Air travel in the tropics causes more warming

25.6.2008   (New Scientist)

Want to salve your conscience and offset your holiday carbon emissions? You might
want to rethink that trip to the tropics. A typical flight there has a greater
impact on global warming than a flight in temperate latitudes.

As well as producing carbon dioxide and contrails, planes also produce nitrogen
oxide, which triggers both the creation of the warming gas ozone, and the destruction
of another greenhouse gas, methane (Journal of Geophysical Research, DOI: 10.1029/2007/JD009140).

In mid-latitudes, these ozone and methane reactions cancel each other out and
you get zero net warming from nitrogen oxide emissions, says Keith Shine of the
University of Reading, UK.

But the brighter sunlight in the tropics is very efficient at converting nitrogen
oxide to ozone – in fact it creates ozone five times faster than in the air of
mid-latitudes, according to Shine’s calculations – whereas methane destruction
only increases marginally. Worryingly, the warming effects of ozone are particularly
strong at a plane’s typical cruising altitude of 35,000 feet, he adds.

The research raises the question of whether future attempts to control aircraft
emissions should consider extra penalties for flights in tropical countries where
air travel is booming. India, for instance, has the fastest growing airline fleet
in the world.

For now aircraft emissions are excluded from international treaties on curbing
greenhouse gas emissions. But the European Union has plans to control aircraft
emissions from 2011.[it is actually 2012 – see article ]

From issue 2662 of New Scientist magazine, 25 June 2008, page 6