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Is More CO2 Better For Plants Or Not?

Updated on February 2, 2017
Picture about CO2 benefiting plants, compiled by Robert G. Kernodle from public sources
Picture about CO2 benefiting plants, compiled by Robert G. Kernodle from public sources

Nutrient Or Nemesis?

A particularly troubling claim about human-caused climate change is that more CO2 in Earth's atmosphere will reduce the nutrient content of plants, in some cases, even reducing plant growth and diminishing overall plant health. This claim clearly defies reasoning in horticultural practices, where growers routinely infuse greenhouses or other crop areas with considerably-higher-than-ambient levels of CO2, ... seemingly to good effect, in terms of increasing plant sizes and increasing crop yields.

Such a blatant conflict of perceptions has annoyed me to the point of trying to resolve things once and for all, at least, in my own thinking. So, toward this end, I have done some homework that I hope provides additional clarity to an issue that just won't go away.

Some readers might have been through this all before. Some might never have considered the issue. Some might benefit from a timely re-hashing of it.

Those Who Say CO2 Is Bad

Picture symbolizing CO2 as a demon, compiled by Robert G. Kernodle from public sources
Picture symbolizing CO2 as a demon, compiled by Robert G. Kernodle from public sources

Proponents of CO2-induced climate change generally declare that increasing atmospheric CO2 poses a threat to plants. Who is saying this? What is the evidence? Where is this evidence written? Why should anybody believe it?

As an example, consider a 2007 article on the NEW SCIENTIST website ... [downloaded 01/30/2017]. Here David Chandler and Michael Le Page use a demeaning title, Climate myths: Higher CO2 levels will boost plant growth and food production to frame their presentation of information that contradicts the title's main suggestion -- that CO2 benefits to plants is a "myth". After clearly discussing a well-known CO2-fertilizing effect on plants, they proceed to use language that raises doubt, without effectively supporting the premise of their title. These authors further confuse the issue by diverting focus to factors such as temperature and water, which limit the CO2-fertilizing effect, a fact that is NOT disputed by those who understand the effect.

Consequently, the only myth that these authors reveal is that a demeaning title stands up successfully to detailed scrutiny of the information that it claims to represent -- it does NOT. Rather, a demeaning title without substance to support it merely provides an official reference for people who look no further than a title for the truth. This article, then, in my judgment, is a sham, an avoidance of, and misrepresentation of the most relevant real-world facts.

Feng et al. Paper

Now consider a frequently cited 2015 study by Zhaoshong Feng and others, titled, Constraints to nitrogen acquisition of terrestrial plants under elevated CO2, GLOBAL CHANGE BIOLOGY (2015), 21, 3152–3168 ... [downloaded 01/30/2017]:

  • On page 3161 of this study, the authors state: The findings that plants in eCO2 [elevated CO2] often take up more N and that large growth stimulation by eCO2 is accompanied by enhanced N acquisition have been emphasized in previous studies (Norby et al., 1999; Luo et al., 2006; Finzi et al., 2007; Iversen, 2010) and will not be discussed further here. Instead, we will focus on the finding of a negative effect of eCO2 on plant Nac [nitrogen acquisition] and N concentration at neutral or modest shifts in productivity.

This is just one example of how the authors of this particular study CHOOSE to focus on negative effects.

As I attempted to navigate the tedious, torturous, obscure academic writing style of the study, I never got a sense that the authors were making any final conclusive remarks condemning CO2 fertilization. Yet, popular science publications misrepresent this study or enlist individual experts who themselves appear to misrepresent the study in their personal quotations of it.

Feelings Overshadow Facts

An article at the website of SCIENCE DAILY, features the headline, Increased carbon dioxide levels in air restrict plants' ability to absorb nutrients ... [downloaded 01/30/2017]. This article, quotes researcher, Johan Uddling (one of the authors of the Feng and others study) as saying that the study's findings are "unequivocal", which I find astonishing. Why am my astonished? -- The original article had no such tone of "unequivocal" about it! In fact the original article cited other studies that demonstrated the benefits of enhanced CO2 for plants. The original study continually tempered its statements in regard to such studies, never arriving at an "unequivocal" conclusion that in any way excluded these other studies from consideration.

I, therefore, wonder how one of the authors of the original study could make such a bold claim. I can only harbor suspicions that this particular author has a vested interest in confirming his own non-scientific conclusion about CO2, which ignores some of the very research he used in the study that he helped perform and falsely represent after the fact. I would be curious to know whether the other authors of the study agreed with Uddling.

Judging from a later, 2016 article by one of the other study authors, Tobias Rutting, Nitrogen mineralization, not N2 fixation alleviates progressive nitrogen limitation – Comment on “Processes regulating progressive nitrogen limitation under elevated carbon dioxide: a meta-analysis” by Liang et al., I would say that Uddling was NOT speaking for the other authors. At the time of this writing, Rutting's article is listed as "under review" for the journal, BIOGEOSCIENCES, the full text of which is located at ... [downloaded 01/30/2017].

Notice one of Rutting's concluding statements in that article:

  • In conclusion, several processes can contribute to prevent the development of a PNL [progressive nitrogen limitation] under elevated CO2.

Those Who Say CO2 Is Good

Picture by Public Policy Institute, Center for the Study of Carbon Dioxide and Global Change
Picture by Public Policy Institute, Center for the Study of Carbon Dioxide and Global Change

People who grow plants for a living or deal with people who grow plants for a living seem to be most qualified in rendering judgments as to the practical benefits of exposing plants to elevated levels of CO2. For example, consider information from The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), the government ministry responsible for food, agriculture and rural sectors of the Canadian province of Ontario. According to this organization's website at ... ...

  • Carbon dioxide (CO2) is an essential component of photosynthesis.
  • CO2 increases productivity through improved plant growth and vigor, as evidenced by such effects as earlier flowering, higher fruit yields, reduced bud abortion in roses, improved stem strength and flower size.
  • Growers, therefore, should regard CO2 as a nutrient.

A more exhaustive description of CO2 benefits is available from the Science and Public Policy Institute, Center for the Study of Carbon Dioxide and Global Change, THE MANY BENEFITS OF ATMOSPHERIC CO2 ENRICHMENT, [downloaded 01/31/2017]

After reading such sources as these, which note at least fifty-five positive effects, a person starts to wonder why so many people revere the voices of academicians and activists above the voices of farmers and other professional plant growers. I can only say that I respect the voices of people who have their hands in the dirt and actually touch the plants day in and day out.

Seeing Is Believing


In my own exploration of CO2 plant fertilization, I have seen a continuing, disturbing pattern where intelligent people avoid reality, in order to nurture unfounded fears or to bolster preferred ideals. These intelligent people try extra hard to find the negative effects of CO2, going to extremes of mental gymnastics and verbal acrobatics to avoid considering the positive effects. I am forced, therefore, to distance myself from the deficiencies of such reasoning.

As a result, I arrive at the conclusion that more CO2 is good for plants. Any possible negative effects can be mediated by intelligent farming practices, intelligent land management, and intelligent plant breeding, ... all of which seem to be happening anyway, at least among many of those people engaged in the hands-on production of or management of plants.


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