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Are car emissions more important than aircraft emissions ?

March 20, 2009

In response to publicity about the climatic impacts of aircraft emissions, it has been said by, among others, Michael O’Leary of Ryanair that we should target road, not air traffic, as its emissions are much greater. Here we look the facts about the emissions and see if such claims are justified.

The government publishes annual figures of the total carbon dioxide (CO2) emissions from the UK, broken down into sectors. The statistics are available on the web (but note that this location may change as responsibility for these statistics has passed from DEFRA to DECC, Department for Energy and Climate Change). 

The last year for which statistics are available is 2007. But in order to see trends it is useful to also look at historical figures. As the baseline for CO2 emissions is often taken as 1990, this provides a good starting point for examining trends in emissions.

Key figures are shown in the table below. (Emissions are in million tonnes of CO2)


CO2 in 1990  CO2 in 2007    Growth 1990 to 2007   Annual growth 
Road    109.7  121.6  + 11 %  + 0.6 %
Air     22.7  41.4  + 83 %  + 3.6%
Total UK   624.4  584.8  – 6%  
% road  17.5 %  20.8 %    
% air  3.6 %  7.6 %    


It can be seen that at present, road traffic produces almost 3 times as much CO2 as aircraft. So the aviation lobbyists might have point …


A. The figures show that aviation emissions are growing very rapidly (3.6% pa) – far faster than road emissions (0.6% pa).

B. Aviation’s climate impacts are not confined to CO2. Water vapour and nitrogen oxides (NOx) emitted at altitude are also greenhouse gases. The government applies factor of 1.9 to CO2 emissions to reflect the climate impacts of aviation.


If these two factors are taken into account, a rather different picture emerges. If the present growth rates continue, aviation’s impacts will exceed road traffic’s in under 20 years.

Clearly, both road and aircraft emissions need to be tackled. But it is also clear that the aviation is a big and growing issue and needs to be tackled now. Trying to divert attention to roads will not do.