Is carbon dioxide good for plants?

Lewis H. Ziska, associate professor at Columbia University’s Mailman School of Public Health, had to quit the U.S. Department of Agriculture after 25 years of service in 2019 to protest interference by the Trump administration in his research on the negative effects of rising carbon dioxide on nutritional composition of rice. Published in Science Advances, a top-notch scientific journal, the research found that increased carbon dioxide in the atmosphere reduced Vitamin B and E in rice plant which could impact 50% of daily calorie intake by more than 6 million rice eaters in the world. In his book Greenhouse Planet, he captures all that went behind the research while stressing the urgent need for investigating the climate-denying mantra that carbon dioxide feeds plants and greens the planet. Prof. Ziska responded to questions on the wider implications of his research on plant biology as seen from the climate change lens.

Will shifting focus from sea level rise to plant biology, as you have suggested, not compromise the current commitments on emission reduction to some extent as it will support the climate change deniers’ claim that ‘CO2 is plant food’?

I am hoping it will strengthen those commitments---showing that CO2 is plant food for poison ivy, or for Parthenium—or can reduce the nutritional content of rice will, if anything, bring scientific scrutiny to the assumption that ‘CO2 is plant food’, and challenge deniers’ claims.

COP27 advocated progress on the issue of loss and damage caused by extreme events, counting emission reduction targets as an ongoing work. While the role of plant biology is undoubtedly significant, will it get the desired attention?  

Fair point---it won’t get the attention it deserves unfortunately. It’s hard to compete with extreme events, droughts, floods as they are visually compelling. Watching slow changes in plant species distribution, or nutritional changes in your rice bowl, while very important, don’t capture that level of dramatic immediacy.

Prof. Lewis Ziska

You argue that as CO2 stimulates growth and yield, it diminishes nutritional quality. Climate deniers might read the first half of the statement and rejoice at the prospect of getting more crops.   

It’s important to consider that in the plant kingdom, as with the animal kingdom, competition is important.  If you farm you recognize that the biggest physical effort is to reduce weeds, as weeds are the primary limitation on crop yield.  As CO2, the source of carbon for plant growth increases, it isn’t just crops that are affected. In a majority of studies to date, it is the weeds, not the crops, that are the ‘winners’ and crop yields are negatively affected.  So, while individual plants can respond, in a field situation, the weeds, with their greater ability to adapt to change, may pose an even greater threat to food security.

By your own admission, recent and projected CO2 increases in the atmosphere can stimulate the growth of some basic cereals (viz., wheat, rice, soybeans) as well as many weeds. Isn’t it an interesting tradeoff for sequestering more carbon from the atmosphere?

Yes. One piece of good news, many of the worst weeds are simply wild relatives of the crop. For example, in rice, the worst weed is Red Rice, or weedy rice.  Right now we have data suggesting that weedy rice has already responded strongly to the 25% increase in CO2 since 1970, i.e. it yields more than the cultivated rice lines which respond roughly by about 10%.  Suppose we knew why —could we look for those characteristics in weedy lines as a means to increase yields (and sequester carbon) in cultivated rice through breeding?  Can crops ‘learn’ from their weedy cousins?

Climate change has been made to seem like a black-and-white issue whereas in reality it is complex. How best to communicate science especially when it’s about crops that affects hundreds of millions of people?

Great question---and a difficult one. Communicating science isn’t about the esoteric or the what might be. It is about linking the science, especially food science, to climate and CO2 increases. These links include production (of course) but also nutrition (CO2 effects) and food safety (temperature effects on pathogens). My experience has been that if you can relate these scientific issues directly to what you consume at the table; then climate/CO2 takes on a very real and immediate meaning.

How to 'vote for science' when the almost 'certain' science behind climate change has become 'uncertain', with the effort to discredit science has become more intense? How to deal with it in the post-truth era? 

Respectfully disagree, perhaps there is greater effort to push back and discredit climate science, but climate change has, if anything, become more certain. It is the science of CO2 and plant biology that needs greater explanation and exploration beyond the simple ‘CO2 is plant food’ meme. 

But the scientific bottom line is simple:  If you think that the science of climate change (or CO2 effects on plant biology) is wrong---proof it. Write a hypothesis, test it, tell us how you tested it (so we can see what you did), and publish the findings after other experts have looked at your work. Lots of bloggers will talk about how climate science is wrong---but to date I am unaware of any who have published in the peer review literature showing that anthropogenic climate change is not occurring.

The Greenhouse Planet
by Lewis Ziska
Columbia University Press, New York
Price: Rs. 2130, Extent: 240 pages

First published in The Hindu on March 19, 2023.