Increasing level of CO2 in upper Atmosphere

Increasing levels of carbon dioxide in the upper atmosphere are allowing satellites, and space junk, to stay in orbit for longer, according to a new study.

The research, reported in the journal Nature Geoscience, helps explain why the upper atmosphere has contracted, reducing orbital decay rates.

The paper's lead author Dr John Emmert from the Naval Research Laboratory in Washington DC says levels of carbon dioxide and carbon monoxide have reached 200 parts per million in the thermosphere - 100 kilometres above the Earth's surface - a third more than predicted by atmospheric models.

Current CO2 levels are just below 400 parts per million near ground level.

"We've seen a decrease in satellite drag and the suspected primary culprit for that was CO2 increases," says Emmert.

"This is the first direct evidence we have that CO2 is definitely increasing in the thermosphere, it's pretty straight forward."

In the lower atmosphere, carbon dioxide acts as an insulating blanket, preventing heat from the surface escaping.

"In the upper atmosphere, CO2 radiates thermal energy back into space, causing a net loss of heat," says Emmert. "That makes CO2 the primary cooling agent of the thermosphere."

"So the upper atmosphere shrinks, which reduces the drag on spacecraft, and it takes longer for their orbits to decay."