Burn more fuel to stop air travel cooking the planet

By David Fickling

Airlines aren’t always the best allies in the fight against climate change. But one place where they’re world leaders is in their fanatical drive to burn less petroleum.

Jet fuel typically comprises about a quarter of costs for most carriers. Anything that enables them to consume less of it raises profits and enhances their ability to outcompete rivals in the cutthroat battle to fill planes with passengers.

The efficiencies this has generated over the decades are genuinely astonishing. Modern aircraft can transport passengers twice the distance for the same fuel burn as planes in 1960.

Line up a fully laden Airbus SE A320neo or Boeing Co. 787 against an efficient hybrid car like Toyota Motor Corp.’s Prius with only one or two people in it, and in most cases the fuel consumption and carbon emissions per passenger, per kilometer are lower in the skies.

To tackle one of flying’s most insidious contributions to global warming, however, airlines may have to get more comfortable burning more kerosene.

That’s because the biggest way that aircraft engines are heating the planet comes not from the carbon dioxide they emit, but from the contrails that form as they fly.

Anyone who has stared at the sky near an airport would have seen the tracks of puffy white cloud that about 15 per cent of flights draw behind themselves. They’re most often created when planes fly through cold, humid regions of clear sky where water vapor is just on the verge of freezing.

Soot emitted from the engines provides the seed around which ice crystals can grow, creating a high-altitude cloud that in turn acts as a blanket preventing heat from escaping the Earth.

They might seem innocent, but those human-made cirrus clouds are responsible for more than half of the climate damage from aviation, and 2 per cent of all the warming that humans are causing.

What’s more, 80 per cent of them are caused by about one in 50 flights passing through so-called “ice supersaturated regions” or ISSRs, pockets of the sky particularly prone to contrail formation.

If we could forecast where those areas are and route aircraft to fly under, over or around them, we might occasionally burn a little more jet fuel — but we would vastly reduce the climate impact of aviation.

Little fluffy clouds

Predicting the location of ISSRs is challenging because they’re still not well understood, but a major part of fixing that problem is a matter of data collection.

Fix humidity sensors to a tiny proportion of civil aircraft, and you would immediately have hundreds of observation platforms to help build a picture of ISSR formation in exactly the regions where planes are flying.

A government program to fly weather balloons into areas more distant from flight paths would help build a more comprehensive picture of the role of ISSRs in the climate system more generally.

Once we’ve improved the understanding of ISSRs, the next challenge is to actually get airlines to avoid them. Again, governments have a lot of ability to influence outcomes.

After jet fuel and wages, the biggest expense for most airlines is the route navigation and landing services they have to pay to (typically state-owned) air traffic control agencies and airports.

ISSRs are most likely to form over temperate regions of the Northern Hemisphere such as the US, Europe and to a lesser extent north Asia. The three areas have busy skies and well-run aviation regulators who can force aircraft to divert around ISSR pockets if they want to avoid paying a climate penalty.

Airlines might not like having to risk that cost, but it’s likely to be vastly cheaper (and more beneficial, in climate terms) than the mandates to buy sustainable aviation fuel that aircraft landing at European Union airports will start paying from next year.

At present, contrails are a classic example of a climate externality, something that no one fixes, because no one is forced to pay money to deal with them. That doesn’t need to be the case. Airspace is already an extremely heavily regulated part of the planet.

If airlines faced costs as well as benefits from flying the short route through an ISSR, they’d do their best to avoid them. Aerospace manufacturers might also find innovative solutions to reduce contrail formation, much as they’ve managed to reduce the amount of air fuel that their engines use over the decades.

No single solution is going to solve the problem of airlines’ climate impact, especially not as rising incomes lead to a general increase in air travel. It’s precisely because of the multi-pronged nature of the problem that we need to take contrails seriously.

By plucking such low-hanging fruit, we’ll buy ourselves time to tackle the far trickier conundrum of carbon emissions from planes, before it gets out of control.