What's wrong with air transport? The excessive use of air travel is a problem because:

• It is one of the principal contributors to global environmental problems such as climate change, ozone depletion, and the wasteful use of scarce raw materials;
• It encourages unnecessary travel. The tourist industry encourages people are able to travel to 'exotic' locations, which must exist on an unreliable tourist income. When the area has become overdeveloped, the tourists leave, to colonise the latest 'fashionable' resort.

The construction of the second runway would lead to:

1. A largely unsustainable form of transport further encouraged;
2. Higher emissions of global warming gases and other pollutants;
3. Ozone layer destruction (in particular, from a new generation of supersonic airliners).

While the local effects of noise pollution and the destruction ofirreplaceable tracts of countryside that will be lost forever are well known, the global effects have received little publicity. This is a major problem as these are probably the most important issues surrounding air travel as we approach the 21st century.

The problem is as as much to with where the aircraft fly,as how much they emit. For example, nitrogen oxide emmissions (NOx) from aircraft account for around 3% of anthropogenic NOx emissions, yet 25-30% of total NOx in the upper troposhere could be due toaircraft emissions (note 1) (the troposhere extends to the tropopause at around 15km, and above this lies the stratosphere).

1. Promotion of an unsustainable form of transport.
Air travel consumes large quantities of untaxed non-renewable fossil fuels, and is a largely inappropriate form of internal travel. Air travel makes possible the ludicrous policy of transporting food thousands of miles, not only imposing the high environmental costs associated with air freight, but also increasing dependence on cash crop monoculture in poor countries.

2. Higher UK emissions of global warming gases.
Air travel has been estimated to contribute between 3-30% of global warming. A study conducted (Mayer Hillman, Town & Country Planning magazine, September 1996) estimated that a single transatlantic return flight emits almost half the CO2 emissions as from all other sources (lighting, heating, car use, etc.) consumed by an average person yearly. One recent study has estimated that "if the Airport grows as planned, CO2 emissions by 2020 could be greater than from all other transport in the regional catchment."

Aircraft are major sources of greenhouse gases particularly carbon dioxide (CO2), water vapour, and nitrogen oxides (NOx). We need to reduce our total carbon dioxide emissions by 60% to merely stabilise atmospheric CO2 at current levels - considering that we in the developed world already emit more than our fair share, this means that the UK has to reduce CO2 emissions by 90%.

Water vapour at high altitudes causes dual problems. Firstly it leads to an increase in cirrus cloud formation, which contributes to global warming, and secondly it reacts with NOx to destroy ozone in the stratosphere.

Nitrogen oxide in the troposhere (i.e. below the ozone layer), has a totally different effect to in the stratosphere due to the complexnature of atmospheric processes. Here it contributes to ozone formation. Unfortunately this does not help replenish the ozone layer as it is in the wrong place, but instead acts as a greenhouse gas as well as contributing to smog around airports.

3. Ozone layer destruction.
Plans for a new generation of supersonic airliners (following on from Concorde) which can travel higher in the earth's fragile atmosphere are causing concern: for example, New Scientist, 15/2/97 'Aircraft wreak havoc on ozone layer': "A fleet of 500 supersonic aircraft ... would have a direct effect on stratospheric ozone." Similar effects are suspected from subsonic aircraft currently.

Nitrogen oxide (NOx) emissions from airliners are responsible for ozone depletion in the stratosphere, and many scientists are worried that this could negate the impact of the Montreal Protocol on CFC phase-out. With the next generation of supersonic airliners imminent (supersonics fly high in the stratosphere), and with subsonics flying in the upper troposhere as well as more and more in the lower stratosphere, this problem is likely to get much worse.

Recent research has also focussed on the role of sulphur emissions (in the form of SO2 and SO3) leading to H2SO4 aerosol formation (note 2), and this may well prove as important in ozone layer depletion as the role of NOx.

It is becoming increasingly clear that the effects of aircraft on complex atmospheric processes are one of the major threats to our environment.

References:
1. Lamarque et al 1996. J. of Geophys. Res. - Atmospheres, Vol 101, No. D17, p22955-22968.
   
2. Karcher and Fahey 1997. Geophys. Res. Lett, Vol 24, No 4, p389-392.
   
3. Archer 1993. Transport Retort, 16 March.