Should global warming increase ocean temperatures by just a few degrees, then it is not flooding but a huge reduction in atmospheric oxygen that would pose the greatest threat to our life on Earth.

phytoplanktonShare on Pinterest
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 phytoplankton.

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 global warming.

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.

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 world.