A decade on from the setting of three key goals to reduce climate-change impact, the Air Transport Action Group (ATAG) says the sector is "tracking ahead" of the short-term objective to improve fuel efficiency by 1.5% a year from 2009 until 2020.
However, it admits that ability to meet medium- and long-term targets is heavily dependent on action from governments and other stakeholders.
And, with no guarantee that emissions can be reduced at a rate commensurate with rapid growth, the sector faces increasing pressure to consider curtailing its expansion until decarbonisation becomes a more realistic prospect.
In 2008, airline association IATA said that in addition to the 1.5% fuel efficiency goal, it would work towards achieving carbon-neutral growth from 2020 and halving net CO2 emissions by 2050, relative to 2005 levels.
"We're tracking quite some way ahead [of the short-term target]," says ATAG executive director Michael Gill, noting that the global annual average improvement is closer to 2.1%. "We're pretty confident that we will continue to track ahead of 1.5% to 2020, when the carbon-neutral growth target sets in."
But according to the International Council on Clean Transportation, aircraft fuel-efficiency improvements have been slowing down in recent years and are being "outstripped by more travellers taking to the sky". In its latest Transatlantic Airline Fuel Efficiency Ranking study, released in September, the ICCT said the carbon intensity gap between the most efficient carrier, which it identifies as Norwegian, and the least efficient – British Airways, according to the data used in the report – had increased to 63% in 2017 from 51% in 2014.
"New policies to accelerate investments in more fuel-efficient aircraft and operations are critical if industry is to meet its long-term climate goals," says the ICCT.
While the group does not dispute the 2.1% overall efficiency improvement figure touted by the airline industry, the report's co-author Brandon Graver points out that this relates to the difference between 2009 and 2017, but says the sets of numbers used by IATA and the ICCT both "point to decreasing efficiency gains in recent years".
The industry's medium-term carbon-neutral growth target is achievable, says Gill, but only if ICAO's Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) is implemented smoothly. This will require "commitment from the government side to make sure that states are ready", he notes.
"If those commitments are made then I believe CORSIA will [enable the industry to] meet our carbon-neutral objectives."
But while "from the industry side there is a level of CORSIA preparedness", Gill admits that not all governments are as prepared as they could be when it comes to putting in place the necessary reporting and oversight processes. "The first of January 2019 [when airlines must begin monitoring and reporting their carbon-dioxide emissions for CORSIA] is just around the corner. I think there are governments in many parts of the world that are very up-to-speed, but there are gaps in knowledge in certain regions," says Gill.
To address this, ATAG and IATA are, he says, conducting a "widespread capacity-building exercise" to arm states with the information they need to ensure their airlines can participate in the market-based measures. Questions still remain, however, over the types of offsets that can be used to comply with CORSIA.
A question mark also hangs over the airline industry's ability to achieve its 2050 goal of halving carbon-dioxide emissions from 2005 levels. Turning this ambition into reality "requires ongoing commitment on the technology and alternative aviation fuels side", says Gill.
Even if this does happen, some question whether the goal in itself goes far enough. The chair of the Energy Transition Commission, Jonathan Adair Turner, told delegates attending this year's Global Sustainable Aviation Summit in Geneva that the air transport sector must achieve zero net emissions without the use of carbon offsets. He said this would require high carbon pricing to encourage airlines to shift towards sustainable fuels in greater numbers.
And, to ensure that sustainable fuels are available in sufficient quantities by 2035 and beyond, work needs to be done now. "We need to see agreements in place for supply in the next few years because the impact won't be seen until years down the line," says Gill. "This is not some far-off, distant aspiration – it's a very real objective that we're pushing the industry to move ahead with now."
Momentum is building, however, and a number of recent alternative-fuel announcements from airlines show that progress is being made, albeit slowly. For instance, United Airlines in September operated what it says was the longest transatlantic flight to be partially powered by sustainable aviation fuel.
The carrier operated its San Francisco-Zurich service using a Boeing 787 fuelled with a 30/70 biofuel/kerosene blend, with biofuel supplied by AltAir Fuels. United has publicly committed to reducing its own greenhouse-gas emissions by 50% by 2050 – by expanding its use of alternative fuels, operating more fuel-efficient aircraft and implementing additional operational improvements.
September also brought an announcement from JetBlue Airways that it had signed a 10-year renewable jet fuel purchase agreement with bioenergy firm SG Preston. JetBlue describes the deal as "the largest long-term binding commitment by any airline globally for HEFA-based [hydro-processed esters and fatty acids] renewable jet fuel".
JetBlue says that, in its blended form, the total amount of renewable fuel to be purchased by the airline is equivalent to roughly 20% of its annual fuel consumption at New York JFK airport.
"We're seeing more and more examples [of airlines using sustainable fuels] and we're pushing airlines to [sign] brave, long-term offtake agreements," says Gill.
But the environmental promises the industry has made are not enough to placate opponents of air transport expansion. On 1 October, a campaign group called Stay Grounded published a 13-point plan aimed at curbing the growth of the aviation sector. In a paper setting out its stall, the group said that while "future technical improvements for aircraft and operations have been identified and should continue to be researched", they will be "insufficient to overcome aviation’s emissions problems".
The pressure group is calling for a moratorium on airport construction and expansion, and for the removal of what it sees as "privileges" enjoyed by the airline industry, such as tax breaks on kerosene. In its position paper, Stay Grounded says: "The forecasted efficiency gains in fuel use are exceeded by historic, current and planned growth rates of air travel and air freight. Step changes in aviation technology are uncertain and will not come into effect until decades from now.
"Given the urgency of emissions reductions, relying on questionable scenarios like a sector-wide introduction of electric planes is too risky and diverts focus away from the immediate emission cuts needed. For the decades to come, decarbonised air traffic or 'carbon-neutral growth' will, therefore, remain an illusion."
The airline industry is at pains to emphasise the benefits that air travel brings to the global economy. In its latest Aviation: Benefits Beyond Borders report, for instance, ATAG says aviation supports 65.5 million jobs globally and $2.7 trillion in global economic activity.
But it is clear that there is a growing conundrum over how much growth should be allowed to a sector which brings so many economic and social benefits but has an increasingly detrimental effect on the environment.