ICAO is reviewing new data showing that reducing contrails will do more to help the aviation industry meet the Paris Agreement’s temperature goals than the sector’s ambitious target of achieving net-zero CO2 emissions by 2050.
The standards setting group will take up the topic of contrails and other so-called “short-lived climate pollutants” (SLCP) at its 42nd Assembly, happening now in Montreal, according to ICAO agenda documents.
Front and centre is a new report from US group International Council on Clean Transportation (ICCT) concluding that reducing CO2 will have less impact on mitigating rising global temperatures than will reducing SLCPs, especially contrails.
ICCT says the aviation sector must cut both CO2 and SLCPs to reach the Paris Agreement goals.
“SLCP controls can provide faster and cheaper reductions in Earth’s temperature response to international aviation activity than [greenhouse gas] controls,” says an ICAO White Paper from August reviewing topics to be considered at the Assembly.
“Contrail avoidance, in particular, is modelled to be the most-impactful and cost-effective lever, providing 40% of total avoided warming by 2050,” the paper adds.
An arm of the United Nations, ICAO did not respond to questions about its consideration of ICCT’s report, which that group released publicly on 23 September.
ICAO is scheduled to review the proposal on 25 September, ICCT says.
The transportation group tells FlightGlobal its analysis shows that eliminating greenhouse gases like CO2 “alone cannot align aviation with the Paris Agreement”. It says the industry must focus on reducing contrails, which will cost a “magnitude” less than widespread production and use of so-called sustainable aviation fuel (SAF).
SLCPs include contrails (the result of ice crystals formed from water vapour in jet engine exhaust), and turbofan emissions including nitrogen oxides and “black carbon”, commonly known as soot. Those materials can cause atmospheric heating over hours or days, unlike CO2, which causes warming over centuries.
“The best available scientific assessments highlight that the net warming impact of non-CO2 emissions is at least the same magnitude as that of aviation’s cumulative CO2 emissions,” ICAO’s paper says.
ICAO in 2022 set its goal for the aviation industry to have net-zero CO2 emissions by 2050. The goal was intended to help the sector comply with the United Nation’s 2015 Paris Agreement, which urges member states take steps to prevent global temperatures from exceeding 2°C warmer than a pre-industrial revolution baseline.
Toward that end, airline groups rolled out ambitious road maps, saying they will achieve net-zero CO2 by means including new technologies (such as hydrogen, hybrid and all-electric propulsion), improved operational efficiencies and use of SAF.
Promises aside, SAF remains in short supply – 0.3% of jet fuel last year, ICCT says. SAF is also exceedingly expensive, and growing crops for SAF poses land-use challenges and could impact food crops.
On the technology front, aircraft and engine manufacturers have recently walked back hydrogen and all-electric ambitions due to technological limitations.
But ICCT says the CO2 focus is way overrated.
“Overall, 85% of the avoided temperature increase is linked to SLCPs,” its report says, estimating contrails “contribute the largest share” – 40% – of the aviation sector’s contribution to warming temperatures.
“Contrail abatement technologies will would take less time to develop and scale”, and cost far less than other means, ICCT adds. “SLCP reduction emerges as a more-feasible option… in mitigating aviation’s climate impact.”
It says new analytical tools and “advances in contrails science” informed the new study.
Story corrected on 25 September to note that SAF accounted for 0.3% of aviation fuel in 2024, not 0.03%.
