For Immediate Release:
Contact: Candace Crandall
Tel: (703) 503-5064
e-mail: Crandall@SEPP.org

NEW ANALYSIS SHOWS AIR TRAFFIC INFLUENCE ON CLIMATE, CONFOUNDING IPCC GLOBAL WARMING ESTIMATES;

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.

Figure 1 Fuel consumption as a function of latitude. For every 1 lb of fuel spent, 1.2 lb of water vapour is produced. The 10-11 km range shown is the upper troposphere.

Figure 2 NOx emissions for all 1990 aircraft traffic as a function of altitude and latitude (summed over longitude) (top panel) and as a function of latitude and longitude (summed over altitude (bottom panel).

Figure 3 Satellite and ground based temperature trends (°C/decade) as a function of latitude.