Is Extra CO2 Good/Food for Plants?

Reflections on the latest DOE climate report: If we shrugged off anthropocentrism, we would see that CO₂-enhanced growth is not proof of a thriving biosphere, but a sign of its fever.

Heated Atmosphere

Two noteworthy documents are now stirring debate in the international climate community: the latest DOE climate report by Drs. J. Christy, J. Curry, S. Koonin, R. McKitrick, and R. Spencer, and another, less publicized but equally provocative and disruptive, paper by Drs. R. Lindzen and W. Happer.

In brief, both: (a) spotlight discrepancies between global climate models and actual observations, especially in tropospheric temperature trends (see my discussion of why this matters in my first ever substack post); (b) challenge the methods used to attribute extreme weather events to global climate change; and (c) argue that when records are extended to the early 20th century, current temperature extremes lose their exceptional status — implying that climate change is not the primary driver of some recent extremes. For example, the most severe U.S. temperature extremes are said to have occurred during the Dust Bowl.

Above all, however, both reports — though authored mainly by physicists (and one economist) — devote substantial attention to a central claim: that additional CO₂ benefits the biosphere, making plants grow faster, larger, and more water-efficient, thereby increasing agricultural productivity. That is the claim we will examine in depth today.

First, a disclaimer. These reports inevitably provoke strong reactions, and I respect those feelings. From my own experience, despite, or thanks to, modern advances in industrial agricultural output, many people today consume nutrient-poor diets (a point also noted in the DOE report, which I discuss further below) and may lack the nutrients needed for emotional balance — all the more so in a world where bad news dominates. Yet if one can set aside the emotional heat, these reports offer an intellectual feast: a rare opportunity to see an unusually wide spectrum of interpretations of the same climate data. Given the high-level nature of this mainstream critique, the mainstream will have to respond — revealing which points can be defended and which will prove more fragile.

As an initial, detailed public response, I recommend the document from Professor Michael MacCracken, which directly addresses the paper by Lindzen and Happer. It is available for all to read and judge for themselves.

Ecological astigmatism

While these documents cover a wide range of physical interpretations of climate phenomena, they all share what I would call ecological astigmatism — a distorted view of nature in which any increase in growth is mistaken for genuine health: the more, the better. I see ecological astigmatism not as the flaw of a few papers, or a limitation of physicists compared to biologists, but as a chronic condition of modern civilization — a distortion of vision that blinds us to life’s complexity. It spares almost no one, not even those who consider themselves ecological thinkers, and overcoming it requires conscious effort. (I recommend reading “How Do We Know the Truth” by Professor Chuck Pezeshki.)

To see why this perspective is misleading, let’s start from an economic parallel. Many people know that GDP (gross domestic product) is not a measure of collective well-being, and its growth does not necessarily mean society is progressing in any meaningful way. As Nate Hagens pointed out in “The 10 Core Myths Still Taught in Business Schools”, GDP simply tallies any activity measured in money. If an environmental disaster destroys a city, rebuilding it will add to GDP — and if extra work is needed, GDP growth will even be recorded as a result of the disaster. (Conversely, as Ugo Bardi notes, GDP as a measure of monetary exchange can rise while actual economic activity, measured by energy consumption, declines.)

A more natural example: imagine an anthill where ants live in quiet, orderly rhythm. Now picture someone jabbing a stick into their home. Suddenly, activity surges — workers rush to repair the damage, guards swarm to confront the intruder. It’s a burst of energy and movement, but hardly a sign of improved ant prosperity. It’s a stress response.

Similarly, a rise in biological activity at the ecosystem level is not automatically a marker of ecological health; it can be a symptom of strain. Which brings us to “CO₂ fertilization.”

If we can’t entirely shed our human frame of reference, think of Earth’s biosphere as a giant production line. Each year, plants and algae manufacture about 100 gigatons of organic carbon — roughly a trillion tons of fresh green biomass. Yet the atmospheric carbon reservoir is relatively small: only about 800 gigatons as CO₂. Almost all of that annual output is quickly consumed by bacteria, fungi and animals, which return the carbon to the atmosphere. This tight production–consumption loop kept preindustrial CO₂ levels stable; even a small, lasting imbalance would have sent them rising or falling.

We have now subjected the biosphere to a vast experiment — injecting enormous amounts of carbon dioxide into the atmosphere by burning fossil fuels at a rate equal to about one-tenth of what the biosphere synthesizes each year. How did the biosphere respond? Global carbon budget assessments tell us: it began producing extra organic carbon — carbon that, crucially, nobody consumed! (Think about it: the biospheric production line has ramped up output, but no one has claimed the surplus. How should we interpret that? What does it mean?)

As a result, a biotic sink for anthropogenic carbon formed, so atmospheric CO₂ now accumulates not at 10 GtC per year as we burn fossils, but at a significantly lower rate. I’ve covered these processes in detail in two earlier posts, which I invite you to read:

New Global Carbon Data Revives the "Missing Sink" Problem
Nature is trying to fix our mess—it’s time to recognize its power

Here, it’s enough to note that many people — including the DOE report authors — take this as evidence that “CO₂ fertilization” has made the biosphere bigger. Dr. Craig Idso, for instance, illustrates his point with photos showing plants grown under elevated CO₂ concentrations becoming larger (see below).

But a recent study by Bar-On et al. (2024) in Science — unmentioned in the DOE climate report — shows that global plant biomass has not increased over the past thirty years. This means something else is happening on a planetary scale: plants don’t grow bigger but are producing extra material that the rest of the biosphere does not consume, so it accumulates somewhere — likely in soils or in dissolved form in the ocean.

This fits perfectly with the biotic regulation concept: the biosphere treats excess atmospheric CO₂ as a disturbance and works to restore its optimal, lower concentration by removing it. Think of it as the biosphere’s fever — the same physiological response your own body triggers when threatened by toxins from harmful bacteria or viruses. Metabolic rates rise as the body fights to re-establish balance. Fever is not a sign of health; it is a sign of life under stress. The same is true for our biosphere — it is alive, and it is struggling. And yet we call it “CO₂ fertilization.”

Guess what happens if the body is never allowed to recover, but is continually reinfected and forced to sustain a fever for a long time?

Plant obesity?

Now, let’s keep bending our brains away from the “more is better” mindset and look at these photos from Lindzen and Happer (2025) meant to send a positive message about CO₂ being good for plants.

In the image above, a plant grows larger and larger as carbon dioxide levels rise. This looks like a good thing.

In the image below, four human bodies show a similar progression — but the largest is clearly obese, a condition linked to higher risks of numerous health problems. Bigger isn’t always better.

We often assume that ecosystems are limited by nutrients, which must sometimes arrive through extraordinary means — like the carcasses of dead salmon or dust blown across the Atlantic from the Sahara. (This is, incidentally, another anthropocentric idea, mimicking international trade, something that does not truly exist in nature.) But “more nutrients” doesn’t automatically mean “more success.” Plants that grow unusually large in nutrient-rich areas are not necessarily better off when it comes to long-term resilience. For example, Shuli Chen and colleagues found that in the Amazon, the trees most resilient to drought are the slower-growing species rooted in the less fertile soils.

Even if we neglect how the biosphere is doing but focus on our own short-term needs, relying on fast-growing plants that churn out poorly digestible extra biomass does little to improve our nutrition. The DOE report authors did acknowledge this — it is well known that our food has been losing nutritional value. While it still delivers (often poorly digestible) calories, it increasingly fails to provide the full spectrum of nutrients needed for a healthy body and mind to reach their full potential. The authors, however, brushed this aside, suggesting that depleted food can simply be “fortified” with vitamins. (They likewise dismissed concerns that prolonged exposure to elevated CO₂ levels might be harmful to human health and cognition (see, e.g., U. Bardi, P. Bierwirth, K.-W. Huang, and J. McIntyre 2025), arguing that acute effects have only been observed at concentrations much higher than current ambient levels. But chronic exposure is not the same as acute.)

Regarding the vitamins, indeed, the food supplement market is booming, but biologically active nutrient forms — unlike conventional synthetic vitamins — are not cheap, they are very costly. If we tally the effort and resources required to manufacture the “vitamins” now missing from our food, any supposed agricultural gains from “CO₂ fertilization” could easily vanish.

That said, I have long maintained that with our current population numbers, providing healthy food for everyone is likely impossible without destroying all remaining tropical forests. Any large-scale shift from industrial agriculture — with its maximized yields — to more natural, ecosystem-based farming will inevitably reduce productivity and raise global food prices. In nature, “better” is not “more”: when you respect natural laws, you must leave more for the ecosystem itself, and that portion is subtracted from your own yield. Paradoxically, today’s industrial agriculture — while delivering mostly poor but cheap calories and poisoning the soil — also partially, and temporarily, shields tropical forests by reducing the economic incentive to burn them for cropland. We live in an entangled world where good and evil walk hand in hand.

Outlook

I don’t have a clear-cut conclusion today. It is hard to live when the world feels saturated with bad news. One can either embrace the art of grieving or retreat into rationalization. The DOE climate report can be read as an attempt to counterbalance the doom-laden narratives of climate science by suggesting that things are not quite as dire as they are portrayed.

One of its strongest implicit arguments is that if we were to aggressively cut off fossil fuel supply tomorrow, billions of people would die. The debate here is not about whether climate change is harmful, but whether we can act aggressively without unleashing immense human suffering. Our civilization, like an addict, is deeply dependent on fossil fuels, and any abrupt withdrawal would bring severe pain. As fossil fuels naturally phase out due to their declining EROI, that pain might be less acute. Although I’m not certain. These are complicated matters.

But I do find some arguments naive — for example, claims that California is “going renewable” while importing $100+ billion worth of goods from China. China is not going renewable; it is expanding all forms of energy consumption, including coal — and in 2024, its coal demand reached a new all-time high. One could say California is going green at the expense of China going black.

I often think of a banner found all across Russian railways: “Remember! It is not possible to immediately stop the train!”. Once a train is thundering down the tracks, momentum rules — and sometimes it’s already too late to jump clear. In the same way, our fossil-fuel momentum carries us forward whether we like it or not. With all the uncertainties in play, I want to share the DOE report authors’ hope that the ongoing accumulation of CO₂ will not prove fatal for the biosphere as we know it (and I am thinking of the coral reefs in the first place, which the DOE report authors mistakenly claim to have been rebounding.)

Regardless of CO₂ accumulation, the Earth’s biosphere is gravely ailing under our direct assaults — logging, burning, and chemical poisoning. This reality is ignored (or exapátisiologized) by the climate mainstream, by their opponents, and, historically, by our civilization as a whole.

The chances that we could wipe out all life on Earth are small. Finding harmony with the biosphere is, above all, a matter of our own survival and continued progress as a thinking species. It seems that once our urbanized civilization reached a certain level of detachment from the natural world, we rapidly lost the capacity to process complex ideas. The greatest discoveries in science were made when people lived on the brink between urban and natural life — already enjoying the comfort of the former but still exposed to the complexity of the latter. This was also the time when classical music flourished.

I do not know whether a civilization truly in harmony with the biosphere is possible, but I want, at the very least, to raise my voice in its favor.