The head of global airlines’ biggest trade group implored oil producers to make more low-emissions aviation fuel, warning the future of commercial air travel depends on the industry’s successful decarbonization.

Sustainable aviation fuel is the best available tool for cutting emissions, International Air Transport Association Director General Willie Walsh said at an aviation summit in Singapore Monday. Demand for the cleaner-burning fuel far outstrips supply, even though it can cost three to five times more than conventional jet fuel.

“Every bit of fuel that gets produced would be used because this is an existential issue,” Walsh said. “This industry will not be allowed to grow unless we can prove to our customers, regulators, governments, people in general, that we can grow in a sustainable manner.”

After surviving the pandemic, airlines’ biggest challenge is reaching a goal to have net zero carbon emissions by 2050. While the sector currently accounts for a relatively small portion of global emissions, it faces huge challenges to decarbonize and could see its share balloon in coming decades if its rate of progress falls behind other industries. An estimated $5 trillion of capital investment may be needed to make the transition, much of it to build sustainable fuel refineries.

Walsh also warned that hydrogen won’t be a viable alternative form of propulsion any time soon, underscoring the importance of increasing production of sustainable aviation fuel.

Sustainable fuel, which can be made from waste oils and agriculture feedstock, can cut carbon emissions by as much as 80%. But its higher price has also raised the question of who needs to bear the cost — Walsh says it’s an extra expense that passengers can’t avoid, while Singapore is set to introduce a fuel levy that could raise ticket prices.

Beyond sustainability, Walsh said the industry is also likely to face supply-chain snarls that have held up new aircraft, engines, and spare parts for a few more years.

“There will be significant numbers of aircraft grounded through 2024 and into 2025,” he said. “It’s very, very difficult for airlines to plan when there’s great uncertainty around when these challenges will be overcome.”