Planetary boundaries: Consider all consequences

Ocean acidification has impacts other than simple changes in pH, and these may need boundaries too.

In their definition of planetary boundaries that humans should not transgress for fear of “deleterious or even catastrophic consequences for large parts of the world’s inhabitants”, Rockström et al. (Nature 461, 472–475; 2009) consider ocean acidification as an essential part of the equation. This may be true whether we consider “inhabitants” to be all life or only humans, for the ocean and its resources are deeply embedded in human culture. But the authors’ suggested boundary, based on aragonite saturation — a measure of the extent to which seawater is saturated with the carbonate mineral — needs careful examination.

The term ‘ocean acidification’ has become the recognizable phrase to encompass the ensemble effects of elevated CO2 levels on marine life. Much as climate is understood to mean much more than temperature change, so too ocean acidification means more than simple changes in pH. Other consequences of warming and the great CO2 invasion of the ocean also need consideration as boundaries. All aerobic life in the sea, not just calcareous animals, will be affected to some degree by the ‘acidification’ challenge as oxygen levels fall and carbon dioxide levels rise.

Peter Brewer, Nature Reports Climate Change, 23 September 2009. Full article.

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