The International Air Transport Association revised down its estimates for the production of sustainable aviation fuel after finding that projects are so far failing to deliver fast enough.

In a briefing at its annual meeting in Dubai, IATA said that it now sees 51 million tons of cumulative renewable fuel capacity by 2030, down from the 63 million tons it initially estimated in December. IATA made the adjustment after examining projects it tracks and finding many of them aren’t where they need to be to produce sufficient fuel by the end of the decade.

“This is really what’s going to be ready by 2030,” IATA’s Director of Net Zero Transition Hemant Mistry said. “Part of what we’re trying to do is build a foundation for what the airlines will use and we need to make sure that’s credible in the first place.”

Airlines are facing increasing pressure to decarbonize, with sustainable aviation fuel, or SAF, currently seen as the main short-term solution to reduce emissions. However supply of the fuel is nowhere near what it needs to be, with airlines often struggling to secure sufficient amounts.

IATA sees SAF production tripling this year to 1.5 million tons, but that will only be 0.5% of the total industry’s fuel needs. The body said that production must increase by a factor of 1,000 by 2050, a huge challenge but one that’s achievable with strong and urgent public policy support.

“That sounds like it’s really almost not possible, but the thing is the world has achieved these types of challenges many times over in the past,” IATA Chief Economist Marie Owens Thomsen said.