Trends in Emissions that affect Climate Change

The first ICAO Global Environmental Trends were presented and endorsed at the 37th Session of the Assembly, and since then the updated global environment trends have been developed and presented to every Assembly Session to form the basis for their considerations and decisions.

As part of the CAEP/11 (2019) update to the ICAO Global Environmental Trends, a range of scenarios was developed for the assessment of future fuel burn and GHG emissions trends.

Scenario 1 for fuel burn and CO2 emissions includes the operational improvements necessary to maintain current operational efficiency levels, but does not include any technology improvements beyond those available in current production aircraft. Scenarios 2 (low technology) assumes fuel burn improvements of 0.96% per annum for all aircraft entering the fleet after 2010 and prior to 2015, and 0.57% per annum for all aircraft entering the fleet beginning in 2015 out to 2050, in combination with additional fleet-wide CAEP/9 IE operational improvements. Scenarios 3, 4 and 5 (moderate, advanced and optimistic technology) assume fuel burn improvements of 0.96%, 1.16% and 1.5% per annum respectively for all aircraft entering the fleet after 2010 out to 2050, in combination with the latest operational initiatives, e.g., those planned in NextGen and SESAR, and additional fleet-wide CAEP/9 IE operational improvements.

Scenario 1 for NOx emissions considers no new aircraft technologies and maintains the baseline operational efficiency, which is sufficient to meet the unconstrained forecasted demand. Scenarios 2 and 3 assume moderate and advanced aircraft technology improvements, and achievement of 50% and 100% respectively of the CAEP/7 IE NOx Goal by 2036 with no further improvement thereafter, in combination with CAEP/9 fleet-wide operational improvements.




International civil aviation, as shown in Figure 1, consumed approximately 160 megatons (Mt) of fuel in 2015. By 2045, compared with an anticipated increase of 3.3 times growth in international air traffic (expressed in revenue tonne kilometres), fuel consumption is projected to increase by 2.2 to 3.1 times compared to 2015, depending on the technology and ATM scenarios. The long-term fuel burn from international aviation is lower by about 25% compared with the prior trends projections presented to the 39th Session of the Assembly. This lower fuel burn projection can be attributed to a combination of more fuel efficient aircraft entering the fleet, as well as a reduction in the forecasted long-term traffic demand. The 1.37% long-term fuel efficiency computed herein includes the combined improvements associated with both technology and operations. The individual contributions from technology and operations are 0.98% and 0.39%, respectively.

Climate Change Trends Fig 1.pngFigure 1 – Conventional Fuel Consumption from International Aviation, 2005 to 2050, Including Potential Use of Sustainable Aviation Fuels

* Illustrative case would require high availability of bioenergy feedstock, the production of which is significantly incentivized by price or other policy mechanisms; **100% replacement with sustainable aviation fuel would require a complete shift in aviation from petroleum refining to sustainable aviation fuel production and a substantial expansion of the agricultural sector, both of which would require substantial policy support.




Significant uncertainties exist in predicting the contribution of sustainable aviation fuels in the future. However, a number of near-term scenarios evaluated by AFTF indicate that up to 2.6% of fuel consumption could potentially consist of sustainable aviation fuels by 2025. This analysis also considered the long-term availability of sustainable aviation fuels, finding that, by 2050, it would be physically possible to meet 100% of international aviation jet fuel demand with sustainable aviation fuels, corresponding to a 63% reduction in emissions. However, this level of fuel production could only be achieved with extremely large capital investments in sustainable aviation fuel production infrastructure, and substantial policy support. The effort required to reach these production volumes would have to significantly exceed historical precedent for other fuels, such as ethanol and biodiesel for road transportation. The effect of such an expansion in the use of sustainable aviation fuels on net CO2 emissions from international aviation is shown in Figure 2.

Climate Change Trends Fig 2.pngFigure 2 – Net CO2 Emissions from International Aviation, 2005 to 2050, Including Sustainable Aviation Fuels Life Cycle CO2 Emissions Reductions.


Full-flight NOx emissions trends were evaluated as they have an effect on the global climate. As shown in Figure 3, in 2015, the full-flight NOx emissions of international aviation were 2.50 Mt. In 2045, the full-flight NOx emissions projection ranges from 5.53 Mt to 8.16 Mt, which represents a 2.2 to 3.3 times growth compared to 2015, against the 3.3 times forecasted growth in international air traffic. As with fuel burn, the long-term full-flight NOx from international aviation is lower by about 21% compared with prior trends projections. This lower NOx emissions projection can be attributed to a combination of aircraft with lower NOx engines entering the fleet, as well as a reduction in forecasted long-term traffic demand.


Climate Change Trends Fig 3.pngFigure 3 – Full Flight NOx Emissions from International Aviation, 2010 to 2050.

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