Aviation and Climate Change
Aircraft are responsible for around three percent of global carbon dioxide emissions. But emissions of nitrous oxides (NOx) and the formation of condensation trails (contrails) from water vapour at near stratospheric levels where commercial jets fly mean the actual impact on global warming is much higher – possibly as much as ten percent.
Air travel is also on the rise, with GHG emissions from international air travel jumping by almost 70% between 1990 and 2002. In China, air travel is growing by around 12% per year, and worldwide passenger air travel is increasing by 5% annually, a faster rate of growth than any other travel mode. Air freight has also been growing rapidly, though it remains a small share of total air traffic.
For an activity that is largely elective and dominated by the world’s financial elite, this has become a serious concern. Air travel has been characterized by some as an “environmental sin”, the equivalent of driving a gas guzzling sport-utility vehicle. Campaigns are underway to promote teleconferencing over international business trips, and taking holidays closer to home to avoid air travel.
Teleconferencing and minimizing unnecessary air travel often make both financial and environmental sense. But as more people in countries like China are able to afford airline tickets, worldwide air tourism travel is bound to increase. Most experts believe that humanity will take to the skies more than ever in the future, and air travel could double within fifteen years if current trends persist. By 2050, the Intergovernmental Panel on Climate Change (IPCC) believes that aircraft could account for up to 15% of the global warming impact from all human activities.
Talk is now turning to ways of mitigating air travel’s future impact on climate change, and these generally fall within two spheres: technology development, and policy mechanisms. The aircraft industry is taking the issue seriously, demonstrated last week at a meeting of the International Air Transport Association (IATA) in Vancouver.
“A growing carbon footprint is no longer politically acceptable—for any industry. Climate change will limit our future unless we change our approach from technical to strategic. Air transport must aim to become an industry that does not pollute—zero emissions,” said Giovanni Bisignani, IATA Director General and CEO.
Future airplane technologies
Passenger jet aircraft produced today are already around 70% more fuel efficient than the equivalent aircraft produced 10 years ago, and continued improvement is expected. The IATA, representing 94% of the international scheduled air traffic, reports that billions being invested in new aircraft will make its fleet 25% more fuel efficient by 2020. Continued dependence on fossil fuels (kerosene) is expected to continue, but this should drive continuous improvements in aerodynamics, weight reduction, and engine design.
The majority of efficiency improvements over past aircraft have been achieved through engine technology development. Engine improvements must balance the need for increased fuel efficiency (and decreased CO2 emissions) with reductions in NOx, water vapour, and other air pollutants. Safety, reliability, noise and cost are also issues that are considered and are often subject to regulatory requirements.
Some technology developments require tradeoffs between different emissions and performance impacts. For example, some engines use high pressure ratios to improve efficiency, but this exacerbates the NOx problem. Higher pressure ratios are likely to be a continuing trend in engine development, potentially requiring new NOx control techniques to maintain regulatory compliance.
Other aircraft developments that reduce weight, reduce aerodynamic drag or improve operations can deliver cost-savings and environmental benefits, so combining engine enhancements with body developments is one key to improved performance.
Lightweight composite materials for the majority of the aircraft structure promise significant weight reductions and fuel burn benefits. In the new Boeing 787, fifty percent of the primary structure - including the fuselage and wing - will be made of composite material, potentially reducing fuel consumption by 20%.
Other developments, such as the use of winglets, fuselage airflow control devices and weight reductions have been studied by aircraft manufacturers and could reduce fuel consumption by a further 7% says the IPCC, although some have limited practicability. In the long term, it has been suggested that new aircraft configurations such as a blended wing body (flying wing) may be necessary to achieve major improvements in efficiency.
The IATA call for zero emissions aircraft may come with technologies that are still in the early stages of evaluation: hydrogen fuel cells, biofuels, and solar power.
One study concluded that conventional aircraft designs could be modified to accommodate the larger tank sizes necessary for hydrogen fuels, but the additional weight and size would increase overall energy consumption. A lack of hydrogen infrastructure, increased emissions of water vapour, and the high cost of a hydrogen aircraft are major obstacles, but the study suggested that early implementation could come within 15-20 years.
Biofuels could mitigate some aircraft emissions, but the production of biofuels to meet the aviation industry’s specifications and quantity demands is currently untested. Ethanol and biodiesel both have properties that make them currently unsuitable for jet fuel, but companies such as Virgin are pursuing biofuels research, investigating possibilities including the use of microorganisms. Solar powered aircraft, another option raised by the IATA, are largely unexplored.
However, without the commercialization of these and other novel new technologies, annual air traffic growth is expected to outstrip efficiency improvements, resulting in a net rise in CO2 emissions of around 3-4% per year, along with increases in NOx and water vapour emissions.
One possible contributor to greater aircraft efficiency is improved air traffic management. According to the IATA, there is a 12% inefficiency in global air traffic management which could largely be addressed by three ‘mega-projects’: a Single Sky for Europe, an efficient air traffic system for the Pearl River Delta in China and a next generation air traffic system in the United States. Scientists worldwide are investigating improved air traffic management, lower flight speeds, reducing idling and other efficiencies, searching for potential emissions reductions.
Regulating aircraft emissions
In recent years, governments and international organizations have looked at policy options that could create incentives or impose requirements on aircraft operators and manufacturers to reduce emissions.
At the forefront of this push is the European Union, which has proposed that aircraft be covered under the region’s Emissions Trading Scheme (ETS). Only domestic flights are covered under the Kyoto Protocol, so international flights are currently not targeted by any regulatory emissions reduction efforts.
Under the proposal, emissions from all flights within the EU will be covered in 2011, with international flights to be included in 2012, impacting airlines based in Canada directly. The EU hopes to serve as a model for other countries, and projects that by 2020, the cost of a typical return flight within the region could rise by $3-$9 Cdn.
However, an Ernst & Young study commissioned by the airline industry projects the system would cost airlines more than 40 billion Euro from 2011 to 2022, and possibly more if the credits are auctioned as proposed by the Commission. According to European air carriers, the industry is not seeking exemption but a relaxation of the cap and free issuance of credits instead of auctioning, as auctions are voluntary for member states and other industries.
The IATA states in its climate change strategy that it prefers emissions trading to a carbon tax or other charges, but would rather participate in a worldwide voluntary scheme instead. “The challenge is for the International Civil Aviation Organization (ICAO) and its 190 member States to deliver a global emissions trading scheme that is fair, effective and available for all governments to use on a voluntary basis,” said Bisignani, advocating the development of such a system at the ICAO Assembly this September.
The EU seems set on including air travel in its emissions trading plans, so a carbon cap and trade scheme for aircraft seems inevitable. Including airlines in a global climate change agreement to replace Kyoto now seems unlikely, but as the industry grows and its impact on global warming becomes greater, there may be a push to include it along with industrial sectors.
Aircraft on the climate radar
These days, a global industry with a significant impact on climate change and rising GHG emissions is sure to be a target for regulatory or policy action as well as technology development. The air transport industry is in line for some development in this area, and in antipation airline operators, aircraft manufacturers, and governments are taking action.
Some airlines are offering customers the chance to neutralize their emissions by purchasing carbon offsets: Air Canada recently partnered with ZeroFootprint to allow online purchase of GHG credits with tickets. Domestic carrier Westjet will offset CO2 for its flights booked through its green partner, Offsetters.ca, at no extra cost.
Such actions are leading the way now, but in the future much stronger action will be required to deliver reductions in GHG emissions. For a rapidly growing industry this will take concerted efforts in a number of areas, and technology may well be the key.
With technological progress, backed by strong government policies and corporate responsibility, the world should be able to continue enjoying the benefits of air travel while minimizing climate change impacts. It may not be realistic to expect sharp absolute reductions in emissions from aircraft, but finding maximum efficiency will be a vital part of a worldwide effort from every sector to reduce GHG emissions.