By JANET ZIMMERMAN
11:35 PM PST on Wednesday, March 2, 2011
Wispy white jet contrails are a familiar sight, a sign of today's considerable air traffic and, to some people, a visible reminder of the environmental threat that comes with it.
The trails -- formed when moisture condenses around aircraft engine exhaust -- create cirrus clouds that block solar energy from above and trap heat below. They may be contributing to warming of the Earth's surface temperature, NASA studies show.
"There is absolutely an effect," said David Mrofka, a climate change lecturer at UC Riverside. "It's going to cool things in the daytime and warm things at night."
Numerous theories surround the trails. Scientists are studying contrails' impact on everything from climate change to crops, and conspiracy theorists contend they are the result of dangerous government experiments and cause health problems.
Contrails occur in clusters because of favorable atmospheric conditions -- temperatures below minus 40 degrees and high humidity at 30,000 feet altitude, said Andrew Carleton, a climate science professor at Penn State University in University Park, Pa. Those clusters occur over the United States, Europe and, increasingly, over Asia and Southeast Asia as air traffic grows. More than 8.3 million domestic and international flights crossed U.S. skies in 2010, according to the federal Department of Transportation. In 2003, the last year analyzed in a NASA study, there were about 27,000 flights per day over the United States that could cause contrails.
There has been an increase in contrails since the 1970s, primarily because of a change in the atmospheric pressure pattern known as the Arctic Oscillation, which influences weather in the northern, middle and high latitudes, Carleton said.
Climatologists don't know why it has changed but believe it may be related to global warming, he said.
Contrails keep daytime high temperatures lower than if the skies were clear, but they can raise the nighttime temperatures, which decreases the day-night temperature range. Changing the temperature variation near the Earth's surface could change the heating and cooling patterns and the local wind systems, which might affect evaporation rates and impact agriculture, he said.
It is hard to talk about contrails without someone mentioning "chemtrails," which some say look similar to contrails but are really chemicals sprayed secretly by the government to control the weather and climate. Some go as far as saying it is a conspiracy to reduce the population.
ON THE WEB
Norman Meek, a geography and environmental studies professor at Cal State San Bernardino, said the chemtrails conspiracy theory complicates the public's perception of the issue.
"We know contrails have an effect. The chemtrails are something in the imagination," he said. "It affects (people's) understanding because they are unsure of the two."
Rosalind Peterson, a former crop loss adjustor for the U.S. Department of Agriculture, has spent almost a decade documenting contrails.
"What's happening to us on most days is that these persistent jet contrails that are covering us over, instead of having blue sky days, are keeping us in manmade cloud cover," she said.
Peterson has amassed more than 19,000 documents on her Web sites, CaliforniaSkywatch.com and AgriculturalDefenseCoalition.org, that she says proves contrail coverage has been significant enough over the past 30 years to decrease agricultural production in the United States.
Peterson said she never uses the word "chemtrails" because it lacks scientific documentation and detracts from the real issue. But she does believe the government is involved in widespread geo-engineering -- modifications of the Earth's energy balance to reduce temperatures and counteract human-caused climate change. Those efforts are causing increased cases of asthma and other adverse health effects, she said.
Peterson has lobbied for full disclosure and public debate about any programs to alter the climate and wants changes to jet flight elevations, routes and fuels to reduce the man-made cloud cover.
Over her home in Mendocino County, in Northern California, Peterson said jets regularly crisscross the skies and make loops not related to airport traffic in San Francisco and Sacramento. She believes the planes are military, though NASA scientists and other researchers disagree.
Palm Springs environmentalist Geraldine Carpentier worries that the contrails signify something sinister.
"It's very concerning for me to know, despite everything we can do to lead healthy lives, there are programs in place that go beyond anything we can control," she said.
In her online newsletter, Palm Springs Green Scene, Carpentier publishes pictures of blue skies made hazy white by contrails.
Carpentier also refers to claims made by some residents of the San Bernardino Mountains in 2006 of weather modification experiments that left a dust cloud and yellowish residue, followed by an increase in respiratory ailments. She recently attended a local screening of the new documentary, "What in the World are They Spraying?" that accuses the government of geo-engineering to manipulate the climate and contaminating the soil and water.
"The scientists or agencies or associations or mainstream media who say that it's just conspiracy theory, that's a way to continue the silence around this and not have an open debate," she said.
'A LOT OF UNCERTAINTY'
Global air traffic contributes 2 to 3 percent of carbon dioxide emissions, the main greenhouse gas linked to global warming. A May study of computer models by the American Chemical Society forecast that carbon dioxide emissions from air traffic will likely double or triple in the next 50 years.
Possible solutions include making planes fly lower, outside the atmospheric conditions that create contrails, or make them fly around those areas, said Carleton, the Penn State professor. That would, however, increase fuel consumption and create more greenhouse gases, he said.
Carleton worked with David Travis, a geography professor at University of Wisconsin-Whitewater, on a study of the skies after the World Trade Center attacks on Sept. 11, 2001, when airline traffic was halted for three days.
In looking at daytime high temperatures and nighttime lows in that period, they found the average daily temperature range to be almost 2 degrees greater than when jets do fly. The conclusion was that the contrails block some sunlight from reaching Earth during the day and prevent heat loss at night.
Just how much warming results from contrails is under investigation by federal scientists.
In 2004, NASA researcher Patrick Minnis took a stab at quantifying the environmental effects of contrails. He isolated contrails on satellite data to calculate their effect on solar radiation, finding that overall the vapors contribute to warming.
"There's nobody out there trying to go out and do this; it just happens. They're trying to transport people or goods from one place to another, and they happen to make these clouds," he said.
Now Minnis is working on the Aviation Climate Change Research Initiative, a venture of the National Aeronautics and Space Administration and the Federal Aviation Administration to refine methods for detecting contrails and measuring their impact on climate. As of now, warming caused by aviation is estimated at 1 to 4 percent. The increase in temperature hasn't been determined.
"There's a lot of uncertainty," he said. "If it turns out to be a higher number, things might need to be done to cut back on it."