More CO2 in the Atmosphere Hurts Key Plants and Crops More Than It Helps

Yves here. The fact that more CO2 hurts the productivity of crops is probably old news to many readers, but this exposition may be helpful in discussing the impact with friends and family.

By Karin Kirk. Originally published at Yale Climate Connections

ake a look out the window and it’s easy to see how people are changing the landscape. The human fingerprint touches almost every part of the globe. We’ve also shaped the planet in ways that aren’t visible: Human activities have actually changed the composition of the atmosphere. Carbon dioxide (CO2) is an important component of the atmosphere, and human activities have increased the amount of this gas in the atmosphere by 45% since widespread industrial activities began in the mid-1700s.

This is important because CO2 plays multiple roles in keeping Earth’s climate stable. Nature is a carefully balanced system, and over the years, humans have disrupted this balance. Thankfully, we also are capable of reducing our impact – especially now that we understand more about how the Earth system works.

But you may have heard a myth that nature’s balance doesn’t really matter. After all, CO2 is natural, and it helps plants and crops grow. That’s true. But it’s also misleading in that it’s only part of the story. A widely circulated myth suggests that adding extra CO2 to the atmosphere will fertilize plants and crops and make the world greener and better. Unfortunately, that turns out not to be true.

The myth that CO2 is plant food and that “extra” CO2 therefore can’t be bad is an example of a logical fallacy. It sort of sounds right, but it’s a major oversimplification. It’s appealing because it suggests that it’s okay to emit the pollution that causes climate change. But the myth is not true. It’s so oversimplified that it leaves out other important factors that help plants grow – and all of the damage that extra CO2 is causing. Just think of it in terms of “too much of a good thing is a bad thing” as, for example, with too much water causing a bathtub to overflow.

Fertilizer Alone Does Not Make a Successful Garden

A lot of myths have a grain of truth to them. That’s part of what makes them believable – at first. But it’s up to us to look beyond that single fragment of a fact. In the case of the CO2-as-fertilizer myth, you can test the idea by thinking about your own garden. Is fertilizer alone sufficient to create a healthy garden? Of course not. A garden needs the right amount of water, stable weather conditions, and plants that are suited to the local environment. These are the same factors that have been disrupted by an overload of CO2 in the atmosphere. For example, just adding more fertilizer doesn’t help plants when a garden is getting either too much or not enough water.

CO2 Is Natural, But Can Also Be Harmful

Another facet to this myth is that CO2 is natural, so therefore it can’t be a bad thing. Again, a “gut check” can show how that logic doesn’t hold up to scrutiny. For example, nitrogen and phosphorus are also plant fertilizers, but they’re pollutants when there’s too much of them. An overdose of nitrogen or phosphorus triggers algae blooms, kills fish, and turns lakes into smelly swamps. Even oxygen is explosive in high concentrations. Many serious pollutants – mercury, lead, arsenic – are naturally occurring. But they’re still dangerous. The same holds true for CO2, and it’s both a natural, necessary substance and a pollutant in high concentrations.

It’s All About Balance

Nature is like a recipe, with each ingredient needed in just the right measure. A pinch of nutmeg gives pumpkin pie a rich, warm flavor, but a tablespoon of nutmeg would ruin the pie. A car’s engine runs on a precise blend of air, fuel, and spark. Overloading one element disrupts the whole system. Many aspects of nature operate in a similarly balanced way.

For example, the atmosphere has a specific recipe. CO2 and other greenhouse gases are an essential part of the recipe because they trap heat in the atmosphere. With no CO2 Planet Earth would be in a perpetual ice age. But a small amount of CO2 keeps the planet in the famous “Goldilocks and the Three Bears” condition: not too hot, not too cold, but the “just right” zone that’s ideal for life as we know it. Too much CO2 overheats the planet.

By studying Earth’s history, scientists have learned that when there was a lot of CO2 in the atmosphere, the planet was hot. In fact, the last time the Earth had as much CO2 in the atmosphere as it now does was the Pliocene Epoch, more than 3 million years ago. At that time, Earth’s atmosphere was 3.6 to 7.2 degrees Fahrenheit warmer (2 to 4 degrees Celsius) than it is today. And global sea level was 50 to 80 feet (15 to 25 meters) higher.

Climate Change Is Hard on Plants

The basics of climate change are actually easy to understand. Human activities emit around 100 million tonsof CO2 every day, mostly by burning fossil fuels, which causes the atmosphere to trap more heat. As a result of that heat-trapping pollution, the atmosphere, land, and oceans have all become warmer. The added heat triggers side effects like more intense rainstorms, floods, prolonged heat waves, and droughts. In turn, those unpleasant conditions lead to more frequent and severe wildfires, insect outbreaks, and crop failures. Sure, today’s plants have a bit more fertilizer from the extra CO2 in the air, but that additional CO2 causes many other problems, harming many plants and crops. Climate change is disrupting plant growth.

Agricultural Experiments Show Negative Effects

Scientists have performed many experiments to see what happens when plants and agricultural crops receive extra CO2. When supplemental CO2 was pumped into the air around plants, they grew faster. For this reason, CO2 is sometimes piped into enclosed greenhouses to boost production. But greenhouse plants also have optimal amounts of water, excellent soil, and controlled temperatures. It’s usually a different story out in the real world.

To conduct a more “real world” experiment, other studies have given plants extra CO2 plus an increase in temperature. In these conditions, many plants and crops grew poorly. In most cases, the boost from CO2 was overwhelmed by the hotter conditions. These experiments demonstrate that the myth of CO2 fertilization is false, and peer-reviewed reports find that major crops like wheat, rice, corn, and soybeans will become less productive as the world heats up.

Likewise, a landmark study in 2018 found that growing rice in high-CO2 conditions makes it less nutritious. As a basic grain, rice plays a critical role in feeding the world’s population. The extra CO2 caused an imbalance within the crop’s chemical makeup, which resulted in rice that had lower amounts of protein, iron, zinc, and B-vitamins. “The entire elemental balance is out of whack,” explained plant physiologist Lewis Ziska, an author of the study. This result is yet another example of how the recipe of nature is being disrupted by excess CO2.

Bad News Can Lead to Our Making Needed Changes

Myths that try to “disprove” climate change can be appealing. Nobody loves the idea that human-caused pollution is now altering the chemical balance of Earth’s atmosphere. Nevertheless, climate change is happening.

But we can use our improving knowledge to prevent these problems from getting worse and maintain a healthy climate for plants and people.

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  1. vlade

    Hmm. I take an issue with this. Not necessarily with the conclusion, but with the presentation.

    “Nature is a carefully balanced system”. No, it’s not. If it was, we would not have evolution, because in a stable system all evolutionary niches are filled already.

    “Nature is like a recipe, with each ingredient needed in just the right measure.”
    See above. In the history of the earth we had numerous “recipes”, even within human written history.

    Nature is constantly changing, with organisms evolving to fill niches, whatever they might be based on the existing ecosystem and external conditions. Ecosystem is not a stable, passive thing. It’s an extremely dynamic system.

    What is important to understand is that human changes – of which there are many – are changing that ecosystem too, often very fast. That doesn’t mean that at the end there will be no ecosystem – action of every part of the ecosystem change it, always. There will an ecosystem.

    But it may well be “incompatible with human race survival”.

    And that actually doesn’t mean just CO2, it means monocultures and general drop in diversity (although it doesn’t mean diversity will never get back, after the extinction events it is, but it takes millions of years), suspectibility to pandemics from overpopulation and fast transmission vectors and all sort of things.

    I really really dislike this type of presentation, as it’s extremely anthropocentric, and has undertones of we(humans) are special and entitled. “Nature is stable for us humans.” “We’re destroying Nature”.


    Nature doesn’t care about us. It doesn’t care about anything or anyone. It just is, and it would take societies orders of magnitudes more powerful to destroy it, if it even can be done. If humans manage do destroy most of the life on the planet, to nature it will mean nothing, and even to the planet it will be just another extinction event which it had few already, and will have a few more in its future no matter what we humans do (if nothing else, I can’t image we’d ever stop thermal death of the universe, ignoring things like Sun going red giant etc., so there you go).

    We’re speck of nothing in the universe of nature, no more special than any other natural phenomena, entitled to nothing, and in the overall course of things irrelevant to it – except to us. And that’s the tragedy of it.

    We can only be relevant to ourselves, but we still can manage to destroy ourselves. No sense of self-preservation, nothing.

    1. juno mas

      I’m in general agreement with your broad view of nature and the “ecosystems” of the planet. Earth is a constantly changing symphony of Discordant Harmony; experienced over centuries, if not millennia.

      I think the article is trying to express a disdain for simple concepts: more CO2 is good, when it ain’t. Because it upsets the current ecosystem that satisfies our present human population. Extra CO2 in the atmosphere creates an increase in acidification in the oceans which can negatively impact marine productivity that provides food for that human population. It’s all connected, isn’t it.

      The complexity of ecosystems is confounding most of mankind.

      1. Arcturus

        I broadly agree with you and with the original post, but something that always catches my eye is the use of hyperbolic, disingenuous or downright misleading language in the climate debate, which I think you have inadvertently done. When you say that “extra CO2 in the atmosphere creates an increase in acidification in the oceans” it implies that the oceans are acidic and are becoming increasingly acidic and conjures images of poor shelled creatures dissolving in an acid bath. As it happens, the oceans are alkaline and at most they are becoming a little less alkaline, although I understand the current range of alkalinity is within ranges provided in textbooks from multiple decades ago.

        The article itself is very disappointing. It basically creates an argument that no-one relies on in the first place and then does an extremely poor job of trying to refute it. Towards the end it seems to confirm that the argument is actually true anyway.

    2. Elcil

      “We’re speck of nothing in the universe of nature, no more special than any other natural phenomena, entitled to nothing, and in the overall course of things irrelevant to it – except to us. And that’s the tragedy of it. ” …you say.

      I do like your comment, despite the nihilism…
      Yes, unfortunately, we will most likely destroy ourselves.

      What is the tragedy?

      We are a speck of natural phenomena and are not entitled to anything more than any other speck, as it were. All natural things must find it’s niche to survive / thrive. You have reduced Humans (your word) to just another speck of natural phenomena. We are so much more than that. We Humans, as you call us, have developed The Arts. While this may only matter to ‘us’, it is special. The Arts are the most important evolutionary incident(?), even if the entire universe implodes in a reverse fireball tomorrow.

      We may be the only phenomena that knows it is a phenomena.
      We are special. Not better, not more deserving, but special.
      You are special.

      1. vlade

        We are no more special than anything else is special.

        Birds can fly, unassisted. Ants can carry mutiple of their weight, unassisted. All sperm whales can dive deeper than all but a vanishingly small part of human race ever did. Deep sea vent microbes can live w/o any sunlight. Everything is special.

        We do not even know that we’re the only penomena it knows it’s a phenomena, to be honest. And that’s just on our planet. There’s a non-trivial chance that in the vastness of the universe there was, is, or will be something similar. Maybe even with arts (or, at least what they consider arts).

        TBH, I don’t see it as nihilism.

        I see it as a reason why we should take more care about ourselves, exactly because nothing else will, and if we don’t make it so that we matter to ourselves, nothing else will either. It’s the same reason as why we should fight for justice – even though if you took the whole universe apart, you’d find no speck, not a single particle of justice. It’s there only when, and if, we care.

    3. Basil Pesto

      Agree 100%, I find that kind of framing really obnoxious, not to mention insultingly reductive (harp on the ~nature is in balance~ theme long enough and you start to sound like a character in Star Wars talking about the force). Ditto the “we’re destroying the planet!” framing. The planet will be just fine (until, as you say, the ‘death’ of the Sun).

      This all sort of begs the question, even though we are ‘aware’ of the fact that we are changing the climate, is it actually within our power as an animal to do anything about it, that is to say, to voluntarily modify our behaviour at a massive scale to slow down the changes we’ve put into effect? Theoretically, it surely is, but in the real world? The argument “well, we were around before the industrial revolution” is irrelevant – there’s no putting that toothpaste back in the tube. I wonder if it’s any more possible than it was for the organisms that caused the Great Oxygenation Event to stop giving off oxygen.

      1. drumlin woodchuckles

        Well . . . . the Merchants of Fossil were very afraid that it WAS possible. Which is why they spent several decades flooding the zone with billions of dollars worth of pro-fossil hasbara and FUD-clouding the rising tide of knowledge and information.

        Is it still possible NOW? After the Merchants of Carbon have brought us to within several years of Extreme DeFossilization or Heat Death of Civilization? The Merchants of Fossil are hoping that it is Not Possible. That is why they worked so hard to delay addressing the problem for so long . . . . in order to bring us all to the Too Late Now Anyway event horizon.

        The only hope would be for a National Greenism In One Country movement to take over the US and legally democratically disempower other movements and trends. Such a movement would then take America out of every Free Trade Agreement and Organization and build a Great Green Wall of Protection around America against all our Carbon Dumping Trading Enemies. We would have to build an economy as small as Net Carbon Suckdown constrained it to be. That would require crushing, perhaps physically exterminating, every rich person who objected to that threat to their lifestyle.

  2. Lee

    Scientists have performed many experiments to see what happens when plants and agricultural crops receive extra CO2. When supplemental CO2 was pumped into the air around plants, they grew faster. For this reason, CO2 is sometimes piped into enclosed greenhouses to boost production. But greenhouse plants also have optimal amounts of water, excellent soil, and controlled temperatures. It’s usually a different story out in the real world.

    Using greenhouses as powerstations to provide electrical power for us and perfect growth conditions for the plants to soak up the CO2 and not release it to the greater atmosphere. Use the ground as a thermal store and you have a reliable power source.

  3. drumlin woodchuckles

    I used to speak of ” CO2 skydumping” as if CO2 were some kind of garbage. But now I speak of ” CO2 skyflooding” to acknowledge that CO2 is a good thing, and too much of it all at once in the wrong place is too much of a good thing.

    CO2 skyflooding is “like” water landflooding, in that water is a good thing and too much of it all at once in the wrong place is called a “flood”.

  4. JeffK

    The relationship between net photosynthesis and CO2 concentration is not linear. Above 400 ppm the rate of net photosynthesis diminishes. That’s a relationship that has been known since the 1960s. A more important non-linearity regarding CO2 is the relationship between atmospheric temperature and water holding capacity of the atmosphere. As the temperature increases linearly the water vapor pressure demand on plants increases exponentially. As you probably know, Plant use photons to split water molecules and fix carbon. But if the vapor demand of the atmosphere is high, plants close their pores to limit water loss. If plants experience water stress over a long period of time during the growing season they well grow poorly and produce less harvestable material. people tend to think that a couple of degrees centigrade temperature increase might be tolerable – even desirable, but as we have witnessed recently in dealing with the pandemic, we have a hard time conceptualizing exponential increases in things. (If only we could get our heads around population growth).

    CO2 is no more “fertilizer” than oxygen is “food”. That’s an inane characterization that has even been spoken in the halls of congress. Oxygen is the fire that burns up carbon-carbon bonds within animals; complex carbon molecules which plants linked together through photosynthesis. Plants need and utilize nitrogen and metal ions as “fertilizer”. Without CO2 we would not be here. Too much and we are toast, too little we starve. Its an insanely delicate balancing act and we’ve got to get out *hit together before we screw it all up!

    What Vlade said +1

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