Key questions hanging over ICAO's forthcoming Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) include not just whether the airline industry will be ready in time, but whether the carbon markets will be able to cope with the high level of demand for offsets from their newest customer.

With deadlines looming for airlines to submit their emissions-monitoring plans before phase one of the global market-based measure takes effect in 2021, there is much focus on how well-prepared carriers will be for their participation in the scheme. But equally important is ensuring that there are enough high-quality units available for airlines to purchase in order to offset the industry's post-2020 increase in carbon dioxide emissions and enable it to achieve its medium-term target of carbon-neutral growth.

"It is estimated that CORSIA will generate demand for 167 million tonnes [worth of carbon offsets] per year, so aviation is going to be a big buyer of emissions units," Michael Adam, senior manager aviation environment at IATA, told delegates attending the Aviation Carbon 2017 conference in London in early December.

"Roughly a couple of dozen airlines [already] have voluntary carbon offsetting programmes [of their own], but this is very far from covering the 1,000 operators under CORSIA."

Adam says this raises "a number of questions and concerns", and asks: "Will the carbon markets be ready in time?"

Airlines will find themselves in competition for units with other sectors that are under pressure to reduce their emissions as states work to honour the commitments they signed up to under the 2015 Paris climate-change accord. According to Jochen Gassner, a member of the executive board at sustainable business consultancy First Climate, this could lead to "a situation of constrained supply".

There is also uncertainty as the industry waits for ICAO to finalise the emissions unit criteria (EUC) that will guide airlines' decisions on which type of offsets to buy. Clarification on this is expected to happen by the middle of 2018.

Experts on how carbon markets work say it is up to the airline industry to stimulate the supply of offsets needed to satisfy demand.

"The aviation industry will have to go out there and develop the market," says Gassner. "Don't assume the supply will be there and don't assume it will be as cheap as it is today." He adds that the airline industry "needs to get its act together" and create new demand for carbon offset units.

The type of projects commonly funded by the sale of offset units include those related to renewable energy, reforestation, methane destruction and the provision of fuel-efficient cooking stoves to households in developing nations. In addition to offsetting emissions elsewhere, such projects can "provide socioeconomic benefits to countries" when done correctly, says Gassner.

Wayne Sharp, chief executive of carbon trading specialist Global Environmental Markets (GEM), believes that CORSIA presents a "big opportunity" for airlines to help stimulate the carbon market and "bring it back to life". He advocates the development of a centralised process that could simplify the procedure for airlines to buy their offsets.

"I believe the aviation sector could have a centralised exchange," says Sharp, adding that this would create "fair market access for all", enable transparency, and reduce costs. Having "one place to go electronically" to buy offset units could negate the need for airlines to have "a separate registry in each country [they] operate to", he argues. Such an exchange "could be run by the industry".

"You have an opportunity to be at the front of solving the [climate change] problem that we have," says Sharp. "You guys could create $1 billion-worth of offsets for the industry."