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Aviation and climate change: How much of a polluter is aviation?
In the lead-up to the UNFCCC climate talks in Paris (COP21) attention is turning to the aviation industry’s contribution to global warming. The industry is currently included in the draft text for the climate talks, and is coming under increasing pressure to reduce its CO2 emissions.
As the negotiations ahead of COP21 have progressed, aviation was first included then later excluded from the draft agreement. When the music finally stopped, it was included again. However, the latest draft agreement merely notes that a solution to manage greenhouse gas emissions from aviation must be found through the offices of ICAO. The targeted reduction in the sector’s emissions mentioned in earlier drafts has been removed.
This begs one very important question: how much of a polluter is aviation? In the first of our two articles on the role of aviation in climate change, we explore how aviation has contributed to global warming.
Estimates of pollution from aviation vary, are usually very contentious and too-often appear to have no particular scientific source. The confusing facts presented by both sides of the debate, and sometimes even those on the same side, makes it difficult to move the debate forward at times.
The first thing to establish is what we should be measuring when we talk about aviation and climate change.
Many of the figures quoted about climate change refer to CO2 – carbon dioxide – emissions. However, CO2 is a subset of the greenhouse gases (GHG) that are responsible for global warming. The others are methane (CH4), nitrous oxide (N2O) and fluorinated gases. The Intergovernmental Panel on Climate Change (IPCC) estimates that CO2 emissions comprise around 80% of global GHG emissions. CO2 is also a particularly particularly damaging GHG as it lingers in the atmosphere longer than other GHGs.
Carbon dioxide is the main GHG produced by aviation. However, focussing on CO2 emissions alone (as many do) could lead to underestimate of the contribution of aviation to global warming.
Aviation also produces other GHG emissions. On a per-tonne basis, these other GHGs have more potential than CO2 to have an impact on global warming over the next 100 years. A tonne of methane, for example, is estimated to have the same warming effect over a century as between 28 to 36 tonnes of CO2. However, the smaller quantities produced, and their relatively short lifespan in the atmosphere of some of these gases means that their contribution to global climate change is dwarfed by CO2 emissions.
Aircraft also generate water vapour, another GHG that is usually omitted from discussions on climate change as it is predominantly naturally occurring.
Despite being responsible for a variety of GHG emissions, most estimates of aviation’s contribution to global warming focus largely on CO2 emissions. The International Energy Agency (IEA) did however estimate that back in 2005 commercial aviation was responsible for around 1.3% of global GHG emissions.
In terms of CO2 emissions, the IEA has also estimated that aviation is responsible for around 2.8% of global CO2 emissions. IATA and ICAO has been putting the figure at a slightly lower 2%. However, they have done that since the turn of the century, firmly ignoring industry growth.
There are a significant number of uncertainties about these estimates. It has also been suggested by many scientists that the impact of GHG emissions at high altitude is more harmful than equivalent emissions at ground level.
In addition, aviation also produces pollutants such as nitrogen oxide, carbon monoxide and sulphur dioxide which can also have damaging effects on the climate even though these are not classified as GHGs. Contrails and the resulting cirrus clouds produced by aviation, also not a GHG, are believed to be a contributing factor to increases in the temperature of the earth’s surface. Scientists estimate that when these other factors are taken into account aviation is responsible for 4.7 – 4.9% of man-made global warming.
To put what we know into context, although 1.3-2.8% of global emissions (depending on what you’re measuring and who you’re talking to) may not sound much, based on current estimates, aviation is responsible for a higher share of GHG emissions than 93% of the countries in the world. Even when its importance to global economic development is taken into account, it is clear that aviation is responsible for a disproportionate amount of climate change.
If aviation was a country, it would rank 21st in the world in terms of GDP but, based on data produced by the World Resources Institute, 14th in terms of GHG emissions. This places it just in front of the United Kingdom which is responsible for 1.2% of global GHG emissions, and incidentally is the 5th largest country in the world in terms of GDP. Meanwhile, in terms of CO2 emissions, the World Resources Institute data shows that aviation is responsible for a higher share of emissions than most countries in the world, with the exception of Germany, Japan, Russia, India, the US and China.
As we shall see in the next article, GHG emissions from aviation are expected to increase even further over the next 50 years and the industry faces a significant challenge if it is to meet any environmental obligations.
