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Climate change is a change in the "average weather" that a given region experiences, including such factors as storm frequency, temperature, wind patterns and precipitation. The rate and magnitude of global climate changes over the long term have many implications for natural ecosystems. As society becomes increasingly reliant on energy consumption in work at home and for mobility, the heat-trapping nature of the atmosphere has increased. As our scientific understanding of this situation increases, so does public concern and the requirement for a policy response. Aviation contributes a small but growing proportion to this problem (less than 4% of man-made atmospheric emissions). A key factor however, is that some of aviation's emissions are emitted in the upper atmosphere and may have a more direct effect. The science of climate change is still relatively new and the future is uncertain. However, there is a broad consensus that policy needs to be enacted now if climate change related problems and costs are to be avoided.
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Many countries have ratified The Kyoto Protocol which is an amendment to the United Nations Framework Convention on Climate Change (UNFCCC). These countries commit to reduce carbon dioxide and five other greenhouse gases, or engage in emissions trading if they maintain or increase emissions of these gases. A total of 141 countries have ratified the agreement. Notable exceptions include the United States and Australia. The Kyoto protocol was negotiated in Kyoto, Japan in December 1997, opened for signature on March 16, 1998, and closed on March 15, 1999. The agreement came into force on February 16, 2005 following ratification by Russia on November 18, 2004. It is likely that commitments to Kyoto, and emerging science and growing concern about the effects of emissions and contrails in the upper atmosphere, will raise aviation's profile on the international climate change policy agenda.
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How does aviation affect climate change? |
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Aircraft perturb the atmosphere by changing background levels of trace gases and particles and through condensation trails (contrails). Aircraft emissions include greenhouse gases such as CO2 and water vapour that trap terrestrial radiation and chemically active gases that alter natural greenhouse gases, such as O3 and CH4. Particles may directly interact with the Earth’s radiation balance or influence the formation and radiative properties of clouds.
Aircraft “Contrails” are lines of ice crystals that are formed by the aircraft disturbing the air in certain conditions (e.g. moisture content, temperature etc) with some contribution from combustion exhaust. It is now widely believed that these contrails can trigger the formation of cirrus clouds which thus affect climate. In 1992, aircraft contrails were estimated to cover about 0.1% of the Earth’s surface on an annually averaged basis with larger regional values. Contrails tend to warm the Earth’s surface, similar to thin high clouds. The contrail cover is projected to grow to 0.5% by 2050 at a rate which is faster than the rate of growth in aviation fuel consumption.
Closer to the ground, airport related operations also contribute to climate change, though emitters such as aircraft, passenger transport trips, airfield ground transport, airport buildings and airfield systems. Below 1,000ft aviation related emissions also affect air quality which is covered elsewhere. Measures to improve climate change impact at heights of less than 1,000ft above the ground, may also have an air quality benefit. This is subject to trade-offs as covered in the air quality section.
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More information |
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How can climate change affect aviation? |
Policy regarding aviation and climate change is still being considered, particularly in Europe. Domestic aviation is already included in national KYOTO related emissions inventories and some larger airports have had national emissions obligations imposed. Similarly, aircraft engines are already subject to ICAO emissions standards aimed at reducing fuel use and hence CO2 emissions (also see potential implications for air quality and trade-offs).
It is not possible to predict the nature or extent of the eventual policy response, however options being considered for European application include emissions trading, restrictions and fuel surcharges. Other potential policy factors could include:
- Greater stimulus for imposed and demonstrable operational improvements such as efficiency, and climate optimised routes;
- Greater impetus for framework changes that optimise the use of existing capacity (airspace and aircraft);
- Greater emphasis on inter-modality especially for mainland short haul routes;
- The necessity to safeguard air transport for society through restrictions elsewhere.
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In addition to the policy response, climate change itself may also have direct and indirect effects on aviation; for example:
- More severe weather patterns (winds, storms and visibility) affecting capacity or efficiency;
- Shifting route-demand patterns due to changes in preferred destination;
- Water shortage constraining airport development;
- Sea level rises affecting low lying airports;
- Changing wind directions affecting runway configuration;
- Changes to winterisation requirements;
- The suppression of demand phenomenon cause by major catastrophe;
- Economic burden caused by climate change may reduce potential disposable income and hence propensity to travel.
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As yet the outcomes are uncertain!
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How is climate change quantified? |
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This is one of the greatest uncertainties facing society. Whereas there is broad consensus that climate change is an issue for mankind, some scientists strongly disagree with this view and amongst those that do agree that climate change is an issue there are differences in the proposed degree of change.
In terms of global climate change itself, this is measured using a term "radiative [climate change] forcing" effect which tries to describe the net effect of both the positive and negative climate change effects of an emission, i.e. to account for the fact that some emissions may have both global warming and global cooling effects. Quantifying these complex climate effects requires a combination of chemical science to work out how different pollutants inter-react and complex atmospheric models to see how changes might happen.
A major assessment of aviation’s climate effects has been undertaken under the auspices of the UN’s Intergovernmental Panel on Climate Change in its report “Aviation and the Global Atmosphere”, commissioned by the International Civil Aviation Organisation and the World Meteorological Organisation. Extract:
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Bar charts of radiative forcing from (a) all perturbations in 1990 (from IPCC, 1996) and (b) aviation effects in 1992. Note scale change from (a) to (b). In (b), best estimate (bars) and high-low 67% probability intervals (whiskers) are given. No best estimate is shown for the cirrus clouds; rather, the dashed line indicates a range of possible estimates. The evaluations below the graph are relative appraisals of the level of scientific understanding associated with each component.
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National aviation related emissions estimates (which are aimed at quantifying the amount of emissions rather than the affect this has on climate), are typically undertaken but converting fuel use into carbon dioxide or by extrapolating fuel use from flight data (such as that stored by EUROCONTROL).
There is also a growing trend for individual stakeholders to calculate and report their climate change emissions and to look for ways of voluntarily reducing their emissions, before legislation bites.
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How can aviation’s effects be managed? |
As mentioned previously, there are a number of policy options being considered at governmental level and, instruments such as ICAO engine emission standards are helping to reduce aircraft fuel use and greenhouse gas emissions. However, other than general efficiency aims and, because the science on the relative climate effects of altitude, contrails and NOx is not yet fully understood the evaluation of potential policy solutions with the certainty of a positive result is incomplete.
Nevertheless there is a lot that can be done to conserve fuel which in-turn reduces climate change forcing effects:
- Making routes more direct;
- Aiming for a fuel optimised flight profile;
- Increasing load factor and the capacity (and use) of more fuel optimised routes;
- Operating more fuel efficient aircraft;
- Avoid holding and queuing aircraft with engines running (in the air and on the ground);
- Avoiding noise restrictions and procedures that do not achieve sufficient benefit compared to the other environmental disbenefits;
- Using effective fuel optimised speeds when circumstances change;
- Using the other potential management options in the air quality section.
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Some guidance on mitigation exists already such as:
- the ICAO Circular 303, AN 176:
“Operational opportunities to minimize fuel use and emissions” and
- the IATA document:
“Guidance Material and Best Practices for Fuel and Environmental Management” published Dec 2004
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Last validation: 11/07/2007
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