Tracking Clean Energy Progress

More efforts needed

CO2 emissions from aviation continue to rise, and accounted for around 2.5% of global energy-related CO2 emissions in 2018. While energy efficiency in aviation improved by 3.2% per year between 2000 and 2014, it slowed to less than 1% per year between 2014 and 2016. In the SDS, aviation energy efficiency needs to improve by more than 3% per year to 2040. With global aviation activity continuing to grow rapidly (+140% since 2000), further international policy measures, such as more stringent carbon pricing and efficiency standards, could help put aviation on the SDS pathway.

Sacha Scheffer
Lead author
Contributors: Cyril Cassisa, Jacob Teter, Pierpaolo Cazzola

Energy intensity of international aviation

	Energy intensity	ICAO goal (2% annual improvement)	SDS
2000	18.2		
2001	18.6		
2002	19.3		
2003	19.2		
2004	18.2		
2005	18.2		
2006	17.5		
2007	16.9		
2008	15.5		
2009	15.4		
2010	14.3		
2011	14.1		
2012	13.7		
2013	13.5		
2014	13.1		
2015	13.1		
2016	12.9	12.9	12.9
2017		12.7	12.8
2018		12.4	12.4
2019		12.2	12.1
2020		11.9	11.7
2021		11.7	11.5
2022		11.5	11.1
2023		11.2	10.7
2024		11.0	10.4
2025		10.8	10.0
2026		10.6	9.7
2027		10.4	9.4
2028		10.2	9.1
2029		10.0	8.8
2030		9.8	8.5
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Notes: ICAO = International Civil Aviation Organization. RTK = revenue tonne kilometre1. Source: IEA analysis based on ICAO (2010c; 2018) and IEA (2018).

Back to Transport sector | TCEP overview 🕐 Last updated Monday, October 14, 2019

Tracking progress

Demand for air transport has more than doubled since 2000, and demand for both passenger and freight aviation is expected to remain strong in the future.

In 2018, passenger activity increased by 6.1% to 8.2 trillion revenue passenger kilometres, and the number of total air passengers reached a record 4.3 billion (ICAO, 2019a). This activity growth is a slowdown from the 7.9% increase registered in 2017, however, with regional growth rates in 2018 ranging between 4.7% and 7.3%.

Year-on-year demand growth for freight slowed substantially, dropping by half between 2017 and 2018 to 4.6%.

CO2 emissions

CO2 emissions from commercial passenger and freight operations totalled 918 Mt in 2018 (ICCT, 2019), or around 2.5% of global energy-related CO2 emissions. Passenger transport accounted for 81% of the total. Emissions from aviation have grown 32% over the past five years.

Energy efficiency

Since 2000, the aviation subsector has achieved significant energy efficiency improvements. With jet fuel representing around 20% of aviation operating costs in 2018 (Airlines for America, 2018), raising energy efficiency has long been pursued as means of improving profitability.

Globally, aviation efficiency improved by 2.9% per year during 2000‑16, whereas efficiency improvements in international aviation were only 2.2% per year, which is more than one-third lower than aviation overall (domestic and international).

Better aircraft utilisation is one of the reasons for improved energy efficiency. The rise of low-cost airlines has increased the average number of passengers per flight, lowering energy use per passenger. The average passenger occupancy rate increased by 0.6% to a record 82% in 2018 (ICAO, 2019a), and the combined passenger and freight load factor improved by 10%, to 68%, during 2008‑17 (ICAO, 2018).

Another driver of efficiency improvement is fleet renewal, as the industry is continuously acquiring newer, more efficient planes. The fuel intensity of new commercial jet aircraft fell 1.3% per year from 1968 to 2014, corresponding roughly to a doubling of efficiency (Kharina and Rutherford, 2015).

Without the efficiency improvements achieved in 2000‑16, energy demand growth would have resulted in 70% higher total energy consumption in 2016, equivalent to the total energy demand of international shipping.

Energy efficiency improvements in aviation have historically been more rapid than in most other sectors of passenger and freight transport (e.g. cars, buses and trucks, ships), but despite these achievements, the efficiency improvement rate of international aviation slowed to only 0.6% per year between 2014 and 2016. However, new aircraft designs and logistics offer significant potential to cost-effectively raise aviation efficiency.

Policy developments

Separate goals have been set for energy efficiency improvements for domestic aviation (by the UNFCCC/Kyoto protocol/Paris Agreement) and for international aviation (by the International Civil Aviation Organization [ICAO]) (ICAO, 2010a).

The ICAO has implemented several policies to help to reduce the CO2 emissions of international aviation.

In 2017, it adopted CO2 emissions standards for airplanes, to be enforced by national aviation authorities. The standards limit the emissions of new aircraft; if they are not met, planes will have to be modified accordingly (ICAO, 2017). The standards include separate targets for aircraft certified before 2020 and those certified after, and flexibility based on the mass of the aircraft. It is estimated the standards will require new aircraft entering service after 2028 to be on average 4% more fuel efficient than in 2015 (ICCT, 2017).

In 2010, the ICAO adopted a resolution targeting a 2% efficiency improvement per year between 2013 and 2050 (ICAO, 2010b).

Separate from its energy efficiency goals, in 2016 the ICAO adopted the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA). The aviation industry will initiate CORSIA in 2021, achieving carbon-neutral growth from 2020. The International Air Transport Association’s (IATA’s) longer-term goal, to cut net CO2 emissions in half by 2050 relative to 2005, has yet to be codified by the ICAO (IATA, 2019).

All ICAO member states have to implement CORSIA, so starting in 2019, for international flights only, all operators are required to report their CO2 emissions on an annual basis. As of January 2019, (79 countries collectively accounting for 77% of international aviation pkm were participating in the scheme as of January 2019 [ICAO, 2019b]).

Starting in 2021, emissions increases from international flights will have to be compensated for through carbon offsetting. Until 2026, only flights between volunteering countries will be subject to offsetting obligations, but all international flights will be affected as of 2027, except those to or from LDCs, LLDCs, SIDS and countries with a small share of aviation activity. If the carbon price is too low – anticipated by some researchers to be below USD 5 per tonne – it will likely not promote high enough in-sector reductions (Olmer and Rutherford, 2017).

The aviation industry also aims to reduce emissions by using sustainable aviation fuels. More than 170 000 commercial flights have already flown successfully on biofuel blends, and several major airlines have made long-term biofuel purchase agreements. In 2018, biofuel use was estimated at 0.1% of US jet fuel use (ICCT, 2017).

With policy support, IATA has set an aspirational target of 1 billion passengers on flights fuelled by sustainable aviation fuels by 2025.

Interest is also growing in the use of power-to-liquid fuels derived from renewable electricity (Clean Energy Wire, 2019), but reaching this goal will require policy support to increase sustainable aviation fuel production capacity and reduce cost premiums over fossil-based jet kerosene.

Along with IATA, the Air Transport Action Group (ATAG) helps co‑ordinate the commercial aviation industry to meet environmental goals (ATAG, n.d.).

To put aviation on track with the Sustainable Development Scenario (SDS), an annual decrease of more than 3% in specific energy consumption (energy per RTK) is necessary up to 2030. Several policy and technology measures could be taken to accelerate CO2 emission reduction in aviation.

Efficiency measures applicable to passenger aircraft

Various energy efficiency measures could help align aviation with the SDS trajectory.

Potential year of introduction Lifecycle CO2 emissions reduction per aircraft
Business as usual:
Retrofits to existing aircraft 2018 4-5
New-generation aircraft (e.g. A320NEO) 2018-2025 15
Air traffic management improvements 2025 5-10
Increasing utilisation 2018 3
Increased ambition:
Engine retrofits to existing aircraft 2018 ~15
Synthetic fuels 2020 13-26
High ambition:
Early replacements of old aircraft 2018 1-9
Next-generation aircraft 2035 30-70

Source: IEA analysis based on Schafer et al. (2015) and IEA (2018).


In the European Union, no taxes are levied on aviation fuels used in international aviation: it is exempt from value-added tax (VAT), both on inputs (fuels and aircraft) and on revenues (Korteland and Faber, 2013).

Given that fuel expenditures are a major cost of flying, airlines have a strong incentive to pursue energy-efficient technologies – and CO2 pricing could provide an additional incentive to reduce emissions.

Plus, fuel taxes based on the well-to-wheel carbon intensity of fuels, or a standard mandating gradual carbon intensity reductions of jet fuel supplied and used by various carriers, would stimulate the uptake of low-carbon fuels.

Finally, introducing and progressively strengthening CO2 pricing through a multilaterally agreed mechanism such as CORSIA would also help mitigate emissions. Some stakeholders have even argued that additional taxes (e.g. ticket taxes) should be introduced to deter aviation activity and the continued growth in passenger and freight transport.

New aircraft technologies

Achieving 3% annual efficiency improvements will also require drastically stronger ICAO fuel efficiency standards.

Research on emerging efficiency technologies suggests that the rate of fuel-burn reduction for new aircraft will roughly double in the next 15 years, reaching 2.2% annually at net savings to airlines and consumers (Kharina, Rutherford and Zeinali, 2016).

To unlock these gains, manufacturers must bring to the market new, clean sheet designs that allow for deployment of the full suite of engine and airframe technologies, rather than re‑engineerings of legacy airframes (e.g. A320neo, 737 MAX).

Additional improvements from operational measures and advanced engine and airframe designs are also possible, but targets must be revised upwards for further improvements.

Clear price and regulatory signals would help enable the transition towards more efficient flights, eventually bridging risk gaps to stimulate investment in the development of major innovations such as hybrid wing body aircraft (Kharina, 2017).

Low-carbon fuels

Increasing low-carbon fuel shares in the aviation fuel mix will require considerable RD&D investments and upscaling of more mature technologies.

Low-carbon fuel options include biofuels (already in use) and 'drop-in' electrofuels (in development).

Biofuels will need to be produced through methods that reduce GHG emissions and, more broadly, achieve other sustainability targets. Regulations are therefore needed to define the criteria used to evaluate the GHG emissions mitigation and other natural resource and sustainability goals of biofuel production. Existing standards, such as the ASTM d7566, need to be expanded, regularly updated and adopted globally.

Processes that use hydrogen produced from renewable energy together with biomass to make synthesis fuels may enable efficiency gains that reduce processing costs while increasing the share of carbon from biomass in the fuel product, thereby maximising the use of scarce biomass resources. The adoption of low-carbon fuel standards could complement fuel taxes to stimulate the uptake of advanced biofuels in aviation.

High-speed rail

Major investments in high-speed rail networks could offset rapid growth in demand for short-distance flights that take a similar amount of time by high-speed rail – typically trips of 400 km to 1 200 km (UIC, 2018).

On the basis of total trip time, high-speed rail could compete with around 17% of existing commercial passenger flights, accounting for 5% of passenger activity.

The expansion of high-speed rail corridors on the most heavily utilised and competitive routes could be promoted through well-designed policies, for instance using revenues derived from the taxation of fossil fuels in aviation to build up high-speed rail networks.

Innovation gaps

Aviation is likely to be the most difficult transport sector to decarbonise.

The largest potential efficiency gains can be obtained by completely redesigning aircraft. Considering the long lead times and investment required, such measures are unlikely to be commercialised by 2030. However, “clean sheet” wing and tube aircraft have the potential to reduce fuel burn by 40% (Kharina, 2017).

In addition to research and trials of new, more efficient aircraft designs, adoption of alternative, low-carbon jet fuels will be needed to reduce CO2 emissions. Technology and scale-up barriers in producing such fuels can be best addressed through direct support from governments, incentives and standards.

Nearer term solutions, such as improving flight routing systems and switching to hydrogen and/or electricity during taxiing, can also improve the overall efficiency of the sector. 

Shortening flight distances through better routing

Considerable fuel is wasted due to inefficient routing. While providing the same service, better flight routing could limit inefficient passenger activity growth and cut consumption by as much as 10% (IEA, 2018).

Read more about this innovation gap →

Additional resources


  1. Freight demand is measured in freight tonne kilometres, while passenger demand is measured in revenue passenger kilometres. Revenue tonne kilometre (RTK) is the aggregate of freight tonne kilometres, mail tonne kilometres and passenger kilometres, with the last converted to the specific weight per passenger, including luggage (90 kg on average between 2000 and 2016).


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Yue Huang (IATA), Dan Rutherford (ICCT), Matteo Craglia (University of Cambridge)