solutions > Transportation >
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?
top of page
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 chemicals 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)
The key greenhouse gases and materials emitted by aircraft are
Carbon dioxide (CO2)
Air travel produces almost as much carbon dioxide per passenger per 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 3 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 vapor is a greenhouse gas. Most aircraft water vapour is released at lower altitudes where it’s removed by precipitation within 1 to 2 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.
top of page
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.
top of page
How else can we move lots of people quickly over long distances?
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. 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 LA 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 225 kph (6). At 350 kph, the train would use more fuel than an Airbus.
High speed trains would really only cut carbon if they ran on electricity from renewable sources – and they won’t get you over the ocean.
Airships are free-flying buoyant aircraft that can be propelled and steered. They get their buoyancy in bags filled with gases that are lighter than air - helium or hydrogen.
One such airship being proposed is the Aeroscraft (7). 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. It would if it were real.
In June 2010, Northrup Grumman won a
half billion dollar, five-year contract to build three combat airships for the U.S. military. These Long Endurance Multi-Intelligence Vehicles (LEMV) will be bigger, higher-flying, and further-seeing than current blimps. The LEMVs will float at 20,000 feet for up to three weeks at a time, spying on everything below with a variety of sensors.
A Winnipeg-based consortium called ISO Polar is a not-for-profit airship research institute that undertakes economic and engineering studies into airship use. There is much interest in airships as a way to freight material to remote parts of northern Canada and reduce our reliance on winter roads.
top of page
The dirigible 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 jets. (8) Supersonic aircraft use about 30% more fuel at cruising altitude than passenger jets (9) 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 of 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 expectation 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?