How did plants adapt to $\small\sf{CO_2}$ levels past 400k years? Why won't they do it again?

Question

(Description from climate.nasa.gov: This graph, based on the comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric $\small\sf{CO_2}$ has increased since the Industrial Revolution. (Credit: Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record.))

I'm not sure where and why has all $\small\sf{CO_2}$ gone every 100.000 years and out of where has $\small\sf{CO_2}$ come?

But if $\small\sf{CO_2}$ came from burning trees or volcanoes and disappeared because plants adapted then I have this question:

Plants somehow tolerated these 100.000 year $\small\sf{CO_2}$ changes over time which is very evolutionary small time. So perhaps adaptation was just about changing plants' composition percentages which is very flexible. When some rare $\small\sf{CO_2}$ eating trees came to be more frequent. But if that's true why can't plants change their composition again to adjust for human $\small\sf{CO_2}$-emissions pace?

Answer 1

I'm not sure where and why has all CO2 gone every 100.000 years and out of where has CO2 come?

The amount of CO₂ in the atmosphere for the last 400000 years is very strongly correlated with temperature.

_{Temperature change (blue) and carbon dioxide change (red) observed in ice core records.
Image source: https://www.ncdc.noaa.gov/paleo/globalwarming/temperature-change.html.}

Glaciations currently occur at roughly one hundred thousand year intervals, driven primarily by Milankovitch cycles. So what causes the strong correlation between temperature and carbon dioxide levels? The primary reason for this marked correlation is that carbon dioxide dissolves in cold water much more readily than it does in warm water.

As a glacial period starts, the oceans gradually get colder worldwide as ice gradually spreads over the Northern Hemisphere. This enables oceans to absorb carbon dioxide from the atmosphere. Atmospheric CO₂ drop as a glaciation proceeds. The plot shows that both temperature and CO₂ levels drop rather slowly over the course of a glaciation, and then both rise rather quickly as the glaciation ends.

One reason for this is atmospheric carbon dioxide levels. The Milankovitch cycles triggers the end of a glaciation. The warming oceans cannot hold as much carbon dioxide as they could during the depths of the glaciation and release carbon dioxide to the atmosphere. This exacerbates the warming, releasing even more carbon dioxide into the atmosphere. This makes the escape from a glaciation much steeper than the entry into one (Shakun 2012). A nice graph from the cited paper:

_{Upper plot: CO₂ concentration (yellow circles), global temperature (blue), and Antarctic temperature (red).
Lower plot: Simulation results that show that Southern Hemisphere temperatures tends to lead but global temperatures tend to lag CO₂ levels.
Image source: http://www.nature.com/nature/journal/v484/n7392/fig_tab/nature10915_F2.html.}

But if CO2 came from burning trees or volcanoes and disappeared because plants adapted then I have this question:

Plants somehow tolerated these 100.000 year CO2 changes over time which is very evolutionary small time. So perhaps adaptation was just about changing plants' composition percentages which is very flexible. When some rare CO2 eating trees came to be more frequent. But if that's true why can't plants change their composition again to adjust for human CO2-emissions pace?

Your question is a bit moot since the increases in CO₂ did not come from burning trees or volcanoes and did not disappear because plants adapted.

Jeremy Shakun, et al., "Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation," Nature 484.7392 (2012): 49-54.

Answer 2

The main factors a plant consider are:

• Temperature (it is important the number of chill hours the plant receives by year).
• Luminosity (related with Milhankovic Cycles and climate of Pleistocene in general).
• Availability of soil and water (related with ice covered surface).

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The main change between Pleistocene's glaciar/interglaciar for plants is there is new surface to colonize. As ice retreives, ecological succession starts. Non soil lands and permafrost is gradualy replaced by soil, so grass, other plants, and termophyllous trees start to colonize the new environments, while Coniferous and other Perennial Plants get restricted. Palinologists find this succession is relatively quick in geological time terms, taking only some decades or centuries (Roucoux, K. H. et al, 2001).

This is true for all intereglaciars. Thermophilus taxa as Gramineae or Artemixia, and grassland in general colonize new ecological niches (Branch, N. P. et al, 2015).

This is specialy true at Holocene, where the displacement of cold taxa trees by grassland and other thermophyllous phyllums could became a prelude to Holocene's antrophologic agriculture (Hillman, C., 1996).

Pleistocene $\small\sf{CO_2}$ levels are lower at Pleistocene than at most of Earth's History, as shown in this graph:

Source: Wikipedia. From Gradstein et al.,2005

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This leads to think plants are adaptated to higger $\small\sf{CO_2}$ levels than Pleistocene has had and have. This is in fact true, $\small\sf{CO_2}$ levels are practically the lower known on Earth's History and plants have adaptated theirselves to Earth's environment with higger concentrations.

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Increasing $\small\sf{CO_2}$ levels at Cannabaceae makes them grow more. Plants are bigger and grow faster with the same amount of ligth and nutrients. Some cultivators use $\small\sf{CO_2}$ superlevels to make their indoor cultives more efficient. Photosynthesis become more efficient.

Cannabis Sativa endures until 1500 ppm., where $\small\sf{CO_2}$ become toxic:

Source: ilovegrowingmarijuana.com

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Both graphs are related. What is shown is thermophyllous plants are adapted non to Pleistocene CO2 levels but for Mesozoic / Tertiary ones. It would be interesting to know the tolerance for perennial plants and common Mesozoic ferns.

So $\small\sf{CO_2}$ has increased by human factors, but as temperature has not done it a lot yet and the Earth stays at the same point on Milhankovic Cycles, the only change that happens sensu lacto because of $\small\sf{CO_2}$ emissions on Kingdom Plantae is a bit more of efficency on photosynthesis and a bit more of landmass to colonize close to North Pole.

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Related link: Stratigraphic International Scale

Katherine H.Roucoux, Nicholas J.Shackleton, Lucia de Abreu, Joachim Schönfeld, Polychronis C.Tzedakis (2001). "Combined Marine Proxy and Pollen Analyses Reveal Rapid Iberian Vegetation Response to North Atlantic Millennial-Scale Climate Oscillations" Quaternary Research Volume 56, Issue 1, July 2001, Pages 128-132.

Nicholas P. Branch, Lionello Morandi (2015). "Late Würm and Early-Middle Holocene Environmental Change and Human Activities in the Northern Apennines, Italy". Università di Macerata, Dipartimento di Scienze della formazione, dei beni culturali e del turismo, Sezione di Beni Culturali, piazzale Bertelli 1, 62100 Macerata, Italia

Hillman, C. (1996). "The origins and spread of agriculture and pastoralism in Eurasia". UCL Press. ISBN-10 1857285379, 1857285387

Gradstein, FM, JG Ogg and AG Smith (2005) "A geologic time scale 2004", Cambridge University Press ISBN 0521786738

Answer 3

Why don't they do it again?

Plant life on earth has already begun to adapt to increases in CO2.

The following fragment of a transcription is from a talk given by Dr. William Happer of Princeton University on February 19, 2021 to the Hillsdale College National Leadership Seminar in Phoenix, Arizona.

Geophysical Research Letters Volume 40, Issue 12 p. 3031-3035 Regular Article Impact of CO2 fertilization on maximum foliage cover across the globe's warm, arid environments Randall J. Donohue,Michael L. Roderick,Tim R. McVicar,Graham D. Farquhar

This is the greening of the Earth measured from satellites. This picture shows areas of the Earth that are getting greener over the 20-year period. What you notice is that everywhere, especially in arid areas of Sahel (you can see that just south of the Sahara) it is greening dramatically. The western United States is greening, western Australia is greening, western India is greening. This is almost certainly due to CO2, and the reason this happens is that CO2 allows plants to grow where 50 years ago it was too dry. Plants are now needing less water to grow than they did 50 or 100 years before.

Let me show you another example of what more CO2 does in terms of making plants grow better.

In June 1967, Dr. Idso began his 35-year career at the U.S. Water Conservation Laboratory in Phoenix, Arizona, where he worked as a research physicist in its Environmental and Plant Dynamics Research Unit within the purview of the Agriculture Research Service’s National Program for Global Change, with responsibilities to determine the nature and degree of potential global change, to assess the likely impacts of global change on natural and agricultural ecosystems, and to develop strategies for either preventing or adapting to the potential consequences of global change, the scope of which effort was extremely broad, encompassing interrelated physical, chemical, biological, and meteorological processes, with the overall goals of minimizing water losses in agriculture, improving crop water use efficiency, and increasing the global production of food and fiber. 

This is a picture of Dr. Sherwood Idso, and it was actually an experiment done here in Phoenix back in the 1980s. This pine tree, I believe, is a Mediterranean variety, the Eldarica pine. On the left is a pine tree growing in the current CO2 level at that time, which was about 380 parts per million, and on the right are pine trees growing in higher and higher CO2 concentrations. You can see that the more CO2 the pine trees have available, the faster they grow. You can do this with almost any plant. Corn, wheat, cotton—they all grow better with more CO2. This is the so-called pollutant that you hear about in connection with the climate “emergency.”

So, let me explain the basics of why that works.

Cheng, L., Zhang, L., Wang, YP. et al. Recent increases in terrestrial carbon uptake at little cost to the water cycle. Nat Commun 8, 110 (2017). https://doi.org/10.1038/s41467-017-00114-5

Take a low-power magnifying glass and you will see the leaf is full of little holes or “stomata.” The little holes are to let carbon dioxide diffuse from the air into the moist interior of the leaf, where the leaf, using the special enzyme called rubisco, (one of the most ancient enzymes in the world and the most abundant protein), combines CO2 with a water molecule, H2O, to make sugar. The energy to run this little chemical factory within the leaf is provided by sunlight. The problem with this is the need for holes in the leaf. Not only do CO2 molecules diffuse in from the air, but H2O molecules diffuse out through the same hole and dry out the leaf. For every CO2 molecule that diffuses into the leaf there can be a hundred water molecules that diffuse out. So, the plant has an engineering dilemma: it has to have holes in its leaf to get the CO2 that it needs to live. But those same holes desiccate it; they dry it out, and the plant needs water to live. But plants are not stupid. All over the world, they are growing leaves with fewer or smaller holes in them in response to increasing concentrations of atmospheric CO2. If there is more CO2 in the air outside, leaves do not need as many holes, and they do not leak as much water either. That is why you are seeing the greening of the earth. It is from the plants themselves taking advantage of CO2 coming back to more historically normal levels.

There is a second important issue. The enzyme I mentioned, rubisco, is very ancient. It was probably invented, on the evolutionary scale, three and a half billion years ago. At that time, there was little oxygen in the air. So, rubisco was designed in a way that lets it be poisoned by oxygen. Plants today have a hard time when there is not enough CO2 in the air. When rubisco is charged with chemical energy to make sugar, but it cannot find a CO2 molecule, it grabs an oxygen molecule, O2, instead. It uses the oxygen to create hydrogen peroxide and other nasty oxidizing molecules. One reason for the antioxidants in your tea is to mitigate this problem. This mistaken use of an O2 molecule rather than a CO2 molecule is called photorespiration. Suppression of photorespiration is one reason plants grow better with more CO2. There is a special type of plant called C4 plant, which includes American corn and sugar cane, that has partially solved this problem. But as the CO2 levels increase, the old-fashioned C3 plants, without all the biochemical machinery to cope with photorespiration, out-compete C4 plants.

You can read the complete text of Dr. Happer's talk here

Answer 4

Have a look at the distribution of all carbon on earth and maybe it will tell you something. Carbonaceous rocks all created in a marine environment account for 99.95% of all carbon on earth (some 100 million billion tons). The next largest source is in fact the current oceans with approximately 0.038% of the total and finally we get to fossil fuels with 0.01%. It should be noted here that there is almost 4 times more carbon dissolved currently in ocean water than there is in all fossil fuels existing on Earth. The next source would represent non marine plants and soil at 0.002% and finally our atmosphere that currently contains.0008%. So, marine environments roughly contain 99.99% of all carbon on earth and they would have you believe that there is some sort of “delicate” balance between the atmosphere and the oceans. Let’s face it the oceans of the world are and will always be the greatest carbon sink on earth.

Answer 5

Temperature and a alkaline soil with ph level over 7,Salinity and the suns radiation is a guarantee and the dew collected every morning is all most plant life needs to survive. Co2 is not even a factor. The Earth has lost all its Co2 plenty of times and the plants thrive along with the microbes to start life over.