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
(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.))
