CO2 use in greenhouses does not disprove harm on climate

"The ideal CO2 level for growing food is 400ppm & 600-1000ppm is used in greenhouses to increase yield by over 30 percent & reduce pests & diseases," says text over a video shared July 20, 2023 on Instagram. "Yet climate scientists tell us 350ppm is so dangerous we will all starve. Question everything."

The clip shows footage of tomatoes in a greenhouse. The post's caption says: "Why do they really want to cut carbon? Maybe to starve us?"

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Screenshot of an Instagram post taken August 1, 2023

Similar claims have circulated on Facebook and Twitter, which is being rebranded as "X," as well as in blog posts.

The process of adding CO2 to a greenhouse for the purpose of increasing plant productivity is known as the carbon fertilization effect (archived here). But Are Olsen, a professor at the Bjerknes Centre for Climate Research in Bergen, Norway, told AFP the technique is incomparable to CO2's impact worldwide.

"Greenhouses have controlled temperatures, watering systems, fertilizer levels, etc -- while natural environments do not," he said August 2.

Scientific studies have demonstrated how increases in atmospheric CO2 have negative effects on plants and the planet as a whole.

"It is unequivocal that human influence has warmed the atmosphere, ocean and land," the United Nations Intergovernmental Panel on Climate Change (IPCC) said in the first part of its 2021 report (archived here).

'Cherry-picking information'

Rising CO2 is associated with higher temperatures and could increase the risk of extreme weather events (archived here). Most scientists agree recent changes in the climate are due to greenhouse gas emissions linked to human activity (archived here).

Olsen said that, contrary to the Instagram post, scientists "have never claimed that reaching 350 (parts per million) will lead to a detrimental loss in global food production."

"The current atmospheric CO2 concentration is 419 ppm. It is rising by 2 ppm each year, so if emissions continue unabated, the levels mentioned in the post is easily reached -- at least for 600 ppm," he said, noting that is the level at which such effects will begin.

Vivek Arora, a research scientist in Canada studying carbon-climate interactions, told AFP about 50 percent of human-caused emissions have stayed in the atmosphere.

"The rest have been absorbed by the land and the ocean. Had land and ocean not provided us with this ecosystem service, the current concentration of CO2 would have been much higher," he said August 1, describing the Instagram post as "cherry-picking information."

Higher CO2 levels help plants photosynthesize more, Arora said. But if plants face extreme conditions -- such as water shortage, heat and drought -- they cannot absorb the gas in the same capacity, regardless of how much is in the atmosphere.

Delphine Deryng, a lead author of an IPCC chapter on food and ecosystem products, told AFP that "elevated CO2 cannot be dissociated from changes in temperatures and precipitation extremes and variability."

The National Oceanic and Atmospheric Administration (NOAA) calculated that the direct warming influence of human-produced greenhouse gases had risen 49 percent between 1990 and 2021. About two-thirds of that heating imbalance was due to carbon dioxide, according to the US agency (archived here).

"The benefits of elevated CO2 could be quickly overturned by rising temperatures," Deryng said July 28.

'No upsides'

The carbon fertilization effect is controversial for its impact on climate and the nutritional value of crops.

Deryng said crops under elevated CO2 often require additional irrigation and fertilizer application, often in the form of synthetic nitrogen. Nitrogen use, in turn, produces additional greenhouse gas emissions (archived here).

That tactic "is not sustainable at all and would accelerate risks posed by climate change," she added.

Using CO2 to boost crops may also lower their nutritional quality (archived here).

"Field experiments on wheat and rice indicate that a doubling of CO2 from preindustrial concentrations would reduce protein about 10 percent and would reduce B vitamins about 30 percent," said Kristie Ebi, a professor at the University of Washington Center for Health and the Global Environment, on July 28. "While these plants grow faster, their nutrient density declines."

Ranga Myneni, a professor in Boston University's Department of Earth and Environment, previously told AFP that focusing on a "short-term effect of enhanced plant growth from higher CO2 concentration misses the important point."

"CO2 is a greenhouse gas, it is causing climate change whose effects include global warming, loss of sea ice, rising sea levels, etc.," Myneni said. "There are no upsides to high CO2 concentration in the atmosphere."

AFP has investigated other false and misleading claims about climate change, including a similar allegation about CO2 effects.