The paper, 'Elevated CO2 increased leaf-level productivity and water use efficiency in the early Miocene,' can be obtained from the authors or media@egu.eu.
Scientist contacts:
Tammo Reichgelt tammo.reichgelt@uconn.edu
William D'Andrea dandrea@ldeo.columbia.edu
The Earth Institute, Columbia University mobilizes the sciences, education and public policy to achieve a sustainable earth. The word "sustainable" is usually just virtue signaling, so it annoys me! I'll have you know this free climate science blog is sustainable as long as I'm still breathing!
A 23-million-year-old leaf preserved in a onetime New Zealand lake bed, is a key to past atmospheric conditions. One can see veins, glands along the teeth, and holes gnawed by insects:
Leaves from a 23-million-year-old forest link high levels of atmospheric carbon dioxide with increased plant growth, and the hot climate of the time. The finding adds to the understanding of how rising CO2 affects plant life if future CO2 levels mirror those of the distant past. Never mind the thousands of scientific studies, and many decades of greenhouse owner's experience with CO2 enrichment all around the world, for already revealing that more CO2 in their air stimulates plant growth!
Scientists retrieved leaves from a unique onetime New Zealand lake bed that holds the remains of plants, algae, spiders, beetle, flies, fungi and other living things from a warm period known as the early Miocene. Geologists say CO2 levels were high then, and many plants could harvest it more efficiently for photosynthesis. The findings were published August 2020, in the journal Climate of the Past.
"The amazing thing is that these leaves are basically mummified, so we have their original chemical compositions, and can see all their fine features under a microscope," said lead author Tammo Reichgelt, an adjunct scientist at Columbia University's Lamont-Doherty Earth Observatory and assistant professor of geosciences at the University of Connecticut. "Evidence has been building that CO2 was high then, but there have been paradoxes."
The "carbon fertilization effect": Lab and field experiments have shown that when CO2 levels rise, many plants increase their rate of photosynthesis, because they can more efficiently remove carbon from the air, and conserve water while doing so. Indeed, a 2016 study based on NASA satellite data shows a "global greening" effect mainly due to rising levels of manmade CO2 over recent decades; a quarter to a half of the planet's vegetated lands have seen increases in leaf volume on trees and plants since about 1980. The effect is expected to continue as CO2 levels rise.
Most of today's plant life used for food by humans ans animals (C3 photosyntheses) evolved in a higher CO2 world, believed to average 1.000 ppm, compared with 415 ppm CO2 today.
Note that when higher CO2 levels make plants grow larger, they tend to contain more water and fiber. You may need to eat a slightly larger portion than the same plant grown with lower CO2, to get the same amount of some minerals, such as calcium, iron, and zinc and other minerals. Other nutrients will be higher in an equal portion of the vegetable. The changes are small enough to ignore, but of course climate alarmists are howling about them, as usual. They could not care less, I suppose, if there is not enough food to eat in our current, historically low CO2 world?
The deposit is located in a small, long-extinct one kilometer volcanic crater now located on a farm near the southern New Zealand city of Dunedin. The crater once held an isolated lake where successive layers of sediments built up from the surrounding environment. The feature was recognized only within about 15 years ago, and called Foulden Maar. Recognizing it as a scientific gold mine, they have been studying it ever since.
Researchers took samples from a 2009 drill core that penetrated 100 meters to near the bottom of the now-dry lake bed. Between whitish annual layers of silica-rich algae that bloomed each spring for 120,000 years are alternating blackish layers of organic matter that fell in during other seasons, including leaves from a subtropical evergreen forest.
The leaves are preserved so perfectly that scientists can see microscopic veins and stomata, the pores by which leaves take in air and concurrently release water during photosynthesis. Unlike most fossils, the leaves also retain their original chemical compositions. It is the only such known deposit in the Southern Hemisphere, and far better preserved than a few similar ones known from the north.
The Miocene average global temperatures are thought to have been 3 to 7 degrees C hotter than today, and ice largely disappeared at the poles. Yet proxies from marine organisms, don't reveal high CO2 levels. have suggested CO2 levels.
Researchers at Foulden Maar analyzed the carbon isotopes within leaves from a half-dozen tree species found at various levels in the deposit. They also analyzed the geometry of the leaves' stomata and other anatomical features, and compared these with modern leaves.
By combining all the data into a model (?), they found that atmospheric CO2 was about 450 ppm, and trees were very efficient at sucking in carbon through the stomata, without leaking much water through the same route while stomata were open. This allowed trees to grow in marginal areas that otherwise would have been too dry for forests.
Human CO2 emissions have now pushed atmospheric CO2 levels to about 415 parts per million, and they may reach 450 ppm in a few decades.
Study coauthor Daphne Lee, a paleontologist at New Zealand's University of Otago, led the charge to study Foulden Maar's rich ecosystem after it came to light. More recently, she became an unexpected defender of the maar, when a company with owners in Malaysia and the United Kingdom announced plans to strip-mine the deposit for use as a feed additive for for pigs, ducks and other farm animals. The Dunedin city council is now looking into buying the land to protect it.
The study was coauthored by Ailín del Valdivia-McCarthy, a former intern at Lamont-Doherty; Bethany Fox of the University of Huddersfield; Jennifer Bannister of the University of Otago; John Conran of the University of Adelaide; and William Lee of the University of Auckland.