The planet’s detergent is still hard at work

Friday 19 August*

The planet’s detergent is still hard at work

A paper to be published in the prestigious science journal, Nature, this week offers a rare piece of good news on climate change but signals that the atmosphere may be more variable than previously suspected.

The team report on a New Zealand-based study of the amount of hydroxyl radical present in the atmosphere over the past 13 years using records from clean-air sites at Baring Head, near Wellington, New Zealand, and Scott Base, Antarctica.

Hydroxyl is important for cleaning up the atmosphere, especially removing carbon monoxide (a major component of ‘smog’) and methane (a greenhouse gas). It is produced by the action of ultraviolet light on water vapour and is present in tiny quantities. ‘At any one time, it makes up less than a trillionth of the atmosphere, but without it the planet would be rapidly choked by smog,’ says Dave Lowe of New Zealand’s National Institute of Water & Atmospheric Research (NIWA).

The team has found that despite the increasing pollution and greenhouse gas emissions over the past 13 years, the overall amount of hydroxyl in the atmosphere has remained the same. ‘Some people were predicting that the amount of hydroxyl would drop on the theory that there’s more junk in the atmosphere to clean up,’ says Dave Lowe. ‘Others thought that there might be more hydroxyl because depletion of the ozone layer would mean more UV available for its formation.’

Although the new study shows that there is no long-term trend in the Southern Hemisphere, it also reveals that hydroxyl is far more variable than had been suspected. It appears that the atmosphere is subject to quite large changes but is regulating itself in some way that scientists do not yet fully understand.

For example, the team found that the Mt Pinatubo eruption in 1991 caused a temporary drop in the amount of hydroxyl nearly twice as large as previously estimated, probably caused by volcanic particles in the atmosphere cutting down UV, as well as cooling the planet. In addition, another and previously unsuspected temporary drop is linked to extensive Indonesian forest fires in 1997.

‘The fact that hydroxyl is not decreasing may be one small piece of good news in a pretty bleak scientific consensus on climate change, because it means that hydroxyl is continuing to remove some methane from the atmosphere at the same rate as previously,’ says Dave Lowe. But, he cautions, ‘hydroxyl doesn’t deal with the most important greenhouse gas, carbon dioxide, and the amount of variability we are now seeing shows that the natural chemistry of the atmosphere is quite variable. So we can’t say whether it will stay that way.’

The team worked out how much hydroxyl radical was in the atmosphere using records of carbon monoxide containing radiocarbon (14C). ‘This 14CO is produced by cosmic rays from incredibly energetic sources like massive black holes at the centres of giant galaxies, that are shot across the universe, ending up in our atmosphere where they react with nitrogen to form radiocarbon, and then 14CO. The hydroxyl radical finally turns 14CO into 14CO2 ,’ says NIWA scientist Bill Allan.

Funding for this research was received from the Foundation for Research, Science & Technology (New Zealand) and Antarctica New Zealand.

The paper’s authors are Dr Martin Manning of the Intergovernmental Panel on Climate Change Working Group 1 Support Unit, USA, and Dr Dave Lowe, Rowena Moss, Dr Greg Bodeker, and Dr Bill Allan from the National Institute of Water & Atmospheric Research (NIWA), New Zealand.

ENDS

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