Acclimation and Heat Stress of Plants, and Future Crop Failures

A field of sweet corn, Flat Rock, Indiana. Photo: Jeffrey St. Clair.

One of the most popular ideas that springs into people’s minds when mulling over remedies for slowing the advance of climate change because of the ever increasing accumulation of carbon dioxide in the atmosphere, is to plant more trees, bushes and grasses. Let a greater quantity of plant photosynthesis filter our atmosphere of excess CO2.

This is not an entirely bad idea — especially in its more nuanced formulation as multi-crop regenerative agriculture coupled with wildland, wetland and forest conservation and reforestation, ending industrialized chemical pesticide monoculture farming and drastically reducing the entire meat industry, along with a popular shift to plant-based diets — though it is an entirely inadequate tactic for absorbing the ever increasing load of CO2 in the atmosphere being fed by gargantuan torrents of anthropogenic CO2 emissions exhausted as waste products from the fossil fueled engines powering today’s capitalism and militarism, which remain requirements by our capitalists and militarists for the continuation of our present civilizational paradigm.

So, planting trees is being done and will continue because it is something that many people can do to try to help, and because it poses no real threats to capitalism or militarism. But one of the cruelties of global warming is that high concentrations of CO2 combined with elevated global temperatures reduce the rate of photosynthesis and plant growth. These effects are called “acclimation” and “heat stress” of plants, respectively (

Acclimation is either an enhancing or inhibiting effect on photosynthesis by high CO2 concentrations. Generally, photosynthesis is enhanced as CO2 concentration is increased from a low level. Then above an elevated threshold concentration, the rate of photosynthesis saturates and can even be reduced. The mechanism of the effect is involved and has been the subject of research for many years by agricultural scientists interested in maximizing crop yields (for example in greenhouses).

Elevated temperatures can cause heat stress in growing plants by dehydrating them: as in their fatally drying out in a drought. However, a growth inhibiting (and even growth killing) heat stress can also occur to well-watered plants by the high temperature “denaturing” of the enzymes that control the reaction rates (the chemical reactions) of the photosynthesis process within plant leaves.

Current research on plant growth under the combined effects of elevated temperature and high CO2 concentration shows that “in heat-stressed plants at normal or warmer growth temperatures, high CO2 may often decrease, or not benefit as expected, tolerance of photosynthesis to acute heat stress. Therefore, interactive effects of elevated CO2 and warmer growth temperatures on acute heat tolerance may contribute to future changes in plant productivity, distribution, and diversity.” (

There are now scientific projections of crop yield reductions for several agricultural regions, due to anticipated rises of CO2 concentrations and their related elevated regional temperatures. A report issued by Chatham House ( on 14 September 2021 describes the following:

“The planet could be struck by a wave of ‘unprecedented’ crop failures in the next 20 years if global greenhouse gas emissions continue as usual… researchers detailed a litany of risks that climate change could pose to [food security]… global agriculture will need to produce nearly 50 percent more food by 2050 to feed a growing population. But as global demand increases, crop yields could drop by 30 percent as farmers contend with a hotter and more volatile planet… By 2050, an anticipated 40 percent of the planet’s cropland will be exposed to severe drought for at least three months per year, and the breadbaskets of the United States and southern Russia could be among the regions most affected. Europe, the report said, is likely to experience the largest increase in agricultural drought, ‘with the central estimate indicating that nearly half the cropland area will experience severe periods of drought by 2050’… By the 2040s, the United States, China, Brazil and Argentina, which grow 87 percent of the world’s maize, could suffer a steep drop in their maize production — all at the same time. ‘The probability of a synchronous crop failure of this order during the decade of the 2040s is just less than 50 percent.’… Farmers will also have to contend with a decline in the length of crop seasons and long stretches of water scarcity… East and South Asia will be particularly hard hit, with 230 million people subjected to prolonged drought by 2040. Outside of Asia, Africa will likely have the greatest number of people facing drought, exceeding 180 million by 2050. Many regions also will have to manage coastal and river flooding. By 2100… 75 million people in East, South, and Southeast Asia will face coastal flooding every year. ‘Across these three regions around 11 times more people will be impacted by coastal flooding than under a scenario in which climate change is averted.’” (

This all leads to a bleak vision of our planet’s future, where lives are shorter, food is more scarce, and 3.9 billion people “are likely to experience major heat waves.”

My purpose in describing all this is not to feed into more self-indulgent wallowing in depression and flaccid fatalism over the anticipated ‘collapse of civilization’ and ‘human extinction,’ but to show how elevated CO2 concentrations along with elevated global-regional temperatures will physically reduce our food security — crop yields — and in that way very directly shorten human life globally. This is intended to prod the public mind to get on with the job of effectively responding to global warming climate change, by cutting through the many excuses for continuing to cling to the dysfunctional behaviors (fossil fueled capitalism and militarism) driving the planetary crisis, and to change those behaviors to ensure we all have sufficient good food and clean water in an enduring future.

[Thanks to Peter Carter for pointing me to the Chatham House report.]


Notes on Carbon Dioxide in Global Warming, Acidified Oceans, and Weathered Rocks

Notes on Carbon Dioxide in Global Warming, Acidified Oceans, and Weathered Rocks

Like CO2 (carbon dioxide), H2O (water vapor) is a strongly heteropolar molecule — having one end with a positive electrical charge, and another end with a negative electrical charge — and absorbs outgoing Infrared Radiation (IR) from Earth’s surface, thus capturing heat in the atmosphere. Homopolar molecules like N2 (nitrogen) and O2 (oxygen) are transparent to IR. Inelastic molecular collisions redistribute that heat (as kinetic energy) to other atmospheric molecules (N2, O2, mainly) and atoms (Ar, He, trace components).

Most of Earth’s surface heat eventually diffuses into the oceans. Heat flows along the heat gradient in the negative direction from warmer air to colder water. The heat capacity (storage ability) of the oceans is IMMENSE (this is where ‘global warming’ ends up), and their heat content takes centuries to diffuse into a stable stratified distribution, rearranged by thermo-haline currents (a solar forcing effect) and by geometry (oceans as a spherical shell with warm equator and cold poles, so ocean heat diffuses poleward).

The fundamental problem of global warming is the ‘excess’ capture of outgoing IR (infrared radiation), reducing the rejection of Earth heat (originally delivered by incoming LIGHT radiation) into space: causing an imbalance between incoming energy (in the form of light to which atmospheric molecules are almost completely transparent) and outgoing energy (IR, to which heteropolar molecules, like CO2, H2O, CH4, NOx, are all quite opaque — absorbing).

Water vapor is by far the ‘greenhouse gas’ (IR absorber) with the highest concentration in the atmosphere at any time (immensely larger than that of CO2). It has been found by a combination of climate modeling calculations coordinated with field measurements in many global environments, that though the whiteness of clouds reflects sunlight back toward space (a global cooling effect), their IR absorptivity overwhelms that cooling, so that water vapor has a net global warming effect. As the average global temperature increases there is more water vapor in the atmosphere and this mode for global warming grows in magnitude — this is a self-amplifying or positive feedback effect.

CH4 (methane) and NOx are ‘short lived’ because they are eventually oxidized (by O, OH, formed by UV breaking up O2 and H20, and by other chemical reactions), whereas CO2 is very long lived because it is an endpoint product/species of chemical reaction chains that oxidize carbon compounds in oxygen-containing mixtures. CO2 has a low “chemical potential” and is known as a “chemical thermodynamic sink”. CH4 is eventually converted to CO2 and H2O. NOx is eventually converted to HNO3, nitric acid, which attaches itself to water droplets, so it has an aqueous form and rains out.

The long-term ‘chemical sink’ nature of CO2 is why science focuses on it as the leading culprit in the long-term trends of global warming. With greater warming of the ocean surface, more H2O vapor rises and releases its latent heat when it condenses into droplets (liquid) and ice crystals, and that ‘extra’ heat adds power to storms (winds, hurricanes: mass motion), and ultimately that ‘extra’ heat energy finds its way back into the oceans (for the portion of atmospheric heat that does not escape as IR into space).

When analyzing global warming, it all comes back to CO2. I highly recommend the book ‘Thermodynamics’ by Enrico Fermi (available in a budget-priced Dover edition): a slim volume that is a classic on the topic of chemical thermodynamics, and one of the best books on science of any kind that I have ever read.

My highly detailed outline of the chemical thermodynamics of atmospheric global warming is ‘Closing The Cycle: Energy and Climate Change’ at

The process of capturing atmospheric CO2 with rocks on the ground is one of rock weathering. CO2 in the air that brushes against the surface of carbonate and silicate rocks has a finite (and very low) probability of undergoing a chemical reaction with the rock surface, fixing the airborne CO2 onto a solid substrate. This is the longest term natural process of capturing CO2 from the atmosphere (10s to 100s of millennia).

A shorter term process is capture by the surface waters of the oceans, and that aqueous CO2 then combining with water molecules and already existing carbonate ions (CO3-2) in the water to form carbonic acid (H2CO3), which is weakly bound and both acidifies the oceans and scarfs up free floating carbonate ions to both starve mollusks, corals and foraminifera of the easiest chemical species from which to grow their shells (CO3-2), and even dissolving such shells of existing organisms (most being part of the masses of plankton, the base of the oceanic food chain).

The surface (not too deep) load of absorbed acidifying CO2 is then slowly cycled to the ocean floor by the ~1,000 year vertical currents, and at the bottom it dissolves the chalk deposited as the calcium carbonate (CaCO3) remnants of dead sea life, basically bone, shell and foraminifera casing ‘fossils’ — an ocean acidifying effect. So ocean capture of CO2 happens all the time, but the intake rate can saturate as the ocean becomes more acidified; eventually this intake process could shut off, coral reefs being a long lost memory by then.

Loss of “excess” ocean CO2 requires a low CO2 concentration atmosphere that can accept the gaseous release (is not saturated with CO2) of ocean CO2 that slowly diffuses out on mainly kilo-year timescales. A technically accurate description of ‘the carbonate system in seawater’ is given at My more formal article than the discussion here, ‘Global Warming and Ocean Acidification Accelerate,’ is at

The next quicker process of fixing atmospheric CO2 is photosynthesis, and this is done both by plants on land and in the oceans, like: seaweed, giant kelp, and many small plankton-sized organisms; ocean based photosynthesis is a huge component. This happens all the time and fixes CO2 at the rate of plant growth. At a high enough CO2 concentration this process saturates, too.

What is not commonly appreciated is that there is an unbelievably gargantuan amount of fungal and bacterial ‘biome’ in the soil worldwide (as well as inside each of us in our intestines and colon) that interconnects plant roots and actually makes possible the fixing of CO2, by breaking down organics and minerals in the soil enabling plant roots to absorb nutrients they need to complete their growth cycles, which result in carbon being fixed into plant cellulose, and into soil carbonates. The TV show ‘Fantastic Fungi’ gives a visually stunning explanation of this, and is available here,, and here This plant-based natural process of “carbon capture” is disrupted and destroyed by chemical pesticide dependent industrialized monoculture farming.

I know it is a bitter pill to swallow, but the only real way to slow global warming in any noticeable way is to stop anthropogenic CO2 emissions FOREVER. There are no post-facto technological ‘capture’ or ‘remediation’ techniques that exist now or “could be developed” that would actually work as “silver bullets” of salvation; they would only ‘work’ as money making scams with which to gull those despairing of the ‘loss of easy living.’

Our best response to climate change is to change ourselves in every way possible and without ever looking back, like a butterfly emerging from its chrysalis — and to have fun doing so together. This has to be a willed conscious process because we do not have the luxury of a long timescale in a slowly changing world to allow the transformation of humanity to happen naturally through the unconscious genetically paced process of evolution.

But, with the right shared attitude, that much shorter timescale consciously willed personal and societal transformation could be more magical and take us to more wondrous new worlds than any fantasy of intra-galactic space travel at Warp Speed on the Starship Enterprise.