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I saw a friend "like" this news article on Facebook which claims that phytoplankton would stop oxygen production:

"If the world’s oceans warmed by 6 degrees Celsius—a realistic possibility if global emissions continue unabated—the tiny plants would halt oxygen production, according to the study, which was published Tuesday in the Bulletin of Mathematical Biology."

Of course, the article writer didn't include a link to the study, or even the name of the study and Google is not forthcoming.

  1. Does a significant portion of Earth's oxygen come from phytoplankton?
  2. Are phytoplankton as temperature-sensitive as the article suggests?
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    The study was linked: link.springer.com/article/10.1007%2Fs11538-015-0126-0 . The journal seems to be credible and the article peer-reviewed.
    – Polygnome
    Jun 27, 2016 at 14:56
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    I'm strongly skeptic about the claim that "By 2100, the earth at sea level could have atmospheric oxygen levels comparable to the top of Mount Everest today". AFAIK even if all oxygen production stopped suddenly, it would take several thousands of years to completely deplete the atmospheric oxygen. So 80 years couldn't reduce the level of oxygen by something like 5+%...
    – Bakuriu
    Jun 27, 2016 at 16:24
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    @polygnome while the journal is a good one, it is a mathematical biology journal, not an environmental science journal. That means the mathematical biology may have been reviewed competently, but it doesn't mean that the reviewers were experts in the environmental side of things.
    – user18604
    Jun 27, 2016 at 17:14
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    Keep in mind that the data is VERY narrow. 1 & 2 are true, but by themselves mean very little in the global sense.
    – coteyr
    Jun 27, 2016 at 17:59
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    The earth has been substantially warmer than it currently is over geological time and didn't run out of oxygen. If the model thinks it will, it is missing something important. History beats modelling every time.
    – matt_black
    Jun 27, 2016 at 20:03

3 Answers 3

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The study in question was linked at the top of the article (http://link.springer.com/article/10.1007%2Fs11538-015-0126-0).

The full name is "Mathematical Modelling of Plankton–Oxygen Dynamics Under the Climate Change", it was written by Yadigar Sekerci and Sergei Petrovskii and published in Bulletin of Mathematical Biology December 2015, Volume 77, Issue 12, pp 2325-2353.

The journal seems to be credible, and the article seems to be peer-reviewed. So the results of the paper are likely to be quite scientific and in that sense truth. You might be able to find out more about the credibility of the journal ac Academia.SE, but since my university lists it as credible journal and offers access I'd say the journal is credible.

This, however, does not necessarily mean the article is correct. Its seems to be peer-reviewed, but not completely without controversy.

The study answers your points:

This contribution appears to be massive: It is estimated that about 70% of the Earth atmospheric oxygen is produced by the ocean phytoplankton (Harris 1986; Moss 2009).

And further

It is well known that the water temperature has a notable effect on the phytoplankton growth (Andersson et al. 1994; Eppley 1972; Raven and Geider 1988).

References:

  • Andersson A, Haecky P, Hagstrom A (1994) Effect of temperature and light on the growth of micro- nanoand pico-plankton: impact on algal succession. Mar Biol 120:511–520

  • Harris GP (1986) Phytoplankton ecology: structure, function and fluctuation. Springer, Berlin

  • Moss BR (2009) Ecology of fresh waters: man and medium, past to future. Wiley, London

  • Raven JA, Geider RJ (1988) Temperature and algal growth. New Phytol 110:441–461

These references are quite old. So I would consider these things as well-understood and credible.

So there is a definite yes to 1., this is simply true. As for 2., they are sensitive to temperature change, but how much? In the end, the study has the following conclusion:

We then considered the dynamics of the corresponding nonautonomous system where the oxygen production rate slowly changes with time to take into account the increase in the water temperature due to the climate change. We showed that a sufficiently large increase or decrease in the production rate results is a bifurcation leading to a sudden depletion of oxygen and plankton extinction.

So yes, the effect is drastic. The Figure of 6° is also given:

Even if the current state of the system is safe, a sufficiently large warming (roughly estimated as 5–6 ◦C, see Robinson 2000) would inevitably lead to an ecological disaster resulting in a complete depletion of oxygen.

So all in all, the most of the claims made in the news article are really made in that study.

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  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Jamiec ♦
    Jun 29, 2016 at 13:47
  • After investigating this source, there seem to be multiple critical issues. At current, this source seems to be entirely unreliable. Discussion here.
    – Nat
    May 11, 2017 at 21:41
  • @Nat That is still not the point. the point was if the study the article talks about exists and if the study makes those claims. Both are true. The correctness of the study was never at issue here (and Its not my field, so I can not review it for correctness anyhow).
    – Polygnome
    May 11, 2017 at 21:47
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    @Polygnome The question clearly asks about the correctness of the claims, not merely if there's a study which makes them. Also, your answer attempts to argue in support of the article's credibility (even if not strongly).
    – Nat
    May 11, 2017 at 22:10
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    @Polygnome The study is easy to find. Basic understanding of the content of the atmosphere suggests the claims related to the question are ridiculous. And a survey of textbook-level knowledge would cast considerable doubt over the claims in the paper. That there is "no other study that suggests otherwise" is a function of the fact that nobody else wants to reference such a poor study, not of its credibility.
    – matt_black
    Dec 11, 2017 at 0:33
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tl;dr- The cited study's completely unscientific, and its authors have denounced it in a new paper. Their new paper's junk, too, but at least they seem to have learned their lesson about making doomsday predictions.

The original study was

and their new study's

The new study has this to say of the original one:

Admittedly, the apocalyptic prediction of the global oxygen depletion remains hypothetical as it was made in a theoretical study based on a rather simple, albeit general, mathematical model. More research is required before this could be accepted as a well established scientific fact.

-"Regime shifts and ecological catastrophes in a model of plankton-oxygen dynamics under the climate change" (2017-07-07)

So, the original authors don't stand by this claim. They're being excessively generous in describing their prior paper as "theoretical", but at least they've conceded that it's "hypothetical".

The original study was indefensible. They literally picked vastly oversimplified equations, kinda like trying to do a large quantum mechanical model with a linear regression, and then literally guessed values for their constants based on what seemed easiest. Then, when the equations crashed, they described it as predicting doomsday.

As described in an observer's blog:

There is also the 'extreme-warmer' view, that the effects of CO2 will be so large as to 'fry the planet', leading to the extinction of humans, and perhaps all life, which is surprisingly common among the general public, despite being utterly implausible. Of course, they are encouraged in this belief by alarmist papers such as 'Mathematical Modelling of Plankton–Oxygen Dynamics Under the Climate Change' by Sekerci and Petrovskii, who apparently don’t understand that any arbitrary system of differential equations has a good chance of producing unstable behaviour, and that calling such a system a 'model of a coupled plankton–oxygen dynamics' does not make it a good model. It is very, very unlikely that life on earth would have lasted for over three billion years if the global ecosystem were really as unstable as is suggested in this paper.

-"What can global temperature data tell us?", Radford Neal's blog (2015-12-03) [backticks modified]

Regarding their new study

The new study's highlights are:

Highlights

  • A model of plankton-oxygen dynamics under the climate change is developed and studied.

  • Sustainable oxygen production is only possible within a relatively narrow parameter range.

  • The global warming can cause the oxygen production to stop.

  • The regime shift is shown to be preceded by an increased regularity in plankton spatial distribution and long term transient dynamics.

-"Regime shifts and ecological catastrophes in a model of plankton-oxygen dynamics under the climate change" (2017-07-07)

The "parameters" referred to in

Sustainable oxygen production is only possible within a relatively narrow parameter range.

are their guessed values. What this means is that they don't have real data or anything like that, but rather they're making up numbers, and most of their numbers result in the equations crashing (non-"[s]ustainable oxygen production").

So, their strategy's to keep guessing numbers 'til their equations stop crashing, the range of which constitutes the "relatively narrow parameter range".

Then, how does global warming affect that? They have no idea. In fact, any slight cooling or warming can throw off those parameters again. Alternatively, they could select parameters that're stable for extreme global warming, in which case their equations would predict that global warming is necessary to save the world.

Technical stuff

This section's to provide further explanation of the original study, and some of the content's a tad technical.

enter image description here

Fig. 1 Structure of our conceptual model describing the interactions between oxygen, phytoplankton, and zooplankton. Arrows show flows of matter through the system. Phytoplankton produces oxygen through photosynthesis during the daytime and consumes it during the night. Zooplankton feeds on phytoplankton and consumes oxygen through breathing; more details are given in the text

-"Mathematical Modelling of Plankton–Oxygen Dynamics Under the Climate Change" (2015-11-25)

This simple flow model's then described by a few differential equations as

Equations (13–15) then turn into the following:

enter image description here

-"Mathematical Modelling of Plankton–Oxygen Dynamics Under the Climate Change" (2015-11-25)

Of course, these equations are vastly too simplistic such that the results'll often be absurd. Still, the authors want the results to seem reasonable, so they do a steady-state analysis to try to get the equations to predict stability.

3.2 Oxygen–Phytoplankton–Zooplankton System: Steady States Analysis

We now proceed to the analysis of the equilibria of the full system (19–21). Obviously, the steady state values are the solutions of the following equations:

enter image description here

-"Mathematical Modelling of Plankton–Oxygen Dynamics Under the Climate Change" (2015-11-25)

Finally, after finding a few fake values that they like, they then just pick those values as-if they were real.

We fix most of the parameters at some hypothetical values as B = 1.8, σ = 0.1, c1 = 0.7, c2 = 1, c3 = 1, c4 = 1, η = 0.7, δ = 1, ν = 0.01, μ = 0.1, and h = 0.1, but vary A in a broad range.

-"Mathematical Modelling of Plankton–Oxygen Dynamics Under the Climate Change" (2015-11-25)

Anyway, since their equations usually blow up and they made-up fake values that just barely hold together, then whenever they change things a bit, the equations blow up again. And so, the authors report doomsday.

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    Since you refer to inventing numbers you could point to the paper where and what is made up by the writers. As I qualitatively understand it: ocean regions attributes (temperature, salinity) will change as climate changes and probably warmer sea surface temperatures in the tropics will limit phytoplankton, but simultaneously the polar sea ice regions are getting more suitable for phytoplankton as sea ice melts.
    – Communisty
    Dec 11, 2017 at 9:24
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    It is worth nothing that one of the original authors claimed in an interview about the first paper that the world could lose more than half its available oxygen by 2100 if the model were true. This suggests he doesn't have have much of a grasp of basic facts about the atmosphere.
    – matt_black
    Dec 11, 2017 at 11:44
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    @Communisty Added a section on at the end there to explain how they invented the numbers. You're right that it should be possible for a good researcher to construct an informed model for this sort of system; unfortunately, these particular authors didn't bother for such trivialities like actual scientific models or data.
    – Nat
    Dec 11, 2017 at 16:07
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    Meta-note: The above answer was significantly restricted because SE.Skeptics doesn't have TeX. If you like science, please consider supporting TeX!
    – Nat
    Dec 11, 2017 at 16:10
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Re your second question: 'yes' and 'sort of'

Yes. About 40% of phytoplankton populations have already been lost over the past 50 years with only a half a degree mean global temp increase. Ref: https://www.scientificamerican.com/article/phytoplankton-population/

But it's not just only about phytoplankton and temperature. Acidification, hypoxia and zooplankton also have vulnerabilities in the system. There is an interdependency between zooplankton (animal-like plankton), phytoplankton (plant-like plankton) and oxygen levels that basically falls apart at a certain point because the three interact with each other.

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    nature.com/nature/journal/v466/n7306/full/nature09268.html has some words in it, I don't think this is undeniable proof that 40% has died in the last 50 years, also I don't think there is proof they produce 50% to 85% of the oxygen. Another way of saying this is phytoplankton is responsible for some amount of oxygen production, roughly estimated at 50% (+- 35%)
    – daniel
    May 11, 2017 at 8:44
  • Also no one talked about the whales, if humans harpooned all the whales in these years then krill, the predators of phytoplankton, would have a much less restrained population eat a larger number of phyoplankton.
    – daniel
    May 11, 2017 at 9:02
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    The thing is there are more significant effects than temperature. Lack of nutrients going into the ocean matters and, ironically, more green plants on land reduce this flow by stabilising soil and stopping it being blown into the ocean to feed the plankton.
    – matt_black
    May 11, 2017 at 10:09
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    Even a layman can identify a serious problem with the claim that 40% of phytoplankton has been lost. If that, and the related fact that plankton produces a large proportion of atmospheric oxygen, are both true, why have we not seen a significant reduction in the actual level of atmospheric oxygen?
    – matt_black
    Dec 11, 2017 at 0:36

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