Eco-Journal, v.17.3 May/June 2007

Is this Aeroscraft the answer to the challenge of GHG emissions from air travel?

The Threat (or Promise?) of Air Travel

By Curt Hull, Climate Change Connection

Before you whisk off to that holiday in Mazatlan, or that conference in Vancouver, you should pause before you get on the plane. I´m not talking about threats from terrorists; I´m talking about the threat your plane ride poses to the environment. In the effort to minimize the coming changes to our climate, air travel is going to be our toughest challenge.

Air travel is harmful to the atmosphere and it is becoming a bigger percentage of our greenhouse gas contribution. It will be tough to address this issue because we really like to fly and we don´t have a viable substitute. There is no other way than the airplane to move large numbers of people, long distances, really fast (especially over water). There are other forms of transportation that can satisfy two of these requirements (such as trains and boats) but only air travel satisfies all three. The promise behind this threat is that maybe it will cause us to look at why we need to go so fast, and to ask, why not slow down?

It produces a lot of greenhouse gases
Aircraft use an incredible amount of fuel, and they burn it high up in the sky where the air is thin and the chemistry is complex and fragile. Some of the stuff emitted by aircraft heats the planet and some cools it.¹ The overall impact is a warming effect that is 1.9 times that of carbon dioxide alone.²

• Carbon Dioxide (CO2)—Air travel produces almost as much carbon dioxide per passenger kilometer as having a single occupant in a small car.³ However, instead of going to work or to the store for groceries, plane trips are hundreds or thousands of kilometers. A small car creates about 5 tonnes of CO2 a year. A plane trip to London and back generates about 1.4 tonnes of CO2,⁴ or more than three months driving—and that´s just the carbon dioxide.
• Nitrogen oxides (NOx) and Ozone—Nitrogen oxides are greenhouse gases and the NOx that planes produce also increase ozone concentrations. Increases in ozone in the upper troposphere are more effective at warming the planet than increases at lower altitudes.
• Water Vapour—Water vapour is a greenhouse gas. Most aircraft water vapour is released at lower altitudes where it´s removed by precipitation within one to two weeks but whatever is released in the stratosphere (above 10,000 metres) builds up.
• Contrails and Cirrus Clouds—Those thin trails behind high flying aircraft tend to warm the Earth´s surface, especially at night.
• Sulfate and Soot Aerosols—Soot tends to warm while sulfate tends to cool the Earth´s surface. Because aerosols influence the formation of clouds, their accumulation from aircraft plays a role in enhanced cloud formation and changes the properties of clouds.

We´re doing more of it
Air travel accounts for a rapidly growing piece of our greenhouse gas emissions. In 1992, it accounted for just 2% of total human-created (anthropogenic) carbon dioxide emissions or about 13% of CO2 from all transportation sources. The world´s air passenger traffic more than doubled from 1985 to 2000, and air cargo traffic grew even more quickly.

There was a decrease after 9/11 but it´s growing again, and making up for lost time. In 2004, Boeing and Airbus forecast that passenger air travel and air cargo would double the 2004 level before 2020. In 2006, they increased that forecast by 30%, mostly due to demand from new markets like China. This means 22,700 new passenger and freighter aircraft will be required over the next 20 years, 5,400 more than they predicted in 2004.⁵

During the coming years, we hope to be very successful in reducing our greenhouse gas emissions from every other source: coal-fired electrical generation, fossil fuel car travel, and home heating. If air travel keeps increasing and other greenhouse gas sources decrease, air travel will become a bigger and bigger part of the problem.

Why would air travel increase if the others don´t? We like to go places and we want to get there fast. Perhaps this is the toughest problem. We can convince people to drive hybrid-electric cars, ride their bike, or insulate their homes, but giving up that trip of a lifetime, the ability to manage a global business, or a visit to see loved ones is just too much to ask. Also, travel opens our eyes. We meet new people. We see new perspectives. Anyone who has travelled knows that the awareness and appreciation for another culture that comes from smelling it, tasting it, touching it—living it is far more profound than the insights gained from what you see and hear on the TV or internet. People who are concerned about the prospect of floods in Bangladesh or droughts in Africa (and hence, global warming), are often people who´ve been there.

Looking for a substitute
How else can we move lots of people quickly over long distances? What alternatives are there?

• What if we change the fuel?—Hydrogen produces no carbon dioxide but it has 1/4 the energy density of kerosene. So, the volume of the fuel is much greater, increasing the size of the vessel, and therefore the drag. Also, a plane burning hydrogen would produce 2.6 times as much water vapour as a plane flying on kerosene, and water vapour is a problem when planes fly in the stratosphere.
• High-speed magnetic-levitation (maglev) trains—The least expensive high-speed train routes in France cost about $12 million per km to build. At this rate, a line from New York to L.A. would cost $48 billion and take many years to build. Since they travel near the ground, wind resistance is relatively high and increases dramatically at high speed. A train moving at 350 kph uses almost twice the fuel per kilometer as one travelling at 225 kph⁶. At 350 kph, the train would use more fuel than an Airbus. High-speed trains would only cut carbon if they ran on electricity from renewable sources—and they won´t get you over the ocean.
• New-generation dirigibles—One such dirigible being proposed is the Aeroscraft⁷. It would not be lighter than air; only 2/3 of its weight would be lifted by helium. It would be two football fields long, fly below 3000 metres, and carry a 400-tonne payload. It would use six turbofan jet engines for takeoff and landing, have a range of several thousand miles, and would have an estimated top speed of 280 kph using hydrogen-powered electric propellers for propulsion. It would cross the continental U.S. in about 18 hours. One model is in production now and is expected to fly in 24 to 36 months. Who knows what promise or problems it holds when it actually starts to fly?

What can we do now?
The dirigible idea looks pretty exciting to me but it means we need to open our thinking beyond the vehicles themselves, to look at the requirements. Why do we need to travel so fast? People used to travel by regular trains and they had time to meet people and have romances.

Even within the realm of airplanes, the faster the plane, the more fuel it uses. Turboprop airplanes use about 60% of the fuel of current jets⁸. Supersonic aircraft use about 30% more fuel at cruising altitude than passenger jets⁹ and a lot more to get up there.

Sometimes we may not really need to travel at all. Some people take more than one air flight vacation a year. Why not one trip for a longer time—really experience the place. A lot of business travel is done more for the status and prestige of frequent flier miles than for real need. Video conferencing technology is getting better and cheaper all the time. It can be nearly as effective as meeting in person, much more efficient in time, and a lot cheaper.

Maybe the real threat of air travel is how it raises our expectations for speed and the promise is that, if we take this climate change problem seriously, we may start to ask—why not slow down and start enjoying the journey?

Notes
1. Intergovernmental Panel of Climate Change (IPCC) Special Report—Aviation and the Global Atmosphere—Summary for Policymakers, 1999
2. IPCC -2.7 has been used previously (e.g. George Monbiot, Heat) but 1.9 is now preferred
3. John C. Ryan, Over Our Heads: A Local Look at Global Climate (Seattle: Sightline, 1997), p.43
4. http://www.terrapass.com/flight/flightcalc.html
5. ATW Daily News, Airbus raises 20-year forecast more than 30% to 22,700 aircraft, Nov 23, 2006, http://www.atwonline.com/news/story.html?storyID=7161
6. Roger Kemp, Transportation Energy Consumption, Lancaster University, 2004
7. http://www.aeroscraft.com/
8. Avions de Transport Regional, The Latest Generation Turboprop: The Green Power of Tomorrow, no date.
9. http://www.aef.org.uk/downloads/Howdoesairtravelcompare.doc