Flights’ global warming footprint at least twice as large as carbon footprint

Planes release chemicals other than CO2 with warming effects

Helen Coffey
Friday 05 November 2021 10:36
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The global warming footprint of flights is twice as big as their carbon footprint, according to a new study.

While air travel accounts for 2.4 per cent of global CO2 emissions annually, aviation has contributed approximately 4 per cent to human-induced global warming to date, Oxford University researchers have found.

This is due to the warming effects caused by other chemicals released during flights, including nitrogen oxides, water vapour and tiny particles, which alter the atmosphere around them.

“For aviation, looking at carbon emissions alone is insufficient due to the other emissions and chemical interactions that aeroplanes cause in the atmosphere,” said one of the study’s authors, Milan Klöwer.

“These so-called non-CO2 effects like nitrogen oxides and contrails increase the traditional carbon footprint of aviation by more than a factor of two.

“While this is in principle known, the calculation of how much warming aviation is actually responsible for – now and in the future – is new.”

He added: “If everyone could limit their flying to a minimum, a lot would already be achieved. Now we know how to operate more remotely, and I hope we don’t forget that lesson from the pandemic.”

The study also found that aviation on its current growth path will annex 6-17 per cent of the available remaining climate “budget” if we’re to limit warming to no more than 1.5-2C by 2050.

It’s estimated that only 2-4 per cent of the global population fly internationally in any given year.

However, modelling also suggested that a 2.5 per cent reduction in flight emissions each year would halt further warming impacts from aviation.

“Interestingly, if global aviation were to decline by about 2.5 per cent yr, even with no change in current fuel mix or flight practices, the impacts of the continued rise in accumulated CO2 emissions and the fall of non-CO2 climate forcers would balance each other, leading to no further increase in aviation-induced warming with immediate effect,” said the study.

The study, Quantifying aviation's contribution to global warming, was done in partnership with researchers from Manchester Metropolitan University and the NERC National Centre for Earth Observation.

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