2050, but that doesn’t mean it can drastically cut down its emissions. Airlines and aircraft manufacturers want to improve aircraft energy efficiency by 2% per year, which could offset more than half of the projected growth in demand for flying. Coupled with more sustainable alternative fuels and a transition towards electric/hydrogen-powered aircraft for short-haul flights, these actions could lead to sizable gains.

“The main challenges to scaling up such sustainable fuel production include technology costs and process efficiencies, both of which are thus key targets for policies and innovation. Additionally, the interactions with food security, local communities and land use are enormous hurdles for such a ramp-up and come with their own increasingly difficult trade-offs. Yet with moderate growth in demand, continued improvements in aircraft energy efficiency and operational and infrastructure improvements, new propulsion systems for short-haul trips, greatly accelerated production of SAFs and the possibility of balancing non-CO2 radiative forcing with equivalent amounts of CDR, the aviation sector could achieve net-zero emissions by 2050,” the researchers concluded.

The new findings appeared in the journal Nature Sustainability.