30 September 2023

Misleading: Although CO2 facilitates plant growth, excessive amount could be harmful as well

Experts say increased carbon dioxide impacts the natural ecosystem as a whole. The science of climate change has advanced since the 1920 experiment mentioned in the misleading tweet.

On June 25, a Twitter user shared more than a 100-year-old article from Scientific American, claiming that it has been known since 1920 that adding carbon dioxide to greenhouses or open air can facilitate a “huge increase” in plant growth with no harm supposedly inflicted on plants or animals.

The tweet, which gained more than 1,300 retweets and 2,600 likes, indicated it proves the climate emergency is a “hoax.” But this claim is misleading.

Carbon dioxide, often abbreviated as CO2, is a gas needed by plants for photosynthesis, a process in which plants create oxygen and energy along with sunlight and water. It is sometimes added to greenhouses in a practice called carbon dioxide supplementation to increase the growth rate of plants.

However, although added carbon dioxide can help plants grow, higher concentrations could do more harm than good, researchers say.

Benefits from the increased amount of CO2 can only be achieved with water, healthy soil and controlled temperature. Higher emissions of carbon dioxide, mainly from human activities, are also the main driver of climate change. This article from the Climate School at Columbia University says climate change can negatively affect various other factors vital to plants’ growth.

The 1920 article shared in the misleading tweet discusses the results of an experiment conducted in a greenhouse where carbon dioxide was added and other harmful chemicals such as sulfur were removed from the blast furnace exhaust gas supplied to the testing area.

In the said experiment the plants were reported to have grown larger than the control group. However, this is a perfect greenhouse environment. The real-world situation can be very different, as explained in this article from Climate Connections, an initiative at the School of the Environment at Yale University.

Annie Lab reached out to Pierre Friedlingstein, a climate scientist from the University of Exeter, and he wrote in an email on July 6:

“Elevated CO2 is good for plant growth indeed. No one questions that but the effect of increased CO2 on the climate system and impacts on natural ecosystems and human systems are more dramatic (and will continue to intensify with further climate change).”

“The 1920 study was good at its time but it only looked at the direct effect of increased CO2 on plant growth (potatoes, cauliflower,…). It did not consider the effect of climate change,” he added.

Friedlingstein said the Intergovernmental Panel on Climate Change is the “best source of knowledge” and its latest reports (here and here) detail the negative effects and impacts of excessive CO2.

The 1920 Scientific American article also mentions the same experiment in an open-air setting. It says increased atmospheric CO2 levels, known as the carbon dioxide fertilization effect, may facilitate photosynthesis.

However, modern research indicates the effect could also yield unexpected results.

As explained in this episode of SciShow (embedded below), faster growth and higher levels of carbon dioxide can change how plants produce useful or dangerous compounds.

The outcome is unpredictable and varies among different plants.

At the same time, rising temperature due to the enhanced greenhouse effect increases the risk of pests within ecosystems, especially in the Arctic, boreal temperate and subtropical regions, according to the Food and Agricultural Organization of the United Nations.

Studies also found that extreme weather events like heat waves and drought hinder the growth of plants, which offset the gain from the higher carbon dioxide concentration in the atmosphere.

A study conducted in 2010 by Georgia Southern University, meanwhile, points out that an increased level of atmospheric carbon dioxide could harm animals.

For example, marine organisms may find breathing difficult with more CO2 dissolved into the bodies of water. It may alter the food sources for birds and consequently harm the population.

Patrick Moore claims to be the co-founder of Greenpeace on his Twitter profile.

Patrick Moore, who made the misleading claim on Twitter, describes himself as a co-founder of Greenpeace. However, Greenpeace has issued a statement saying that Moore “does not represent” the international environmental protection organization and “did not found Greenpeace.”

Moore’s previous misleading claims related to climate change have also been debunked by some U.S. fact-checking organizations such as Politifact and Factcheck.org.

Note: This fact check was produced in collaboration with Science Feedback in France through its Climate Science Desk, an initiative supported by International Fact-Checking Network’s Climate Misinformation Grant Program.