Atmospheric Oxygen Levels Falling

SYDNEY, Australia, July 19, 1999 (ENS) - As levels of the greenhouse gas carbon dioxide rise, concentrations of oxygen in our air have fallen, according to scientists at the Australian government research organisation, CSIRO, the Commonwealth Scientific Industrial Research Organisation.

"As fossil fuels burn, they generate carbon dioxide, using up oxygen in the process," explained Ray Langenfelds from CSIRO Atmospheric Research. "About half of the carbon dioxide from fossil fuels remains in the atmosphere," he says.

Scientists from CSIRO have measured the miniscule decline in oxygen that has occurred during the past 20 years, the longest period over which such an assessment has been made.

The team analysed air dating back to 1978 from CSIRO's unique archive of pristine air collected at the remote Cape Grim Baseline Air Pollution Station operated by the CSIRO and Bureau of Meteorology in northwestern Tasmania.

CSIRO's oxygen measurements have been made with technology available only recently and provide what researchers says is an important constraint on identification of the factors that are influencing growth of carbon dioxide in the atmosphere. Findings based on the decline in oxygen have just been published in the international journal, "Geophysical Research Letters."

"The changes we are measuring represent just a tiny fraction of the total amount of oxygen in our air - 20.95 percent by volume. The oxygen reduction is just 0.03 percent in the past 20 years and has no impact on our breathing," Langenfelds. "Typical oxygen fluctuations indoors or in city air would be far greater than this."


Air pollution over the city of Manchester, UK caused by burning fossil fuels. (Photo courtesy Atmospheric Research & Information Centre, Manchester Metropolitan University)
The oxygen measurements shed new light on the extent to which the world's forests and oceans share the task of absorbing half the carbon dioxide generated by burning of fossil fuels.

"While the oceans emerge as the slightly larger long-term sink, plants are clearly soaking up more carbon dioxide with time. If they weren't, levels of carbon dioxide would be far higher," says Langenfelds.

Although deforestation during the past 20 years has released vast quantities of carbon dioxide, remaining plants are taking up much of this gas. As plants photosynthesise, they produce oxygen, explaining why the oxygen decline in air has been less than expected.

Researchers speculate that plants today could be growing more rapidly than in the past due to warmer conditions, higher carbon dioxide concentrations or increased nitrogen fertilisation. Previously cleared land may be returning to forest, also absorbing carbon dioxide. graph