The current findings related to aviation emissions and climate change are summarized in the White Paper On Climate Change Aviation Impacts On Climate: State Of The Science, published in the ICAO Environmental Report 2016. 

This white paper highlights that the understanding and confidence in aviation climate forcings would be enhanced by a new international scientific assessment, such as the

IPCC Special Report on Aviation and the Global Atmosphere (1999).

While this new international scientific assessment is not available, ICAO has compiled a list of supplemental references that are connected with the IPCC 1999 Report topics, as follows.

1.     Aircraft emissions and the environment.

a) overview of emissions and their role in climate change, including CO₂ and non-CO₂ emissions.

The ISG White paper on "Aviation Impacts on Climate" provides a general overview of aircraft emissions (including CO2 and non-CO₂ emissions), and how they affect climate change.

References:

• Aviation Impacts on Climate: State of the Science, ICAO Environmental Report 2016, pags. 99-107.

2.     Emissions scenarios

In 2013, ICAO published the first results of trends in fuel burn and CO₂ emissions from international aviation, which showed that total global aircraft emissions that affect the global climate were expected to increase, but at a rate slower than aviation demand. In 2016, the ICAO Environmental Trends were updated, which included the consideration of possible benefits from the use of alternative fuels.

References:

• ICAO A38-WP/26, Present And Future Trends In Aircraft Noise And Emissions, 18/07/13.

• ICAO A39-WP/55, Present And Future Trends In Aircraft Noise And Emissions, 18/07/16.

• ICAO A41-WP/93  Present And Future Trends in Aircraft Noise and Emission, 31/08/22.

3.     Aviation impacts on climate

a) impact of aircraft emissions on atmospheric ozone

b) aviation Produced aerosols, contrails and cloudiness

The ISG White paper on "Aviation Impacts on Climate" provides the "state of the science" on the aviation impacts on Climate (including effects from ozone, aerosols, contrails and cloudiness).

References:

• Aviation Impacts on Climate: State of the Science, ICAO Environmental Report 2016, pags. 99-107.

4.     Potential climate change from aviation

a) how do aircraft cause climate change?

b) radiative forcing

The ISG White paper on "Aviation Impacts on Climate" provides a summary explanation on aircraft impacts on climate change. With regards to radiative forcing, a self assembled group of scientists has been working on an assessment of the potential climate change from aviation and this should include a revised estimate of the radiative forcing climate effects from international aviation.

References:

• Aviation Impacts on Climate: State of the Science, ICAO Environmental Report 2016, pags. 99-107.

• Self-assembled group of scientists (ongoing work)

5.     Aircraft technology

a) Aircraft and engine technology

b) Aviation fuels

c) Small aircraft, engine and APUs

d) Supersonic transport aircraft

Two Independent Expert Reviews (IEs) assessed aircraft technologies for CO₂ emission reduction. In 2010, the IEs developed medium- and long-term goals for aviation fuel burn reduction from technology. In 2018, updated goals are being developed as part of the Independent Expert Integrated Review (IEIR), which is considering technology interdependencies in terms of fuel burn, engine emissions, and noise.

On aviation fuels, in 2016 CAEP have developed a detailed estimation for potential alternative jet fuel usage in the short- and long-term and associated GHG emissions reductions. Additionally, the second ICAO Conference on Aviation and Alternative Fuels, in 2017, agreed on an ICAO Vision on Aviation and Alternative Fuels, which calls on States, industry and other stakeholders for a significant proportion of conventional aviation fuels to be substituted with sustainable aviation fuels (SAF) by 2050. The meeting documentation also provides general updates on the status of the alternative fuels industry.

References:

• CAEP/10 Short-Term And  Long-Term  Alternative Jet  Fuel  Production And  Associated  GHG Emissions Reduction (2016)
• ICAO Doc 9963, Report of the independent experts on the medium and long term goals for aviation fuel burn reduction from technology, Montréal, 2010.
• ICAO Doc 10127 - Independent Expert Integrated Technology Goals Assessment and Review for Engines and Aircraft
• ICAO Second Conference on Aviation and Alternative Fuels, Mexico City, 11 to 13 October 2017. 

6.     Air transport operations

a) ATM

b) other operational factors (aircraft performance, inter-modal transport, ground emissions)

Improved operations and Air Traffic Management (ATM) offer potential improvements in efficiency and ICAO analysis has shown that full implementation of the aviation system block upgrade (ASBU) Block 0 could achieve 0.7 to 1.4 per cent fuel saving in 2018 compared to 2013. Modules within Block 0 include, amongst others, Optimised Approach Procedures including vertical guidance, improved operations through enhanced en-route trajectories, and improved flexibility and efficiency in descent profiles using Continuous Descent Operations (CDO).

References:

• ICAO A39-WP/55, Civil Aviation and the Environment, 30/06/16

• ICAO A41-WP/93, Civil Aviation and the Environment, 31/08/22

7.     Mitigation pathways and regulatory measures.

a) international framework in the context of the UNFCCC

b) international framework in the context of ICAO

Concerning regulatory measures, work in ICAO led to the adoption of Annex 16 Vol III – Aeroplane CO₂ Emissions, the world's first global design certification standard governing CO₂ emissions for any industry sector, and also Annex 16 Vol IV – CORSIA, the world's first global emissions-offsetting scheme for any global industry sector. These two elements are part of the ICAO "basket of measures" designed to achieve the ICAO global aspirational goal of keeping the global net CO₂ emissions from international aviation from 2020 at the same level.

References

• Annex 16 Vol III - Aeroplane CO2 Emissions

• Annex 16 Vol IV – Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA)

• ICAO Assembly Resolution A41-20 - Consolidated statement of continuing ICAO policies and practices related to environmental protection – General provisions, noise and local air quality

• ICAO Assembly Resolution A41-21 - Consolidated statement of continuing ICAO policies and practices related to environmental protection – Climate change

• ICAO Assembly Resolution A41-22 - Consolidated statement of continuing ICAO policies and practices related to environmental protection – Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA)

8.      Future Scenarios

a) current inventories

b) future scenarios

Future emission scenarios are covered by the ICAO work on Environmental trends.

References:

• ICAO A38-WP/26, Present And Future Trends In Aircraft Noise And Emissions, 18/07/13.

• ICAO A39-WP/55, Present And Future Trends In Aircraft Noise And Emissions, 18/07/16.

• ICAO A41-WP/93  Present And Future Trends in Aircraft Noise and Emission, 31/08/22.