Aviation & carbon emissions: pressure grows for net zero


School strikes by students in support of government action on climate change; a new popular environmental campaign (Extinction Rebellion) occupying central London for 11 days in Apr-2019; a near 40% increase in Green MEPs after recent European Parliamentary elections. Concern for the environment, in particular climate change, is widespread and mainstream.

Before the IATA AGM in Seoul on 1-3 June 2019, the airline trade body's CEO Alexandre de Juniac called 2019 "a very big year for sustainability". In Jan-2019, airlines started tracking CO2 emissions ahead of the 2021 start of the aviation offsetting scheme, CORSIA. In Oct-2019, ICAO's Assembly will consider standards for CORSIA's implementation.

The scheme is taking years to devise and implement and has required huge coordination and collaboration between governments and aviation industry participants. CORSIA will be an important tool in meeting aviation's target to stabilise emissions at 2020 levels pending the technological breakthroughs needed to meet its target to halve emissions by 2050.

However, this now looks weak compared with the UN goal to eliminate net carbon emissions by 2050. Growing public concerns about climate change could challenge the long term sustainability of aviation. The industry must fully align itself with the more ambitious target.


  • Aviation's carbon emissions are relatively small but growing and their impact is increased by altitude.
  • Aviation's climate change mitigation targets and strategy led the world when adopted more than a decade ago.
  • Fuel efficiency is improving, but CORSIA is a stopgap to carbon neutral growth. New technology is needed for the long term.
  • Aviation is not included in the UN's more ambitious targets, but faces growing pressure to adopt net zero emissions by 2050.

Aviation's carbon emissions are relatively small but growing…

According to the United Nations sixth update of its Global Environment Outlook, published in Mar-2019, aviation is a small but growing contributor to global emissions. Referring to IEA data for 2017, it said that aviation accounts for less than 2% of anthropogenic CO2 emissions. However, this would rank it among the top 10 global emitters worldwide if aviation were a country.

Moreover, growth in aviation means that its emission are increasing. ICAO has estimated that aviation's 2020 emissions will be 70% higher than in 2005 and could increase by a further 300%-700% by 2050 without any action. Aviation could then be responsible for between 4% and 15% of CO2 emissions.

…and their impact is increased by altitude

A further reason for aviation's high profile in terms of climate is that aircraft emissions at altitude have a bigger impact than those emitted near the earth's surface. This means that aviation's impact on climate change is higher than its share of CO2 emissions, perhaps by a factor of two according to some estimates.

In addition, aircraft also emit water vapour, other gases and aerosols that trigger cloud formation and modify natural clouds and alter greenhouse gas concentrations in the upper atmosphere.

Aviation has climate change mitigation targets and a strategy

Global aviation led the world in setting climate change targets, doing so more than a decade ago. The industry continues to be guided by these goals aimed at mitigating its climate change impact.

These are a short term goal of 1.5% pa fuel efficiency improvements from to 2020, a medium term goal of carbon neutral growth from 2020 (maintaining net CO2 emissions at 2020 levels) and a long term goal to halve its net emissions by 2050 versus 2005.

Its strategy to achieve these goals consists of four pillars: operations, infrastructure, technology and a global market based economic measure.

Fuel efficiency is improving (but emissions are still growing)

Aviation has outperformed against its short term goal, achieving a 2.3% pa improvement in fuel efficiency. Compared with 1990, fuel burn per flight has halved. This has mainly been achieved through new, more efficient aircraft technology.

However, this means that, if traffic growth is 5% pa, fuel consumption and CO2 emissions are still growing, albeit at the slower rate of 3% pa.

CORSIA is a stop gap to carbon neutral growth

The market based measure adopted by ICAO is the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA). It is aimed at addressing any increases in total CO2 emissions from international civil aviation above 2020 levels through the purchase of offsets from approved carbon reduction projects.

This should help the industry with its medium term goal to stabilise net emissions at 2020 levels, but is really only a stop gap pending more radical solutions.

New technology is needed for the long term

The long term goal of halving net emissions by 2050 requires technological step changes in areas such as biofuels, new propulsion systems such as electric power plants and new airframe design concepts.

Research is being carried out in these areas, but there has yet to be a major break through.

The UNFCCC coordinates global action on climate change

At a global level, action on climate change is generally coordinated through the United Nations Framework Convention on Climate Change (UNFCCC), established in 1992 and subsequently developed through a series of other agreements and amendments.

This culminated in the Dec-2015 Paris Agreement and the Dec-2018 Katowice Climate Change Conference to agree implementation rules.

In an opinion piece published in the Financial Times on 29-May-2019, UN Secretary General Antonio Guterres stressed the importance of achieving the UN's goal of limiting global warming to 1.5C by the end of the century.

In order to accomplish this, the UN targets a 45% reduction in carbon emissions by 2030 and net zero by 2050 (versus 2010).

Public awareness of climate change has become mainstream

The Katowice Conference was addressed by the then 15 year old student activist Greta Thunberg, who inspired the school strike for climate movement. Ms Thunberg has been a significant participant in an increasingly active, confident and vocal environmental movement in Europe and globally.

Net zero emissions by 2050 is becoming an increasingly accepted target. Rebellion Extinction is calling for net zero by 2025 and is now turning its attention to aviation, with a plan to use drones to disrupt Heathrow Airport this summer.

In recent months, climate change campaigners have further raised public awareness of climate change, moving it up the collective agenda. Even if some of the methods used by campaigners are unconventional, they have undoubtedly contributed to a growing sense that concerns around climate change are now mainstream.

Aviation is not included in the UN targets, which are more ambitious

Aviation (together with international shipping) is not included within the UNFCCC and so not covered by the Paris Agreement.

This is because it is not easy to apportion aviation to a particular country, as international flights begin in one nation, end in another and may traverse the airspace of several more. ICAO is the UN body with oversight for aviation and which coordinates the sector's actions on climate change.

However, the UN targets for other sectors on carbon emissions are more ambitious than those currently used by aviation. In the international shipping industry, the Danish company Maersk has voluntarily adopted a target of net zero carbon emissions by 2050, in line with the UN target.

Aviation is one of the few global sectors to have set ambitious emissions reduction targets under its own initiative and did so long before the Paris Agreement. However, it now risks the perception that it has been let off the hook.

Aviation faces growing pressure to adopt net zero emissions by 2050

The ever increasing profile of climate change in the public consciousness will increase pressure on aviation to reach for more ambitious goals.

The UN's Mr Guterres may not have specifically had aviation in mind when he called on governments to shift taxes from people to carbon ("We should tax pollution, not people," he wrote in the Financial Times).

However, governments often display a taste for imposing taxes on air passengers to raise revenue and justifying this with vague references to environmental concerns. Concerns over the environment are also often cited to block much needed aviation infrastructure developments.

Almost every casual conversation about an individual's climate change impact will include guilty references to flying before mention of higher polluting contributions from energy, for example.

The more often the wider UN target of zero emissions by 2050 is repeated, the more aviation's halving target will look half hearted.

Mr Guterres will host a UN Climate Action Summit in Sep-2019 in New York to seek plans from national governments on how to achieve the goals of a 45% reduction by 2030 and net zero by 2050. Aviation is not part of this framework, but such events will further highlight that fact.

If aviation wants the public (who, after all, elect the politicians that appoint the regulators) to renew its licence to grow, it must increase the ambition in its climate change targets and be more demonstrative in communicating progress towards achieving them.

Aviation should also adopt the target of net zero emissions by 2050, rather than merely halving them. Moreover, it must find a way to catalyse greater and faster progress in the development of the technologies necessary to achieve this.

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