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I had a related thought that maybe someone here can answer. We've been approaching peak phosphorus, where we're using up the easy sources in much the way we do with oil. Like oil, we'll likely just find other sources as scarcity raises the price. Also like oil, the used product ends up distributed in the environment.

My question is, if photosynthetic carbon capture is nutrient limited, what happens when we are adding both CO2 and phosphorus to the environment? Does everything grow better? And what's the next limiting nutrient?

That's a good question. Someone else may be more qualified, but here's a start. For one thing, the answer will be a bit be different in marine vs. terrestrial ecosystems.

Nitrogen limitation is one common one, which can apply either on land or in the oceans in different areas. We're adding quite a lot of that to the environment too though, up to a 200% increase in reactive nitrogen availability over pre-Haber-Bosch times [1]; accordingly about half the nitrogen in your body may come from the Haber-Bosch process [2].

In the ocean, there are already a good number of places that are Fe limited (Fe is needed to make chlorophyll, among other things [3]), so they'll stay that way unless we go with Fe-fertilization or increase dust input [4].

Si limitation is another possibility in the oceans -- particularly for phytoplankton that make silica tests like diatoms [5] (though as an interesting aside, a surprising number of plants need silica to make their phytoliths [6])

On land, there's plenty of Fe and Si (from soil), so if we're supplying P, N, and CO2 then we're mostly left with water or light (photon) limitation.

If all nutrients are superabundant (particularly in aqueous settings), then we end up with runaway growth and eutrophication, which is dangerous in its own way [7]

[1] https://en.wikipedia.org/wiki/Human_impact_on_the_nitrogen_c... [2] https://en.wikipedia.org/wiki/Haber_process#Economic_and_env... [3] https://www.tandfonline.com/doi/abs/10.1080/0190416840936323... [4] https://en.wikipedia.org/wiki/Iron_fertilization [5] https://www.sciencedirect.com/science/article/pii/S096706370... [6] https://en.wikipedia.org/wiki/Phytolith [7] https://en.wikipedia.org/wiki/Eutrophication

It is not "misleading" when the scientific evidence collected via NASA's satellites is that CO2 fertilization has been measurably greening the continents for decades: "From a quarter to half of Earth’s vegetated lands has shown significant greening over the last 35 years largely due to rising levels of atmospheric carbon dioxide." [1]

Anyone who studies the biology and evolution of plants, as well as the actual constraints of their growth processes, will understand why this gigantic transformation has been happening. There are similar measurements of major increases in ocean plankton over the last decades.

[1] https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fer...

That's a cool study. CO2 fertilization is a real phenomenon (with some caveats, which I pointed out some of), but I stand by the characterization that it is misleading to use this to suggest that we shouldn't be concerned about (or consider reversing) anthropogenic CO2 emissions, or to suggest that plants are maladapted and struggling without "CO2 concentrations at least 5-10x the current levels". Plants, algae, and cyanobacteria have had plenty of time to evolve carbon concentrating mechanisms [1] to help offset low atmospheric CO2.

My apologies if that isn't what you were doing.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2606764/

> since higher CO2 means plants can keep their stomata closed more [e.g. 5]

And that apparent silver lining's actually got a downside, too. Plants working hard to draw up water is a Good Thing, because that water is the only source of nitrogen and other elements needed to make proteins and vitamins.

CO2 just gets turned into carbs; it makes plants grow big and tall but less nutritious. This won't be a problem for us overfed gluttons in the West, but it is going to exacerbate malnutrition issues in poorer regions of the world.

See e.g.:

https://www.nature.com/scitable/knowledge/library/effects-of...

http://advances.sciencemag.org/content/4/5/eaaq1012

Woah, I learned something today! Nice references.

Biologist here. I have a simple question in response to your disinformation: What CO2 level is used in commercial greenhouses?

All scientific, controlled experiments with plants demonstrate conclusively that they thrive (faster growth, larger leaves, increased biomass, larger fruits, less need for water, etc.) at higher CO2 levels than what we have today and than we had before the Industrial Revolution. I encourage people who are intellectually curious and honest to look up the scientific papers on the topic and read them for themselves (you don't have to be a biologist or a geologist to understand the experiments, the parameters, or the outcomes).

GP said that CO2 was not the _limiting factor_. I took this to mean that something else is often the bottleneck, such as access to nutrient matter. Presumably in a greenhouse, more CO2 can be used because other bottlenecks are reduced.

Well said. Yes, if you provide unlimited water, N, P, and light in a greenhouse then of course CO2 becomes limiting, it's the only thing left!

Well, very high but that's not the point. The poster was saying that it was not the limiting factor in the environment, not in an artificial setting.