Global warming: depletion of oxygen far greater threat than flooding
Phytoplankton produce 70% of the Earth’s oxygen.
Image credit: University of Leicester
This was the conclusion researchers at the University of Leicester in the UK came to after using a
mathematical model to look at the effect of ocean temperature rise on oxygen production by
In a paper published in the Bulletin of Mathematical Biology, they explain how 70% of the oxygen in the Earth’s atmosphere comes from phytoplankton – photosynthesizing microscopic organisms that inhabit the sunlit, topmost layer of nearly all
our oceans and bodies of fresh water.
The rate at which phytoplankton produce oxygen varies with water temperature – which is affected by
For their study, the researchers formulated a mathematical model of the plankton-oxygen process and how
it responds to gradual ocean warming.
The model takes into account basic interactions in the plankton-oxygen process, such as oxygen production
by photosynthesis, oxygen consumed by plankton breathing and zooplankton feeding on phytoplankton.
‘Likely result in the mass mortality of animals and humans’
The model shows that a sustainable system of oxygen production is only possible in a middle range. And,
if the rate of production goes too high or too low on either side of this range, it leads to oxygen
depletion and extinction of the plankton.
It suggests that a rise of just 6 degrees Celsius in the temperature of the world’s oceans –
which some scientists predict could happen by 2100 – would be enough to wipe out the phytoplankton and
deplete atmospheric oxygen everywhere.
Such a catastrophe, note the authors, “obviously can kill most of life on Earth.”
Much of the debate surrounding global warming in the last 20 years has highlighted the global flooding
that could result from melting of Antarctic ice should ocean temperatures rise a few degrees above pre-industrialized levels.
Also, mainstream research has tended to focus on the carbon dioxide (CO2) cycle – since CO2 is
considered the main culprit behind global warming – with the consequence that few researchers have been
examining the effect on the oxygen cycle.
The new study suggests that when you look at the oxygen cycle and the important role that our oceans’
photosynthesizing microorganisms play in it, there is another – until now overlooked – possible catastrophic
consequence of global warming.
Senior author Sergei Petrovskii, a professor in applied mathematics, sums up the findings:
“About two thirds of the planet’s total atmospheric oxygen is produced by ocean phytoplankton
– and therefore cessation would result in the depletion of atmospheric oxygen on a global scale. This would
likely result in the mass mortality of animals and humans.”
News of the study coincides with the 2015 United Nations Climate Change Conference, which is being held in Paris from November 30th to December 11th. The objective of the Paris meeting is to achieve – for the first time in over 20
years of UN negotiations – a legally binding and universal agreement on climate, from all the nations of the