Until the other week, I’d assumed that it was completely clear that flying (particularly long-haul, but all flying to some extent) was a really Bad Thing in terms of its contribution to climate change. I’ve not studied the climate change science in much detail, but I constantly hear from those who have that flying is a major contributor of the emissions that are causing climate change. And of course that’s a major motivation for our decsion to go to Greece by train this summer.
So I was a bit taken aback to read an article in New Scientist a couple of weeks ago, entitled Train can be worse for climate than plane. Could we really be hopping on a budget flight to get to Athens in just a few hours while saving the planet, our bank balances and our green credentials?
Here’s the abstract from the original paper the New Scientist article is based on -
Mikhail V Chester and Arpad Horvath, Environmental assessment of passenger transportation should include infrastructure and supply chains:
To appropriately mitigate environmental impacts from transportation, it is necessary for decision makers to consider the life-cycle energy use and emissions. Most current decision-making relies on analysis at the tailpipe, ignoring vehicle production, infrastructure provision, and fuel production required for support. We present results of a comprehensive life-cycle energy, greenhouse gas emissions, and selected criteria air pollutant emissions inventory for automobiles, buses, trains, and airplanes in the US, including vehicles, infrastructure, fuel production, and supply chains. We find that total life-cycle energy inputs and greenhouse gas emissions contribute an additional 63% for onroad, 155% for rail, and 31% for air systems over vehicle tailpipe operation. Inventorying criteria air pollutants shows that vehicle non-operational components often dominate total emissions. Life-cycle criteria air pollutant emissions are between 1.1 and 800 times larger than vehicle operation. Ranges in passenger occupancy can easily change the relative performance of modes.
What this seems to be saying is that you can’t just measure emissions from the “tailpipe” (as they put it) — you have to take into account the whole life cycle of the transport (building the train or plane, etc) and the infrastructure (the roads, airports, railways, etc). Fair enough, but the other analyses I’ve seen seem to be doing that as well.
Here’s an AirportWatch briefing for example: Aviation Emissions and Climate Change — An Overview. Among other startling figures they say that:
Air travel is the world’s fastest growing source of greenhouse gases like carbon dioxide, which cause climate change. Globally the world’s 16,000 commercial jet aircraft generate more than 700 million tonnes of carbon dioxide (CO2), the world’s major greenhouse gas, per year. Indeed aviation generates nearly as much CO2 annually as that from all human activities in Africa. One person flying a return trip between London and New York generates between 1.5 and 2 tonnes of CO2.
They also mention an Intergovernmental Panel on Climate Change (IPCC) report which suggests that:
- Aircraft released more than 600 million tonnes of CO2 into the atmosphere in 1990.
- Aircraft currently cause about 3.5% of global warming from all human activities.
- Aircraft greenhouse emissions will continue to rise and could contribute up to 15% of global warming from all human activities within 50 years.
Another article (from the David Suzuki Foundation) says:
Although aviation is a relatively small industry, it has a disproportionately large impact on the climate system. It presently accounts for 4 – 9% of the total climate change impact of human activity.
But at a time when we urgently need to reduce our greenhouse gas emissions, emissions from aviation continue to grow. For example, since 1990, CO2 emissions from international aviation have increased 83%. The aviation industry is expanding rapidly in part due to regulatory and taxing policies that do not reflect the true environmental costs of flying. ‘Cheap’ fares may turn out to be costly in terms of climate change…
Compared to other modes of transport, such as driving or taking the train, travelling by air has a greater climate impact per passenger kilometer, even over longer distances… It’s also the mode of freight transport that produces the most emissions.
So where does the truth lie in all of this? I asked my friend Julian (who is a climate change scientist) what was going on, and he explained that the situation is rather complex. The impact of aviation doesn’t just come from CO2 emissions, but from other greenhouse gases, such as nitrogen oxides (NOx) as well. The effect of these is also increased because they are released at high altitude. There is also water vapour in the form of contrails (the long thin clouds which form behind aircraft). Various calculations are used to take account of these factors, but as far as I can see there’s not much agreement among the experts on how to do these calculations. For example, many calculators for assessing the impact of air travel use a multiplier called the Radiative Forcing Index to take account of these non-CO2 factors — but the values of RFI they use vary quite widely. (This is all grossly simplified! If you want to read a full discussion, the Stockholm Environment Institute (SEI) has a paper on Carbon Offsetting & Air Travel which explains things very well.)
I think it’s important to bear in mind that all scientific research is produced by people with particular interests, who are attached to particular theories which they wish to defend. (It needn’t be anything as crude as being paid by the aviation industry to come up with particular figures — although of course that sort of thing does happen. I don’t know much about Chester and Horvath’s funding: it looks as though some of the money comes from Volvo.) The researchers who come to the conclusion that aviation is particularly damaging also have their interests. And those of us who read the research have interests too. I notice my immediate reaction to this research is to look for the flaws, since it doesn’t happen to back up my pet theory that air travel is a problem. I’m not so critical when I read the SEI report…
The Quaker Advices and queries has a section that I found a useful:
Do not allow the strength of your convictions to betray you into making statements or allegations that are unfair or untrue. Think it possible that you may be mistaken.
It’s important to speak truth, and to act on the basis of that truth. But the reality is that discerning the truth is far from easy! We need, I think, to keep reassessing our comfortable truths, keep thinking it possible that we may be mistaken. But we mustn’t get bogged down either in so much debate that we don’t ever get round to acting.
For the moment, I think the evidence is strong enough that air travel is a major contributor to climate change, and I’m not about to swap my interrail pass for a plane ticket.