Richard Dennis in a guardian article Jan 09th 2020, called Australian Conservative Politicians out for being "Trolls" on climate change, in our political fracas during our climate expanded  bush-fire season. Richard Dennis is an economist with "The Australia Institute" think tank, and he asks why conservatives connected to the coal industry completely ignore all the future costs when it comes to climate change.

In particular he referred to an often used myth in justifications of climate change denial.   "CO₂ is plant food", which seems to imply to the target audience - How could you be so stupid?   Doesn't everyone know that?

Just to show, in 2019, some Australian mining notables are still deadly serious about propagating this myth. 'CO₂ is plant food': Australian group signs international declaration denying climate science.

Pushing this myth unconditionally should automatically fail any candidate at a serious biology exam.  It has been used by louder members of the climate change coal cabal in federal government, who love to bullshit on public ignorance.  There is to much ignorance about these simple definitions, helped by people falling for explanations that are too simple.  Even expert TED speakers do not bother too hard to fix the conventional loose terminology understanding of their audience.   

Science and agriculture researches show that the effects of higher CO₂ on plants, plus indirect effects from global heating, are important mechanisms that already reduce our biosphere's primary nutrition production. They will reduce the available nutrition flows throughout our biosphere food webs. High CO₂ and warming lead to less total primary energy production, and this is a major accompaniment of previous mass extinctions in earths history. It reduces the sustainable body size of all herbivorous animals. We should care about this at lot, as plants are still the ultimate source of all of our protein and nutrition needs. What we should call real food is more than the basic sugars of solar energy storage and metabolism.

In this you tube talk plant scientist Kristie Ebi presents research on the depletion of nutrition in cereal crops grown in conditions of higher CO₂. She showed higher CO₂ decreased levels of all nutrients.  CO₂ levels tested were those that are already expected to be reached in this century. Plant nutrition level reductions from our changed atmosphere have already been detected. Our grass fed cattle are finding it harder eat enough to be nourished.  In crops grown in conditions of air with extra CO₂, compared to identical controls, content of important minerals were reduced, including iron, zinc. Vitamin B1. Folate was reduced by an average of 30%.  These are essential nutrients for billions of people dependent on regular supplies of stored cereal products. Around a billion already suffer with nutrition related health problems.  Folate and Iron deficiency cause anemia, and are critical for fetal development and childhood nutrition. Vitamin B's are essential cofactors in the biochemical reactions of our energy metabolism.

Kristie is a careful and measured science experimenter and presenter.  She points out that corporations who should care are still not investing big in serious research on our declining plant nutrition, or how to overcome its effects in  billions of people, on the margins, across Africa and middle east. No one is proposing we can supply lifetime nutritional supplement tablets to every poor person already in dire states of micronutrient deficiency. Blackmores do not market to the poor.  We all may end up needing to be taking the supplements with our regular starch energy intakes. Otherwise mass micro-nutrient deficiency is going to cripple everyone's health. Zinc deficiency is already wide-spread. In Australia, with our good food availability, estimates are at 1 in 3 males, 1 in 10 females. Mild to moderate zinc deficiency is already common globally, estimated from diet to be around one third of global population.

Gas exchange, energy metabolism, and nutrition are connected, but different biological systems

CO₂ is an important gas in our atmosphere. It is the waste co-factor of living energy stores. Because it is a persistent greenhouse gas, climate stability demands stable CO₂ levels.  It is best stored as part of living bodies, and dead ones are best kept buried. Plants need to take it in by mechanisms of  total "gas exchange", through tiny stomata (holes) in  large exchange surface and energy capture areas of their leaves in land plants.  Gas exchange is plant "breathing".  We don't call our breathing "food".  When we humans breathe, through our breathing holes, we are as animals doing "gas exchange" in the large exchange surface areas in our lungs. The respiratory chemical energy exchange is done in our cells, in mitochondria, just like in the cells of plants.

We do not label our life-time dependency on oxygen, and constant production of carbon dioxide and energy, O2, as "animal food". Plants also exchange O2, and water through leaves and roots.  Plants lose water as H20 gas through their leaves.  The water flow upwards allows plants to take in food nutrients from their roots in surrounding soil. Whenever soil moisture dries up, plants have defence mechanisms that tend to shut their leaves down. Photosynthesis is a reverse chemical process to Respiration. Plants , from the microscopic kinds in our oceans, to cereal crops and trees, capture all the primary energy that runs all life on this planet. 

Ecologists call plants the "primary producers". The energy capture that runs every large living thing in the bisophere is captured in the sub-cellular organelles called chloroplasts inside plant cells. Oxygen, Carbon, and also Hydrogen from Water molecules, are being recycled all the time, by plants and animals. The energy flow of captured photons from our sun is all one way, through these living thermodynamic system processes. CO₂ isn't food as much as it is an exchanged and recycled co-factor in the making and breaking of structure and energy storage molecules used by nearly all life, particularly glucose. The energy is stored in the carbon rings and chains of organic chemicals, and side   attachments of their molecules, and re-released when they are broken. Plants also perform the respiration process, using the stored energy for their cellular processes of life, in similar kinds of cell organelles to us, mitochondria.

Like the plants our biological systems distinguish between "energy" food, and "nutrition" food. Higher levels of CO₂ alter these systems in very different ways. Energy flow and plant energy storage is determined by solar energy energy exposure and amounts of water available in soils.  Lower pre-industrial levels of CO₂ in air have never been a limiting factor in our ability to feed our civilisation for several thousands of years. Maybe plants grew as more nutritious back then. 

Global warming to levels that current policies allow for, drastically reduce biosphere carrying capacity.

In the video above, you have to admire an intrepid researcher that spent 15 seasons wandering around with a spade looking for fossil leaves in rock layers from the PETM in US state of Wyoming before he was able to find some.

It is unfortunate for the rest of us, that CO₂ levels of today are already making nutrition from plants more like eating junk food. With continuation of our denial bullshit, by this century's end will be our end, and we will have reached 4 degrees of global heating, based on current climate policies. We will have reached the CO₂ global heating levels of 56 million years ago, labelled as the PETM - The Paleocene–Eocene Thermal Maximum.  Only we will have caused a more than 100 times faster rate of onset. Fossil and climate evidence is at that time, CO₂ was high, and climates at the poles were tropical, with large alligator types swimming around in Arctic regions. 

The equatorial land regions were likely very hot deserts. Regions in middle latitudes had warm winters. Plant species had migrated pole-wards or disappeared. Fossils leaves buried in these times long ago, show they were like junk food - very non-nutritious. During this hot stuffy time, lots of mammal species had become reduced size versions of their kinds. Ancestors of today's horse species had shrunk from pre-warming sizes by half down to the size of small dogs. Plant eating insects had to chew off more leaves. All animals where having to process more plant growth to get sufficient amounts of essential nutrients other than energy. By simple analogy,  with our current and future global heating, Vegans will be already having eat more greens and fruit every day, and our meat animals will adapt to be reduced in size and number. Our sellers of industrial processed foods are already adapting us to future low nutrition intakes. Our bodies iand brains in future may become more hobbit-sized.

During the PETM with its long period of warm oceans, the food webs were impoverished, and supported less life, because microscopic plankton numbers decline with lower dissolved oxygen. Another problem with gas exchange again. Globally reduced nutrition base means a much reduced biosphere carrying capacity. Less food for every species, and this alone makes global mass species extinction becomes more likely. This is looking at best scenarios, ignoring the many possibilities of crop loss disasters from climate extremes, fires, plant pests and diseases.

Global high CO₂ levels, induced global heating, species migrations, and reduction of biosphere primary energy production, show that it isn't just the climate that is changing.  The entire Gaia systems are cycles and flow exchanges of energy, gases and nutrients, enabled by species physiology,  biochemistry and nutrition flows. Life systems are fully integrated into global gas exchange systems, temperatures and climates. Climate systems cannot change without drastically changing the life systems.

The crude picture of progressive warming shows as temperatures rise, whole ecosystems must move towards the poles, away from hot killing zones around the equator. For some cold adapted species there will be no place left to go to.  The available land surface area progressively diminishes with higher latitudes, so the number and variety of species must mix, and diminish as these heat refugees are squashed together. Plant growth is luxurious where fresh water access and rainfall permits, but the poor quality of the CO2 stimulated overgrowth supports fewer and smaller animal species. I suppose this might be considered a beneficial life system adaption to high CO2 global heating, as more CO2 can be buried as plant material, if it doesn't get dry and burned,rather than get consumed and returned to the atmosphere as CO2 by animals.

Finally summing up her mission to warn us, Krisie Ebi said in the lecture, "If you think that education is expensive, try ignorance". Climate ignorance is mainline Australian government policy, and this is becoming very expensive.

Link to a meta study : Effect of environmental changes on vegetable and legume yields and nutritional quality

-- https://www.pnas.org/content/115/26/6804