CO2 emissions predicted to reduce density of thermosphere by 2017

A recent study by scientists from the National Center for Atmospheric Research (NCAR) and Pennsylvania State University has revealed that carbon dioxide emissions from the burning of fossil fuels will produce a three percent reduction in the density of Earth's outermost atmosphere by 2017.

The research appears in the latest issue of the journal Geophysical Research Letters and will be presented at the American Geophysical Union conference in San Francisco, California.

"We're seeing climate change manifest itself in the upper as well as lower atmosphere. This shows the far-ranging impacts of greenhouse gas emissions," said NCAR scientist Stan Solomon, a co-author of the study.

According to Solomon, lower density in the thermosphere, which is the highest layer of the atmosphere, would reduce the drag on satellites in low Earth orbit, allowing them to stay airborne longer.

"Forecasts of upper-level air density could help NASA and other agencies plan the fuel needs and timing of satellite launches more precisely, potentially saving millions of dollars," he said.

"Recent observations by scientists tracking satellite orbits have shown that the thermosphere, which begins about 60 miles above Earth and extends up to 400 miles, is beginning to become less dense," added Robert Kerr, program director in the National Science Foundation's (NSF) Division of Atmospheric Sciences.

"At heights of more than 60 miles, one of the main elements of the atmosphere is atomic oxygen, a single atom of oxygen. As carbon dioxide increases near Earth's surface, it gradually diffuses upward and absorbs heat through collisions with atomic oxygen. It then radiates the heat away to space through infrared radiation, and the result is a net cooling of the upper atmosphere. As the molecules cool and settle, the thermosphere loses density," Kerr added.

According to researchers, the 11 year old cycle of solar activity is also affecting the density of the thermosphere.

"During the active phase of the cycle, ultraviolet light and energetic particles from the sun increase, producing a warming and expansion of the upper atmosphere. When solar activity wanes, the thermosphere settles and cools," said Solomon.

For their study, the team used a computer model of the upper atmosphere that incorporated the solar cycle as well as the gradual increase of carbon dioxide due to human activities.

The team also used a prediction for the next solar cycle, which showed a decrease in thermospheric density from 1970 to 2000 of 1.7 percent per decade, or about 5 percent overall.

Findings revealed that the decrease was about three to four times more rapid during solar minimum than solar maximum.

Researchers said since many satellites, including the International Space Station and the Hubble Space Telescope, follow a low Earth orbit at altitudes close to 300 miles, over time, the upper atmosphere drags the satellites closer to Earth.

"The amount of drag depends on the density of the thermosphere, which is why satellite planners need better predictions of how the thermosphere changes. Satellite operators noticed the solar cycle changes in density at the very beginning of the space age. We are now able to reproduce the changes using the NCAR models and extend them into the next solar cycle," said Solomon. (ANI)

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