Fact check: Excess CO2 harms plants more than helps them, experts say

The claim: More CO2 is better for plants

An Aug. 15 Facebook post (direct link, archive link) shows side-by-side images of a man standing next to a series of plants. The signs list higher numbers alongside larger plants.

"The fertilizer effect: all things being equal, more CO2 is better for plants, well into the thousands of parts per million," reads text included in the post.

The same image has been reposted several times, garnering hundreds of likes and shares over the last six months.

Follow us on Facebook! Like our page to get updates throughout the day on our latest debunks

Our rating: Partly false

CO2 has been shown to increase plant growth, experts said, but this growth has a limit. Adverse effects from excess CO2, like global warming, ultimately hurt plants more than help them.

Experts say CO2 stimulates plant growth – to a point

Several studies illustrate that plants grow more with a little extra carbon dioxide, both in controlled settings and in the natural environment.

However, there is a limit to how far this growth can go, said University of Nevada ecology professor Scott Allen.

In one experiment, plants initially grew larger with increased levels of CO2 but were "substantially compromised" as the amount continued to increase. Factors like water, light and nutrient availability affect how much carbon dioxide the plant can take in, said University of Texas ecologist Anthony Darrouzet-Nardi.

Fact check: Plants cannot absorb all the carbon dioxide emitted into the atmosphere

Darrouzet-Nardi said one can only claim more CO2 is better for plants by detaching the growth "from the other issues that carbon dioxide is causing," which is wrong. Carbon dioxide negatively impacts plants by contributing to the greenhouse gas effect and global warming.

"(It's) raising temperatures and potentially changing weather," Darrouzet-Nardi said.

Hot temperatures were found to overwhelm the positive effects of carbon dioxide on plants, according to Yale Climate Connections. Another study found that rice grown at high levels of CO2 had decreased nutritional value.

The negative consequences of climate change on plants are likely to outweigh any benefits from increased CO2, Scientific American reported.

USA TODAY has debunked a variety of CO2-related misinformation, including claims that carbon dioxide is too heavy to contribute to the greenhouse gas effect and that one eruption of Mt. Etna in Italy released 10,000 times more CO2 than humans ever have.

USA TODAY reached out to the social media user who shared the post for comment.

Our fact-check sources:

Thank you for supporting our journalism. You can subscribe to our print edition, ad-free app or electronic newspaper replica here.

Our fact-check work is supported in part by a grant from Facebook.

This article originally appeared on USA TODAY: Fact check: Excess CO2 harms plants more than helps them, experts say