Sustainable transport | The impacts of aviation

This post may be very controversial. The impact of flying on the environment is important. However, I am not here to imply that you should stop having your holiday abroad in the sun [who doesn’t like that?!] or travel to meet your friends and family. The only purpose of the present post is making you aware of the big impact that flying has on our planet, and so just suggesting you to have a little thought when you book your tickets. I am myself very ‘guilty’ in this sense; I live far from my family and travel quite often to meet them. So again I am not here to judge you or ask you to commit not to fly; only fly responsibly.

You can read a couple of personal stories about people who chose not to fly, but then reconsidered their choice. Here and here. I think they’re very insightful.

The contribution of aviation to total UK GHG emissions (including international transport) is not as large as other sectors such as energy and road transport. However total aviation emissions have doubled (a 104% increase) since 1990, while emissions from road transport have increased by only 2% and emissions from the other large contributors have fallen. As a result aviation’s share of total UK GHG emissions has tripled from 2% in 1990 to 6% in 2009.

This is due to the fact that aviation has experienced a rapid expansion as the world economy has grown. Passenger traffic has grown since 1960 at nearly 9% per year, while freight traffic, approximately 80% of which is carried by passenger airplanes, has also grown over the same time period.

One of the most damaging effect of aviation on the climate is that aircrafts emit gases and particles directly into the upper troposphere and lower stratosphere where they have an impact on atmospheric composition. These gases and particles have different effect that contribute to climate change:

1.   They alter the concentration of atmospheric greenhouse gases, including carbon dioxide (CO2), ozone (O3), and methane (CH4);

CO2 emissions constitute over 98% of GHG emissions from aviation. The estimated GHG emissions associated with an average flight are:

The NOx emissions from subsonic aircraft in 1992 are estimated to have increased ozone concentrations at cruise altitudes in northern mid-latitudes by up to 6%, compared to an atmosphere without aircraft emissions.

2.   They also trigger formation of condensation trails (contrails, the long artificial clouds that sometimes form behind aircraft).

Contrail photo by Nilson Menezes on Fotopedia

In 1992, aircraft line-shaped contrails are 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. This faster growth in contrail cover is expected because air traffic will increase mainly in the upper troposphere where contrails form preferentially, and may also occur as a result of improvements in aircraft fuel efficiency. Contrails are triggered from the water vapour emitted by aircraft and their optical properties depend on the particles emitted or formed in the aircraft plume and on the ambient atmospheric conditions.

3.    They may increase cirrus cloudiness. 

Cirrus photo by Mykola Swarnyk on Fotopedia

Extensive cirrus clouds have been observed to develop after the formation of persistent contrails; these has been positively correlated by some studies. About 30% of the Earth is covered with cirrus cloud. On average an increase in cirrus cloud cover tends to warm the surface of the Earth. An estimate for aircraft- induced cirrus cover for the late 1990s ranges from 0 to 0.2% of the surface of the Earth. This will possibly increase by a factor of 4 (0 to 0.8%) by 2050.

Technology advances have substantially reduced most emissions per passenger/km. Subsonic aircraft produced today are about 70% more fuel efficient per passenger/km than 40 years ago. However, the technological advances have been counteracted by the steep expansion of the aviation sector. Therefore, technology will not fully offset the effects of the increased emissions resulting from the projected growth in aviation of the future years.

I hope you liked this little bit of information, based on the review of a couple of reports. I’d like to leave you with a little song. Flying by Seize the day.

So do you fly? Would you like to reduce the amount of flying you do? Do you think the idea is right or a little insane? I am really interested in your opinions!

References:

Penner, J. E., D. H. Lister, et al. (1999). Aviation and the Global Atmosphere. Summary for Policymakers. A Special Report of IPCC Working Groups I and III, in collaboration with the Scientific Assessment Panel to the Montreal Protocol on Substances that Deplete the Ozone Layer, IPCC.

RCEP The environmental effects of civil aircraft in flight, Royal Commission on Environmental Pollution.

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