"Jet pollution: drawing a line in the sky"

Thursday, February 10, 2005

Jet pollution: drawing a line in the sky
Although cars generate more greenhouse gases, airliner exhaust has an
exaggerated effect, scientists say. Is it time to take action?
By Mark Clayton
The Christian Science Monitor 


Gazing into a clear blue Wisconsin sky, David Travis was amazed by what he
did not see: not one fluffy airliner contrail. Not that day or in the two
days that followed the 9/11 terror attacks, when commercial airliners in the
United States were grounded. 

For Dr. Travis, a climatologist at the University of Wisconsin at
Whitewater, that tragedy had a tiny silver lining. A sky without jet
contrails became a once-in-a-lifetime opportunity to see if the skinny,
man-made clouds really did affect climate, as he had long suspected.
 
Little is known about the global climate effects of airliner exhaust.
Although jets create far less greenhouse gas than power plants or
automobiles, they have an outsize impact because of where they spew it - the
delicate upper troposphere and lower stratosphere, five to seven miles up
from Earth's surface. And an expected boom in airline travel in coming years
is likely to swamp any efficiency gains from the next generation of
airliners, such as the just unveiled Airbus A380.

The result: growing scientific concern that jets may be turning the skies
into a hazier, heat-trapping place.

"Airliners are special because even though their total emissions are
relatively small, compared to other sources, they're putting their emissions
directly into the upper troposphere," says Joyce Penner, a University of
Michigan professor of atmospheric science and lead author of a landmark
report on aviation and the atmosphere. "It's a special location."

When injected together into the icy atmosphere, the mix of exhaust gases -
including water vapor, unburned hydrocarbons, particulates, sulfates,
nitrogen oxides (NOX), and carbon dioxide - produces clouds and has two to
three times the warming effect of carbon dioxide alone, Massachusetts
Institute of Technology researchers reported last year.

That finding meshes with what Travis found. Comparing ground temperature
readings during the 9/11 flight ban with those after and before it, Travis
found that those seemingly inconsequential wisps fanning out miles above the
earth were like a blanket, reducing temperature fluctuations nationwide.
 
Travis's findings heightened scientists earlier suspicions that the cirrus
clouds formed from contrails did much more than just suppress temperatures -
perhaps playing a bigger role in global climate change than many had
suspected. A key 1999 international report had cited airliner exhaust as
responsible for 3.5 percent of the climate warming shift.

By 2050, carbon-dioxide emissions from airliners are expected to grow two to
10 times the 1992 level, thanks to increasing air traffic, according to the
Intergovernmental Panel on Climate Change report co-authored byDr. Penner.
By then, aircraft emissions will have risen to 5 percent of the cause of
global warming, IPCC says.

New research suggests the problem could be even bigger. "Contrails can be
called a cause of warming and definitely need to be considered in
climate-change models," says Patrick Minnis, an atmospheric scientist at
Langley Research Center in Hampton, Va., part of the National Aeronautics
and Space Administration.

Hot under the contrail

Contrails not only can reduce temperature variations, but also increase
surface temperatures - enough to account for the entire warming trend in the
US between 1975 and 1994, according to a study Dr. Minnis published last
year. Still, he notes, additional research is needed. Just because contrails
"could account for all the warming, it's not absolutely certain they did,"
he says.

Other scientists say neither contrails nor airliner exhaust poses much of a
warming threat.

"If you're worried about the planet warming up, airplanes are not the first
place to look to reduce the impact," says Andrew Gettleman, an atmospheric
scientist at the National Center for Atmospheric Research in Boulder, Colo.
"It's a fairly small piece of the puzzle.... More than 95 percent of global
warming is caused by other things, like power plants."

Much of the concern over contrails' potential impact on climate is coming
from the European Community, which, ironically, unveiled the world's largest
airliner last month. The four-engine Airbus A380 - far larger than a Boeing
747 - carries up to 840 passengers. Not to be outdone, Boeing is ramping up
production of its twin-engine 7E7 Dreamliner, the first carbon-composite
airliner that will be lighter and burn far less fuel per passenger mile than
older airliners.

Improving fuel efficiency is one of the big environmental success stories in
aviation. Better engines, aerodynamics, and other factors have improved
airliner fuel efficiency 60 percent in the past 35 years, says Ian Waitz, a
professor of aeronautics at the Massachusetts Institute of Technology and an
authority on airliner emissions impact on the atmosphere.

Although the A380 and 7E7 will sport even more fuel-efficient engines, they
will add to an already burgeoning global fleet of some 12,000 airliners.
Airbus hopes to sell more than 700 of its megaliners; and Boeing, more than
2,500 of its Dreamliners.

"Even with a 40 to 50 percent improvement in fuel efficiency, you're faced
with a 3 to 20 factor increase in the amount of travel, so we are going to
have to have big increases in emissions with that kind of growth," says
David Greene, a coauthor of the IPCC report and scientist at the Center for
Transportation Analysis at Oak Ridge National Laboratory in Tennessee.
Because it will take decades to turn over the global fleet, pollution will
moderate only very slowly, he says.

Future contrail scenarios depend much on how much fuel is burned - and at
what altitude. One possible solution, noted by researchers in England, would
be to fly at lower, warmer altitudes. Contrails require moist yet very cold
air to form - prevalent over some regions, such as the American Midwest, or
Northern and Western Europe. By flying 6,000 feet lower, aircraft would
produce fewer contrails, a team of scientists from Manchester Metropolitan
University reported in 2003.

But flying lower in denser air would cut fuel efficiency. Burning more fuel
would increase carbon dioxide output, possibly neutralizing benefits, other
point out.

Problem with efficiency

Even today's more efficient engines have a downside. The ever higher
pressures and internal fuel-combustion temperatures that such engines
require tend to increase NOX emissions - a major ingredient in smog. Special
combustion-chamber designs and technology can reduce NOX formation. And such
"low-NOX" exhaust options have been available for one of today's most
popular engines - yet few are purchased because of the extra cost, experts
say.

Unless low-NOX engines become more popular, NOX could grow more than
fourfold over 1992 levels by 2050, IPCC forecasts.

Even so, the NOX issue is small potatoes, says Professor Waitz in an e-mail.
"We should be concerned about all potentially important environmental
impacts, but we must also recognize that aviation is a relatively small
contributor."

For others, however, contrails pose a threat of growing gradually into a
murky blanket that reduces earth's temperature swings and dims the sun - a
scenario that would hurt crops and even maple-sap harvests by helping
harmful insects survive.

"The jet-contrail problem is not really a pollution problem - it's a cloud
problem," notes Dr. Travis back in chilly Wisconsin. "We're disrupting the
natural radiation and energy balance of the planet ... trapping outgoing
radiation and blocking incoming sunshine. And that makes the world a
cloudier, warmer, less enjoyable place."

Timeline: commercial jet travel

   1952: British Overseas Aircraft Corporation (BOAC) inaugurates the first
commercial jet service with a flight from London to Johannesburg, South
Africa. The De Havilland Comet 1 could cruise at 480 miles per hour, 2-1/2
times as fast as the propeller-driven DC-3. Repeated crashes force BOAC to
suspend flights within two years.

   1956: The Soviet Union's Aeroflot begins the first regularly scheduled
and sustained passenger jet service with flights of its Tupolev Tu-104
between Moscow to Irkutsk.

   1958: Pan American flies the first Boeing 707 from New York to London
with 111 passengers, the largest number ever to board a single regularly
scheduled flight. The fare: $272 (or $1,778 today).

   1970: The jumbo jet era begins as Boeing's 747, capable of carrying more
than 400 passengers, enters commercial service with a Pan Am flight from New
York to London.

   2005: Airbus unveils a super-jumbo - a double-decker A380, able to carry
555 people - while Boeing pushes ahead with its smaller and more efficient
7E7, due in 2007.

   2008: Passenger air traffic is forecast to grow some 20 percent from
today's levels. China and Poland should see a rise of more than 50 percent.

Sources: US Centennial of Flight Commission; Aeroflot; Finfacts.com;
International Air Transport Association

On the Web:
Dr. Joyce E. Penner, University of Michigan Professor and Researcher
http://aoss.engin.umich.edu/go/?id1=10&id2=1&id3=34

Dr. David Travis, University of Wisconsin Professor and Researcher
http://www.uww.edu/npa/news_releases/story.php?id=354

Attached Photo's:

CLOUDY FUTURE: The number of cloud-producing contrails will multiply if
international air traffic grows dramatically, as expected.

BIG IMPACT: While the new Airbus A380, unveiled near Toulouse, France Jan.
18, is more fuel efficient than earlier Airbuses, it will leave exhaust
trails that scientists say contribute to global warming.

p14a.jpg

a380.jpg