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).

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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 / Permian CO2 levels but for Mesozoic / Early 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 for the transition between glaciar and interglaciar 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

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.