Scripps O2 Global Oxygen Measurements | Hacker News Reader

Scripps O2 Global Oxygen Measurements

scrippso2.ucsd.edu

While the decline in O2 doesn't present any immediate danger, it does bring up an interesting scientific question: why has the Earth's atmosphere's O2 concentration remained within a certain range during the Phanerozoic era (since the Pre-Cambrian)?

Oxygen is produced by photosynthesis, but build up of O2 in the atmosphere is governed by the balance between net O2 production due to burial of organic matter (organic matter left at the surface gets consumed and re-oxidized, causing no net increase in atmospheric O2), and exposure/oxidation of reduced materials in eroded rocks and of reduced gases from volcanoes.

There is no a priori reason why these two processes have to be in balance, and both are expected to be quite variable, affected by climate, tectonics, changes in species, and amount of erosion. Absent photosynthesis, the time scale for the latter processes to deplete the atmosphere of oxygen is only 10 million years or so. Oxidizing reduced materials (organics, but also ferrous iron, other transition elements, and sulfides) in the top 200 meters (IIRC) of the Earth's continents would consume all the atmosphere's oxygen. So, why has O2 not gone to zero (or close to it) at some point in the last 600 million years?

One might argue there's some negative feedback effect, but none has been identified. You might think fire would do it. The idea would be that at high O2 levels, fires would burn even wet wood, turning the world into a blazing inferno with less photosynthesis (never mind that this would not affect phytoplankton, which causes much of the net burial of organic matter). But during the Carboniferous, atmospheric O2 levels reached nearly twice what they are now. That was when 90% of world coal deposits were produced. And fires might even make organic burial worse -- a positive feedback -- by producing charcoal that's highly resistant to decomposition. A significant fraction of coal in Carboniferous coal deposits is in fact charcoal, thought to be from wild fires sweeping across swampy forests.

The explanation for the stability may be anthropic selection. Had O2 crashed to near zero, higher life (including vertebrates) would have been wiped out, and we would not be here. If our descendants explore the galaxy and its Earth-like planets, they might find that this long run of luck is extremely uncommon. If this is the case, then humanity is going to have to take control of O2 levels in the future, as past luck is no guarantee of future luck.

People have a lot of misconceptions about atmospheric oxygen. There is a lot of it. If every photosynthetic organism on the planet died, it would still take tens of thousands of years before we had to worry about an appreciable reduction in breathable oxygen levels. We're not going to run out of it unless literally every oxygen-producing organism on the planet dies (trees don't even matter; they could all die and we'd be fine forever). If all plants and phytoplankton die, we'll starve to death and won't have to worry about oxygen levels.

In case you're interested in dealing with the data yourself, consult https://scrippso2.ucsd.edu/osub2sub-data.html to identify CSV files, and try e.g. the following to plot a timeseries in R, and to show the results of linear and quadratic fits.

  url <- "https://scrippso2.ucsd.edu/assets/data/o2_data/o2_daily/altoav.csv"
  d <- read.csv(url, comment.char='%')
  year <- d[,7]
  O2 <- d[,3]
  plot(year, O2, type="l")
  
  # Linear fit
  m <- lm(O2~year)
  abline(m)
  summary(m)
  
  # Quadratic fit
  m2 <- lm(O2~year+I(year^2))
  lines(year, predict(m2), col=2)
  summary(m2)

Losing O2 isn't a huge deal as humans - it's the outsized effect of replacing O2 with CO2. O2 is 20% of the air, N2 is 78%.

CO2 lives in that last little bit and, given its miniscule contribution to composition, has a far outsized effect.

Losing O2 has an effect on cognition.

It's 0.002%/yr. Mostly just impressed that we can measure this at all.

Gaining CO2 has more of an effect: https://www.news-medical.net/news/20200421/Atmospheric-CO2-l...

TIL that pulse oxymeters can read over 95% in the presence of carbon monoxide poisoning.

https://pubmed.ncbi.nlm.nih.gov/8037391/

However, the point of that study is that the oxygen levels are not 95%. The pulse oxymeter is wrong, and that study is about determining how wrong it is.

The abstract basically says you can subtract the blood carbon monoxide level from the pulse oxymeter's reported blood oxygen level to find the actual blood oxygen level. (They were a bit more precise than that, but it was very nearly one-to-one.)

A pulse oxymeter measures oxygen levels indirectly. It works by checking the colour of your blood. I suppose that the colour of carbon-monoxide poisoned blood must be similar to that of oxygenated blood. Perhaps because carbon monoxide attaches to blood cells in a similar way to pure oxygen.

Right - I get it. It can read over 95% in the absence of oxygen if carboxyhemoglobin tricks it out. I thought this might explain why during the pandemic, I could get a pulse ox reading of 85%, then smoke a cigarette and make the little bastard stop beeping.

Yes this is correct. Heme binds to CO in the same way it binds to O2–the iron is oxidized and has the same color.

This is also the source of carbon monoxide toxicity, as it binds to CO tighter than O2.

Yup. Same reason cyanide is deadly. Ain't chemistry grand? Good for a smoker to know since we're carrying quite a bit more than your average jogger... https://en.wikipedia.org/wiki/Carboxyhemoglobin#Affinity_of_...

This amount? I really doubt it.

But in practical circumstances (indoor air) you will suffocate through co2 poisoning long before you would notice less o2.

"The observed downward trend amounts to 19 'per meg' per year. This corresponds to losing 19 O2 molecules out of every 1 million O2 molecules in the atmosphere each year."

That's a 0.0019% decrease, not very significant is it?

Not today, but the trend is worrying, especially if the rate increases. What will this look like in 50 years? 1,000?

50 * 0.0019% = 0.00095 1000 * 0.0019% = 1.9%

Previous commenter said if the loss accelerates. Larger and larger changes each year would be more than worrisome.

I agree, we should consider that further oxygen loss could come from long burning wild fires etc, should the environment lend itself to a higher propensity to them. This could both burn oxygen and remove plants that would therefore not create and replace oxygen (in the short terms at least).

I am sure there are some weird feedback loops we are going to see in the next century or two, that aren't yet considered an issue.

We're quite likely to start running out of fossil fuels in the next few decades. It is unlikely that the loss will accelerate.

To play devil's advocate: Nothing suggests the trend will accelerate. It is just as likely to decelerate.

am i missing something? this is right in the FAQ:

``` Should we be concerned that the atmospheric oxygen supply is declining?

This point was addressed in an article by Broecker (Science, Vol. 168, 1537-1538, 1970). Although written many years ago, the basic point made by the article remains valid. The maximum potential loss of O2 from fuel burning, when fossil fuel reserves (mostly coal) are exhausted is only a few percent of the atmospheric burden. Since even this loss will take many centuries to materialize, it's hard to see this as high on the list of possible environmental concerns. ```

The striking thing to me about this is the sensitivity of the instrument.

This is interesting because it may allow to track how much of co2 in atmosphere is due to burning stuff and how much through natural release (volcanoes, ice caps melting and so on).

Man-initiated processes usually eat up o2, natural processes don’t.

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