Condensation Traps Heat In Earth's Atmosphere

Could there be some truth to speculation -- bandied about by environmentalists for years -- that contrails from airliners could contribute to global warming?

Well, the verdict is still out on that... but in a study published Thursday in the journal Nature, scientists postulate the visible streaks of condensation from high-flying airliners could contribute to the greenhouse effect, by trapping heat in the Earth's atmosphere.

University of Reading meteorologist Nicola Stuber, the first author of the study, suggests that contrails' overall impact on climate change is similar in scope to that of carbon dioxide emissions from all aircraft over a 100-year period... about 2 to 3 percent of all human CO2 emissions.

Contrails -- like other high, thin clouds -- reflect sunlight back into space and cool the planet... but the study claims they also trap energy in Earth's atmosphere and boost the warming effect.

That warming effect is particularly evident at night, Stuber said.

"The solar cooling effect [in which contrails reflect solar rays back into space] only happens during the day, when the sun is up," she explained.

The study cites Britain's airline industry, where only one in four flights is a night flight... but those flights, scientists say, create some 60 percent of the warming attributed to contrails.

"The findings have implications beyond their pure scientific value," said Stuber. "...they could be used if policy makers decided to modify flight management systems in order to reduce the climate impact of aviation."

Others scientists, however, questioned the study's findings.

"The jury is out on the impact of contrails," said Patrick Minnis, an atmospheric scientist at NASA's Langley Research Center. "Until we can measure it properly and extensively, and model it and its interaction with cirrus clouds and contrails, we will continue to have large uncertainties about the effect of contrails."

FMI: www.met.reading.ac.uk