Contrails - Research, comments and links

Contrails and Aviation-cirrus

Climate (01)   

Clouds Caused By Aircraft Exhaust May Warm The U.S. Climate

NASA scientists have found that cirrus clouds, formed by contrails from aircraft engine exhaust, are capable of increasing average surface temperatures enough to account for a warming trend in the United States that occurred between 1975 and 1994.

" This result shows the increased cirrus coverage, attributable to air traffic, could account for nearly all of the warming observed over the United States for nearly 20 years starting in 1975, but it is important to acknowledge contrails would add to and not replace any greenhouse gas effect," said Patrick Minnis, senior research scientist at NASA's Langley Research Center in Hampton, Va. The study was published April 15 in the Journal of Climate. "During the same period, warming occurred in many other areas where cirrus coverage decreased or remained steady," he added.

" This study demonstrates that human activity has a visible and significant impact on cloud cover and, therefore, on climate. It indicates that contrails should be included in climate change scenarios," Minnis said.

Minnis determined the observed one percent per decade increase in cirrus cloud cover over the United States is likely due to air traffic-induced contrails. Using published results from NASA's Goddard Institute for Space Studies (New York) general circulation model, Minnis and his colleagues estimated contrails and their resulting cirrus clouds would increase surface and lower atmospheric temperatures by 0.36 to 0.54 degrees Fahrenheit per decade. Weather service data reveal surface and lower atmospheric temperatures across North America rose by almost 0.5 degree Fahrenheit per decade between 1975 and 1994.

Minnis worked with colleagues Kirk Ayers, Rabi Palinkonda, and Dung Phan from Analytical Services and Materials, Inc., of Hampton, Va. They used 25 years of global surface observations of cirrus clouds, temperature and humidity records from the National Centers for Environmental Prediction (NCEP) reanalysis dataset. They confirmed the cirrus trends with 13 years of satellite data from NASA's International Satellite Cloud Climatology Project.

Both air traffic and cirrus coverage increased during the period of warming despite no changes in the NCEP humidity at jet cruise altitudes over the United States. By contrast, humidity at flight altitudes decreased over other land areas, such as Asia, and was accompanied by less cirrus coverage, except over Western Europe, where air traffic is very heavy.

Cirrus coverage also rose in the North Pacific and North Atlantic flight corridors. The trends in cirrus cover and warming over the United States were greatest during winter and spring, the same seasons when contrails are most frequent. These results, along with findings from earlier studies, led to the conclusion that contrails caused the increase in cirrus clouds.

"This study indicates that contrails already have substantial regional effects where air traffic is heavy, such as over the United States. As air travel continues growing in other areas, the impact could become globally significant," Minnis said.

Humidity is the amount of water vapor in the air and determines how long contrails remain in the atmosphere. Contrails that persist for an extended period of time are most likely to impact the climate.

Contrails form high in the atmosphere when the mixture of water vapor in the aircraft exhaust and the air condenses and freezes. Persisting contrails can spread into extensive cirrus clouds that tend to warm the Earth, because they reflect less sunlight than the amount of heat they trap. The balance between Earth's incoming sunlight and outgoing heat drives climate change.

NASA's Earth Science Enterprise funded this research. NASA's Earth Science Enterprise is dedicated to understanding the Earth as an integrated system and applying Earth System Science to improve prediction of climate, weather, and natural hazards using the unique vantage point of space.

For information about this research on the Internet, visit:

For information about NASA on the Internet, visit:

Associated Press
C02 Hits Record Levels, Researchers Find

Carbon dioxide, the gas largely blamed for global warming, has reached record-high levels in the atmosphere after growing at an accelerated pace in the past year, say scientists monitoring the sky from this 2-mile-high station atop a Hawaiian volcano.

Top North West academic to warn Lords inquiry: 
Climate change is a "weapon of mass destruction"
25th Feb 2004

A leading North West academic will tell a House of Lords inquiry into climate change this week that global warming is "the biggest threat to our economy in coming decades."
Professor John Whitelegg, an independent environment and transport consultant who also teaches sustainability issues at two English universities, including Liverpool John Moores, said today: "Neither the local councils, nor the British government, nor the EU are taking this seriously enough. Only this week the Pentagon has warned the US President that climate change could usher in an era of extreme storms and floods, refugee crises and resource wars. In the worst case scenario, Britain could have a Siberian climate by 2020. The climate is changing faster than we thought."

Briefly Empty Skies Offer Climate Clues


The suspension of flights after the Sept. 11 attacks has provided scientists with a rare chance to improve their analysis of how aviation affects climate.

When the air above 25,000 feet is humid, the skies are laced with drifting streaks called contrails, created as ice crystals form on the exhaust plumes of hundreds of jets. The wind and gravity disperse the narrow contrails, which form wispy cirrus clouds.

This veil-like type of cloud allows sunlight in to warm the earth and traps some of the rising heat before it can radiate into space. This effect is thought to add slightly to a warming trend that scientists say is caused by heat-trapping gases released when fossil fuels are burned. The ideal way to measure such an effect would be to look at the same piece of sky when air traffic is heavy and when it is absent, said Dr. Patrick Minnis, a senior research scientist at the National Aeronautics and Space Administration's Langley Research Center in Hampton, Va.

Atmospheric effects of aircraft emissions

Present commercial aircraft fly at altitudes of 8-13 km. The emissions from such air traffic can change the atmospheric composition:

Directly: by emitting carbon dioxide (CO2), nitrogen oxides (NOx = NO + NO2), water vapour, unburnt hydrocarbons, soot, and sulfate particles.
Indirectly: by a chemical reaction chain similar to smog-formation the greenhouse gas ozone (O3) can be formed. In this reaction chain nitrogen oxides act as a catalyst under the influence of sunlight. As a result of these chemical reations also the concentration of methane (CH4), another greenhouse gas, decreases.

These changes can have effects on climate

The Oklahoma Climatological Survey archives weather and climate data and products from the U.S.,

The Oklahoma Climatological Survey archives weather and climate data and products from the U.S., with particular attention to information related to Oklahoma. In addition, OCS develops its own products to help Oklahoma government, business, education, media, and public make educated weather-related decisions. 

The Oklahoma Climatological Survey conducts many projects. From collecting weather information to providing data and instruction for governmental and educational institutions, OCS is the busiest state climatological office in the nation.

For Immediate Release:
Contact: Candace Crandall
Tel: (703) 503-5064



Regional Warming Likely Produced by Ice Particles in Upper Troposphere

FAIRFAX, VA, JUNE 26, 1997---Global temperature data gathered by satellites over the past 18 years--the most reliable data available--have consistently shown a slight downward trend, contrary to climate model forecasts. Analyzing satellite data compiled by scientists John Christy of the University of Alabama and Roy Spencer of the NASA Marshall Space Flight Center, however, atmospheric physicist S. Fred Singer has discovered an unusual and previously unexplained regional warming trend over northern mid-latitudes (which includes Europe and the United States), where commercial airline traffic is at its maximum. In a paper just submitted for publication, Dr. Singer demonstrates that this warming has been increasing in line with the growth of air traffic--a correlation that is particularly striking over the last decade.

Unrelated to carbon dioxide emissions or any large-scale "urban heat island" effect, the mechanism, as Dr. Singer explains it, is this: burning jet fuel releases not only pollutants, such as nitrogen oxides and sulfur dioxide, but also large quantities of water vapor, approximately 1.2 pounds for every pound of fuel burned. With airliners routinely flying at altitudes above 30,000 feet, this water vapor condenses into ice particles (contrails) that fade into thin cirrus clouds. These cirrus clouds have radiative properties capable of producing a measurable warming at the Earth's surface.

In a research paper published in Meteorology & Atmospheric Physics (Vol. 38, pp. 228-239, 1988), Singer had already calculated that these thin, virtually invisible clouds could produce a surface warming; direct measurements of infra-red (heat) emissions from cirrus particles appear to support this view. Singer speculates that the same physical mechanism could also explain decreases in diurnal temperature range (the difference between high and low temperatures over a 24-hour period) that have been reported over northern mid-latitudes by Thomas Karl and colleagues at the NOAA Climate Data Center in Asheville, North Carolina.

"The UN Intergovernmental Panel on Climate Change (IPCC) never calculated the climate impact of commercial airline traffic, even though air traffic has been increasing at the rate of 5 percent per year," said Singer. "If it is confirmed that air traffic produces this regional climate affect, then IPCC predictions of future warming must be reduced substantially."

Dr. Singer, who earned his Ph.D. in physics at Princeton University, presented a preliminary version of his research paper at the Annual Meeting of the American Geophysical Union in December 1996, and later before a group of scientific specialists at the NASA Conference on the Atmospheric Effects of Aviation, March 1997. For a printed copy of this press release, with graphs from the research paper, please fax your request to The Science & Environmental Policy Project at (703) 352-7535.

Condensation trails add to Earth's insulation blanket

Global warming increasingly fueled by jet contrails
By Robert Roy Britt,

06/24/99: The condensation trails, or contrails, left by jet airplanes already cover more than 5 percent of the sky over some heavily traveled parts of the eastern United States. It's long been known that they are useful indicators of weather to come. Now, it seems, they may affect the
climate in a more long-term way.
A report released yesterday says these clouds of ice, which often drift into forms indistinguishable from naturally occurring cirrus clouds, already cause about one percent of all manmade greenhouse effects and will increase enough in the next 50 years to contribute significantly to global warming by adding to the insulating blanket of moisture and gases in Earth's atmosphere.

Fax: +49 8821 73573

Exhaust from long distance air traffic is polluting the upper troposphere and the lower stratosphere with an estimated growth rate of 3-4 % per year. In the traffic corridor across the North Atlantic about 40 % of the fuel is burned above the tropopause. From satellite images an additional contrail cloud cover of up to 2 % has been estimated for this region, but values on the order of 10 % have been suggested for regional scale corridors.

Contrails may enhance the greenhouse effect, but microphysical and optical properties as well as the size and global distribution of contrails are not adequately known for conclusive model calculations.

In this study a groundbased scanning lidar system is used to investigate the vortex regime (10-100 sec), the dispersion regime (100 - 1000 sec), and the diffusion regime of persistent contrails with respect to geometric and optical parameters.

Lidar measurements show that the geometric growth of contrails in a sufficiently humid environment is not only determined by turbulence but also by the structure of the local windfield. Horizontal growth can be dominated by windshear spreading a contrail to a band of several km width. The depolarization of the laser light backscattered from contrails changes from about 10 % in the early vortex regime to about 50 % in the dispersion/diffusion regime. This change has to be interpreted with a particle format n mechanism typical for contrails. The lidar also provides the optical depth at 532 nm in contrail cross sections. By calibrating CCD-camera images with this information the optical depth of extended areas of contrails can be determined. This techique will be used to improve existing algorithms which investigate contrails in NOAA AVHRR satellite images with respect to the detection limit and optical depth.

Contrails are Bad News