Not enough O2 in the H2O?

Professor Jason Box is continuing his research into the effect on Greenland snow melt of particulates from fossil fuel burning and forest fires, and this set me wondering about how much atmospheric oxygen is being locked up by the same processes.

O2 levels have varied radically during last 600 million years:

- as corroborated by analysis of ancient gas bubbles trapped in amber.

Writing in the Guardian newspaper in 2008, Peter Tatchell said that research by Professor Robert Berner suggested “humans breathed a much more oxygen-rich air 10,000 years ago”, though I can’t track down the original statement and suspect Tatchell may have misunderstood. (A paper by Berner on oxygen in the Phanerozoic era can be read here.)

Tatchell appears to be on firmer ground voicing concerns about air quality in cities, though what’s in the air is more worrying than what’s absent, as this article from last month’s Mail Online India edition says. That said, cities that are prone to temperature inversion layers (e.g. Los Angeles, Beijing) may find that not only is smog locked in, but oxygen not replenished from the surrounding area as fast as it is being consumed.

Globally, there seems to have been a very small decline in atmospheric oxygen since 1990, according to an 18-year longitudinal study by Dr Ralph Keeling. According to a post on the Climate Emergency Institute website, the decline is even less than Keeling had expected, and it’s possible that increased CO2 is stimulating the growth of vegetation.

Certainly the self-styled “Rational Optimist” Matt Ridley claims greenery is increasing, but I am inclined to take his professional bullishness with a pinch of salt. Surface spread as seen by satellite misses the third dimension: the UN FAO estimates (2012 forest report) that forest cover has dropped by around a third in the last 10,000 years, and the loss has accelerated from an average of 360,000 hectares per year since civilization began, to 5.2 million annually over the last decade.

Which brings us back to the carbon dioxide-global warming debate. CO2 is a “greenhouse gas” but there are so many other factors affecting the Earth’s surface temperature that I don’t think anyone can say which way the thermometer is going to move. However, if the sea continues to warm up there is a danger that the level of dissolved oxygen in the oceans will be reduced. A study reported last year in Science Daily says that 15% of the seas are “dead zones” and suggests that an increase of a couple of degrees – as has happened since the end of the last Ice Age – can have significant effects. Again, industrial pollution and waste dumping exacerbate the damage.

The Tatchell article also refers to a claimed 30% drop in oceanic oxygen-producing phytoplankton in the thirty years since 1980, though this is disputed. Even if true, our gas tank will keep us going for the foreseeable future: the Earth’s atmosphere has a total mass of some 5 quadrillion (10¹⁵) tonnes, a fifth of which is oxygen. There’s so much that the CEI article concludes “even when fossil fuel reserves (mostly coal) are exhausted, the maximum potential loss in oxygen is only small (Broecker, 1970).”

Further, as this 1994 paper by Duursma and Boisson says:

Those evolutionary processes may or may not have a place for humanity in the long run, but we have plenty more pressing threats to worry about. One of which is that the health and productivity (for us) of the seas may be compromised if warming continues and subsurface oxygen is depleted.

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