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Can flying ever be green?

Mark Anslow

24th July, 2008

Soaring fuel prices and stratospheric carbon emissions bode ill for the aviation industry. Is flying beyond redemption? Mark Anslow tries some blue-sky thinking

The soaring cost of crude oil works in mysterious ways: hard-up hauliers park their rigs along London’s A40, fishermen camp outside Defra with placards and motorcyclists ride noisy go-slows on the M62.

Airlines, however, are much less demonstrative. They simply go bust.

In the last days of May, the world opened
its financial pages to discover that Silverjet, the loss-making business airline with an ambition to be ‘carbon neutral’, had gone into administration. Squarely blaming the rising cost of aviation fuel, the company’s directors cleared their desks in the same manner as their counterparts at the airlines Oasis, Eos and Maxjet, all victims of the price of oil.

The episode paints one thing in extraordinary clarity – the vast amount of fuel used by the aviation industry. What this means is that airlines are at the top of two concern lists: climate change, for providing the biggest easily avoidable source of greenhouse gas emissions in most Western lives; and energy efficiency, for gobbling up refined crude oil at a rate that would make the eyes of a commodities trader water.

It’s fair to say that the industry has been trying. The fuel efficiency of airliners has increased steadily at around 1.2 per cent a year, and is continuing to rise; new tax structures mean that flying half-empty planes will soon become uneconomic, and entrepreneur Richard Branson recently flew one of his planes with one engine operating on a weak blend of biofuel.

All these incremental steps, however, welcome as they are, come in the context of an industry that in the UK grows at a rate of eight per cent every year, and which is predicted to quadruple in size between 1990 and 2050. The simple fact is that if aviation continues to grow as predicted then even with projected increases in efficiency it will use the UK’s entire allocation of carbon dioxide by 2050, if we were to accept an 80 per cent reduction target.

Over the next few pages, we examine some of the more radical ideas for making flying green. They range from the scientific to the social, the old to the new, the far-out to the logical. Only one thing is sure: aviation in 2050 won’t – because it simply can’t – look anything like it does today.

Filling up with new fuel

When Richard Branson’s Virgin Atlantic 747 flew between London and Amsterdam in February of this year with one engine running on a 20 per cent blend of biofuel made from coconuts and babassu nuts, history was made – but could it become common practice?

The big problem with using biofuels at altitude – both biodiesel and ethanol – is that they clump together and freeze at much higher temperatures than kerosene. This means that they must be blended with conventional jet fuel, making a solely biofuelled plane unlikely in the near future. In addition, because they contain less chemical energy than their fossil equivalents, more biofuel would be required to go the same distance, increasing weight and reducing efficiency.

Some quick sums show the real problems with using biofuel to displace kerosene, though. In 2005, the global civil aviation industry burned some 208 billion litres of jet fuel. Replacing just 20 per cent of this with biodiesel from oilseed rape plants would require an area of agricultural land some 436,011km², or just shy of the size of Morocco.

Of course, there are higher-yielding energy crops than rape, and the industry is keen to point towards second-generation or even algae-based biofuels, but trying to supply such vast quantities of plant-based fuel in the face of spiralling global food costs now seems highly unlikely.

So what about using hydrogen to power airliners? The first jet engines were tested using it and, if it could be made using renewable electricity by splitting water, it could be a truly green fuel.

There are two main stumbling blocks. The first is down to hydrogen’s physical properties. Since it contains only one quarter the energy of kerosene, more space is needed to store it than conventional fuel. This means larger-bodied planes and hence more drag (air resistance), which in turn leads to more fuel being burned. Proponents of the blended-wing design (see ‘New Designs’), however, argue that redesigning aircraft along their lines would allow space for the extra hydrogen, but keeping hydrogen safe and liquid (and hence compact) requires thick, strong tanks and considerable insulation. And somewhere in there we’ve got to fit some passengers.

The second problem with hydrogen is more thorny. Hydrogen’s greatest asset is that, when burned, it creates only water. At altitude, however, this great asset becomes its Achilles heel. Water vapour is the most abundant greenhouse gas, and hydrogen planes would produce nearly three times as much as today’s aircraft do. This would lead to more climate-warming contrails if the jets flew at the same level as today, and an even greater impact if the planes flew at supersonic speeds in the stratosphere. The Tyndall Centre for Climate Change Research concludes ‘it is difficult to envisage a substantial penetration of hydrogen-fuelled aircraft before 2030-2040’.

A blast from the past

In light of the huge costs and lengthy development periods of new aviation technologies, investors and the industry have increasingly begun to look at lessons from the past.

In spring 2008, market observers began to notice that sales of turboprop aircraft – propeller planes – were rising. Having been struck off manufacturers’ books just a few years ago as technological relics, demand for more fuel-efficient planes led to a sudden resurgence. Two leading plane builders in Canada and France saw their orders for turboprops rise from just 26 in 2002 to 140 this year.

Although they are both slower and noisier (for passengers) than jets, turboprops use between a quarter and a third less fuel, and offer considerably better economy on short-haul flights – one manufacturer claims a full, modern turboprop can achieve fuel efficiencies of 84 miles per gallon – better than a lone driver in a Toyota Prius, though this doesn’t take account of emissions at altitude.

Even more radically, veteran environmental campaigner George Monbiot has recently given new wind to the idea of using airships for sustainable aviation. Long-thought to have disappeared with the fiery demise of the Hindenburg in 1937, lighter-than-air technology has merely been simmering in the background, waiting for its chance to reappear.

It has some appealing statistics: the Tyndall Centre for Climate Research estimates that an airship would produce between just 10 and 20 per cent of the global warming effect of equivalent aeroplanes, with the possibility of an even bigger reduction if the craft were powered with hydrogen or solar power.

UK-based company the Advanced Technology Group has designed and modelled a 21st-century version of the airship, known as the ‘SkyCat’. Looking rather like a fat plane – with a big, swollen hull full of helium but tailfins and rudders like an aeroplane – the SkyCat team believes that the ship could transport as many as 1,500 people at a time, using as little as 30 per cent of the fuel of a conventional aircraft. The craft could travel at approximately 150kph (93mph), which means London to New York in 43 hours – not quite Concorde, but perhaps an acceptable price to pay for an 85 per cent cut in greenhouse gas emissions.

The stumbling block, though, as the company’s managing director Michael Stewart explains, is finance. ‘The economics of SkyCat are absolutely compelling,’ he says. ‘The World Food Programme would hire one from us tomorrow if we had one. Unfortunately, we need about $200 million to build the first one, and people with that kind of money tend to be pretty averse to financial risk at the moment.’

Even though the Advanced Technology Group’s SkyCat could be used for everything from eco-tourism to oil pipeline transportation – and even with oil at $140 a barrel – the idea remains, as yet, confined to a one-sixth scale model in Cardington, Bedfordshire.

The runway or the highway?

Can flying ever be green? The answer, surprisingly, is yes: under certain specific circumstances, flying can be a comparatively energy-efficient way of travelling a long distance. Distances in themselves are not the problem, however. The problem is speed.

It is often said that the advent of aviation compressed time. If one business can be on the other side of the Atlantic in six hours then anyone who is any slower will simply lose out. It is the desire for speed that has led to the extraordinary growth in short-haul flights, whereas trains or turboprop aircraft have always provided more efficient and often more comfortable solutions. It is the desire for speed that led commentators to scoff at George Monbiot’s suggestion that the airship be re-examined, even though it could transport vast quantities of freight or people, with minimal emissions. And it is the desire for speed that has led to renewed clamour for faster and faster rail services, taking trains beyond the point at which they operate efficiently and supercharging them to get our velocity fix.

The tools and designs for making aviation green are already making their way off the drawing board and into prototypes. What stops them getting further are the demands of the speed status quo. So how best to send a message to the aviation industry that we want change? Find alternative ways to travel. Don’t book short-haul flights where any alternative exists and avoid long-haul flights wherever possible. By choosing not to fly today, we spur the innovation and design of tomorrow, make the economics of cheap flights impossible and send the clearest possible message to the industry that the days of climate-wrecking 550mph travel are well and truly numbered.

Mark Anslow is the Ecologist’s senior reporter

This article first appeared in the Ecologist July 2008


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