Post cites high CO2 levels in greenhouses to falsely claim that more CO2 is beneficial

At a time when the high level of carbon dioxide (CO2) in the atmosphere is emerging as a growing concern in a rapidly warming world, claims about the benefits of CO2 are increasingly gaining traction on social media. 

What is the claim?

A post on Facebook claims that high levels of carbon dioxide used in greenhouses are proof of the beneficial nature of CO2. The user posted an image of a greenhouse with text that read, "Are you still brainwashed into believing that CO2 is a bad thing? Here's a greenhouse pumped with CO2 at 1,400 ppm; More than 3 times, the normal level. MORE CO2 needed, not less.” The post has garnered 149 likes and 72 shares. An archived version of the post can be found here.

The Facebook post claims that more CO2 is needed, not less. (Source: Facebook/Modified by Logically Facts)

However, the claim is false. The comparison between CO2 levels in a greenhouse and the atmosphere in general is inaccurate. At excess levels, CO2 is a contributor to global warming and is detrimental to both plants and humans.

A reverse image search on the particular photo of the greenhouse used in the claim led us to a news report titled, “Community food gardens increase job opportunities and food security,” published on a South African news website on May 18, 2021. According to the caption, the particular photo shows a community food garden by the Sakhulwazi Women's Agricultural Cooperative. However, the news report does not mention whether the particular greenhouse shown in the photo was pumped with 1400 ppm of CO2. 

High CO2 levels in greenhouses

According to a fact sheet titled "Greenhouse Carbon Dioxide Supplementation," published by Oklahoma State University, while the natural carbon dioxide level in a greenhouse is 400 parts per million (ppm), CO2 levels are higher at night due to plant respiration and microbial activity, dropping during the day as plants use CO2 for photosynthesis. Increasing CO2 levels can boost plant yield, but excess CO2 is toxic to plants and humans.

David Des Marais, an MIT Professor who studies how plants respond to their environments, explained in the MIT Climate Portal, “Although plants need carbon dioxide to grow, their success in very high-carbon environments is not guaranteed. Not all plants like extra carbon equally.”

For most crops, the saturation point will be reached at about 1,000–1,300 ppm under ideal circumstances, according to a report by the Government of Ontario.

What do experts say?

Professor Kevin L. Griffin of the Department of Ecology, Evolution, and Environmental Biology at Columbia University explained to Logically Facts that it is wrong to cite high CO2 levels in a greenhouse to claim that high levels of CO2 in the Earth’s atmosphere are equally beneficial. 

While CO2 levels in a greenhouse do reach as high as 1,400 ppm in some cases, in the atmosphere, it is a completely different thing, he said. "It's important to remember that a greenhouse is temperature-controlled, and many plants are near their temperature limits. It's not the 1400 ppm CO2 alone that is the issue, it's the temperatures associated with a 1400 ppm atmosphere that is the problem. Similar statements can be made about other changes in the climate system associated with a high CO2 atmosphere, like changes in precipitation, evapotranspiration, nutrient availability, storms, wind, and light." Professor Griffin added.

A scientific study from the University of Colorado at Boulder found that outdoor CO2 concentrations of 930 ppm would lead to an indoor CO2 concentration of a harmful level of 1,400 ppm, which “may cut our basic decision-making ability by 25 percent, and complex strategic thinking by around 50 percent.” 

Noelle Selin, an MIT Associate Professor, stated in the MIT Climate Portal, "20th-century levels of CO2 are ideal, and humanity ought to aim for the atmospheric levels of a few decades ago, somewhere between 300 and 350 ppm.” The report also stated that in 2016, a worldwide body of climate scientists noted that a CO2 level of even 430 ppm would be over the line for avoiding dangerous climate change.

Dr. Partha J Das, a senior climate expert, told Logically Facts that CO2 being a plant food does not absolve it of its role in causing human-induced global warming. “Yes, CO2 helps plants produce their food through the process of photosynthesis. But the increase in CO2 from human activities and other greenhouse gases emitted from anthropogenic activities over the last 200 years has led to additional warming, which is now a matter of grave concern,” Das said. 

The verdict

The claim that CO2 is beneficial and that we need more carbon dioxide is false. Thus, while CO2 supply can be increased to promote faster growth of plants in a closed environment under specific conditions, it can also be detrimental to plants, and the same logic cannot be applied to plants and humans under natural conditions.