Climate

CO2 can increase plant growth in greenhouses while also negatively affecting ecosystems and human societies

Posted on: 2020-03-19

Key takeaway

CO₂ can increase plant growth but its effects, which decrease with higher concentrations, are limited by the availability of other plant nutrients, such as nitrogen and phosphorus. CO₂ emissions can negatively impact natural ecosystems through global warming—e.g. by increasing evaporation and drying up soils in some regions or increasing heavy precipitation in others.

Reviewed content

Verdict:

Flawed reasoning

Claim:

CO2 is a plant nutrient...it’s not a pollutant that threatens human civilization. If CO2 was so terrible for the planet, then installing a CO2 generator in a greenhouse would kill the plants.

Source: Natural News, Mike Adams, 2013-06-22

Verdict detail

Flawed reasoning: CO₂ can increase plant growth in a greenhouse, but the argument that CO₂ is not harmful to the planet because plants don’t die is flawed. To assess the overall impact of CO₂ emissions on “human civilization”, effects on ecosystems and human societies should also be taken into account.
Misleading: Plants require CO₂, water, and other nutrients to grow. Although CO₂ emissions can increase plant growth in some regions, they also increase heat stress, water stress, and pest prevalence.

See our method of evaluation

Full Claim

CO2 is a plant nutrient...it’s not a pollutant that threatens human civilization as has been ridiculously claimed by global warming doomsday pushers. CO2 actually increases plant yields, accelerates "re-greening" and improves reforestation of the planet. If CO2 was so terrible for the planet, then installing a CO2 generator in a greenhouse would kill the plants.

Summary

The claim that CO₂ is a plant nutrient and not a pollutant appeared in an article published by Natural News in June 2013, and has gone viral in 2020 with over 1.6 million shares on Facebook over the past three months. This claim uses flawed reasoning to argue that elevated levels of CO₂ are not bad for the planet because it doesn’t kill plants in a greenhouse.

Although CO₂ can increase plant growth in a greenhouse, this effect does not necessarily apply to more complex natural environments where the benefits of CO₂ can be outweighed by nutrient limitation and negative climate impacts, such as increasing water stress, heat stress, and the prevalence of pests and pathogens. In order to assess the overall impact of CO₂ on the planet, all known effects of CO₂ on land ecosystems and human societies should be evaluated, instead of focusing on just one aspect as this claim does^[1,2,3,4].

Vegetation has absorbed some of the CO₂ emitted by human activities and converted it into leaf biomass, particularly in southeast North America, the northern Amazon, Europe, Central Africa, and Southeast Asia, as seen in the figure below^[1].

Figure- Increased CO₂ emissions have increased plant growth (leaf area index (LAI)) around the world. From Zhu et al. (2016)^[1].

But in addition to CO₂, plants require water and other nutrients to grow. Scientific studies show the effects of CO₂ on plant growth depend on the availability of other nutrients, such as phosphorus and nitrogen, as seen in the figure below^[2,5,6].

Figure- Under high concentrations of CO₂ (RCP8.5), crop models (GGCMs) predict that nitrogen (N) stress will reduce crop yields (%) in 2070-2099 relative to yields from 1980 to 2010. From Mbow et al. (2019)^[2].

CO₂ emissions are also predicted to produce less nutritional crops and reduce crop yields over time^[2]. “While increased CO₂ is projected to be beneficial for crop productivity at lower temperature increases, it is projected to lower nutritional quality,” according to the IPCC report on food security^[2]. Because CO₂ emissions contribute to global warming, crop yields are predicted to decline with increasing temperatures due to increases in heat stress, water stress, and the persistence of pests and pathogens, as seen in the figure below^[3,4].

Figure- A meta-analysis of 56 studies predicts that crop yields for maize, rice, wheat, and soy decline as temperatures increase relative to local baseline growing-season temperatures. From Moore et al. (2017)^[4].

More broadly, increases in plant growth due to increased CO₂ emissions may be offset by negative effects on land ecosystems due to rising global temperatures, prolonged droughts, and increases in intense rainstorms^[2,6]. In tropical and semi-arid regions, even moderate increases in temperature could lead to drier conditions that induce water stress, disrupt plant reproduction, and reduce crop yields^[7]. Nitrogen stress due to soil degradation is predicted to result in even greater declines in crop yields in the tropics^[2].

Additionally, the effects of climate change are not limited to terrestrial plant productivity. Impacts on weather extremes, coastal infrastructure, human health, and marine ecosystems—among other things—are also relevant to the question of whether CO₂ is a “pollutant that threatens human civilization”, in the article’s words.

Scientists’ Feedback

Pierre Friedlingstein

Professor, University of Exeter

[Comment from a previous evaluation of a similar claim.]

This is the usual misleading argument that if CO₂ is good for plants, it cannot be bad for the climate. CO₂ is needed for plant growth (along with water, nutrients, and energy from the sun)—but it does not change the fact that CO₂ is a greenhouse gas. It increases the radiative forcing of the planet and leads to warming, as observed over the last century^[6].

Frances Moore

Assistant Professor, University of California Davis

[Comment from a previous evaluation of a similar claim.]

In a meta-analysis of over 1,000 studies of the effects of climate change on agriculture, we find that, while CO₂ is beneficial for crops, this effect rapidly decreases with increasing concentrations^[4]. The net effects of climate change on agriculture, including both the benefits of CO₂ fertilization and the negative effects of warming, is negative for almost all regions. The effects of CO₂ emissions on agriculture cost approximately $8.5 per ton, even accounting for the positive effects of CO₂ fertilization.

Sara Vicca

Postdoctoral research fellow, University of Antwerp

[Comment from a previous evaluation of a similar claim.]

Plants don’t only need CO₂ and water, but also nutrients like nitrogen and phosphorus. If the latter are not sufficiently available, plants may not respond to elevated CO₂ at all^[5,6]. Moreover, climatic changes (and particularly extreme events) are an important threat to ecosystems and to the land carbon sink^[2,3,7,8].

Alexis Berg

Research Associate, Harvard University

[Comment from a previous evaluation of a similar claim.]

Yes, we are seeing an increase in vegetation around the world, with satellites showing up to 50% of the land surface greening over the last 30 years, most of it being indeed attributed to increased atmospheric CO₂^[1]. This is not a surprise. This vegetation increase is consistent with the fact that we know that about a quarter of our CO₂ emissions is being taken up by the land biosphere (another quarter going into the oceans, and the remainder staying in the atmosphere). This greening is taken into account in climate models. The real question is how long this greening is going to go on (there are already indications that it is slowing down), as we expect that as climate warms further, adverse impacts on ecosystems may start to offset the positive impact of increased atmospheric CO₂—particularly in places where regional climate is moving away from the “comfort zone” of current ecosystems.

Amber Kerr

Researcher, Agricultural Sustainability Institute, University of California, Davis

[Comment from a previous evaluation of a similar claim.]

CO₂ is not a pollutant in the sense of being acutely toxic to life, but this framing is highly misleading. Water is also non-toxic and essential to life on Earth, but too much water in the wrong places can be devastating.