Bigger isn’t always better. Too much of a good thing can be bad.

Many anti-environmentalists throw these simple truths to the wind, along with caution.

You can see it in the deceitful realm of climate change denial. It’s difficult to keep up with the constantly shifting — and debunked — denier arguments, but one common thread promoted by the likes of the U.S.-based Heartland Institute and its Canadian affiliate, the misnamed International Climate Science Coalition, illustrates the point. They claim carbon dioxide is good for plants, and plants are good for people, so we should aim to pump even more CO2 into the atmosphere than we already are.

We’ve examined the logical failings of this argument before — noting that studies have found not all plants benefit from increased CO2 and that most plants don’t fare well under climate change-exacerbated drought or flooding, among other facts. Emerging research should put the false notion to rest for good.

Several studies have found that, even when increased CO2 makes plants grow bigger and faster, it reduces proteins and other nutrients and increases carbohydrates in about 95 per cent of plant species, including important food crops such as barley, rice, wheat and potatoes. A 2014 Harvard School of Public Health study, published in Nature, looked at 130 species of food plants and found that increased CO2 reduced the amount of valuable minerals such as zinc and iron in all of them.

Another study, by Irakli Loladze at the Catholic University of Daegu in South Korea, looked at 130 species of food plants and found increased CO2 caused calcium, magnesium, potassium, zinc and iron concentrations in plants to decline by an average of eight per cent, while sugar and starch content increased.

As a Scientific American article points out, billions of people depend on crops like wheat and rice for iron and zinc. Zinc deficiency is linked to hundreds of thousands of deaths, mostly children, and exacerbates health issues such as pneumonia and malaria. Iron deficiency, which causes anemia, is responsible for one-fifth of maternal deaths worldwide.

Part of the problem with the industrial agricultural mindset and the denier argument that CO2 is plant food or “aerial fertilizer” is the idea that bigger and faster are better. These studies illustrate the problem with the climate change–denial argument but, in its pursuit of profit, industrial agriculture has often made the same mistake. Plants — and now even animals like salmon — have mainly been bred, through conventional breeding and genetic engineering, to grow faster and bigger, with little regard for nutrient value (leaving aside anomalies like the not-entirely-successful “golden rice”). But higher yields have often resulted in less nutritious fruits and vegetables.

Genetic engineering’s promise was increased yields and reduced need for pesticides, but studies show it has fallen far short of that ambition. A 2016 National Academy of Sciences study, as well as a New York Times investigation, found no evidence that genetically engineered crops increased yields over conventional crops. Although insecticide and fungicide use on GE crops in the U.S. and Canada has decreased, herbicide use has gone up to the point that overall pesticide use has increased. France, which doesn’t rely on genetically modified crops, has reduced use of all pesticides — 65 per cent for insecticides and fungicides and 36 per cent for herbicides — without any decrease in yields.

The “golden rice” experiment shows that plants can be engineered for higher nutrient value, but that hasn’t been the priority for large agrochemical companies.

As for carbon dioxide, we know that fossil fuel use, industrial agriculture, cement production and destruction of carbon sinks like wetlands and forests are driving recent global warming, to the detriment of humanity. The one flimsy argument climate change deniers have been holding onto — that it will make plants grow faster and bigger — has proven to be a poor one.

Like life itself, science is complex. Reductive strategies that look at phenomena and reactions in isolation miss the big picture. Our species faces an existential crisis. Overcoming it will require greater wisdom and knowledge and a better understanding of nature’s interconnectedness.

Tackling climate disruption and feeding humanity are connected. It’s past time to ignore the deniers, reassess our priorities and take the necessary measures to slow global warming.

— written with contributions from David Suzuki Foundation senior editor Ian Hanington.

Editor's note: A correction was made to this article at 1 p.m. Eastern Time on Thurs. Sept. 21, 2017 to update a misquoted study.

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Same arguments have been made by climate deniers regarding the effects of increased CO2 on tree growth: "In a global dendrochronological analysis, Gedalof and Berg (2010) also found little evidence for direct CO2 fertilization. Where increasing growth rates have been detected in boreal forests, many of these often have alternative explanations, including longer growing seasons and increased moisture availability, rather than direct effects of CO2 fertilization (e.g., Girardin et al.2011). In summary, little evidence exists of any significant increase in wood production in response to past increases in CO2, and hence it seems unlikely that future combinations of greatly increased CO2 and generally warmer conditions will stimulate major increases in the productivity of woody biomass by the tree species found in the present-day boreal forest.
Moreover, the increased capacity of boreal forests to sequester atmospheric CO2 is likely to be outweighed by the greatly increased losses of GHGs resulting from accelerated decomposition of organic matter in soils, litter, peat, and degrading permafrost and the near certainty of increased losses (in biomass, carbon, and wood volume) where drought, fires, and other disturbances are increasing and recurrent."
(source: NRC Research Press, October 09, 2013: "Anticipating the consequences of climate change for Canada's boreal forest ecosystems")"
"For the past century, Canada's managed forests have been a significant carbon sink, steadily adding carbon to that already stored. In recent decades, however, the situation has reversed in some years: Canada's forests have become carbon sources, releasing more carbon into the atmosphere than they are accumulating in any given year."
Under the Kyoto Protocol, Canada had the obligation to report all emissions (resulting or not from human activities), from Canada's managed forests which cover 2/3 of Canada's forests. As GHG emissions from that sector (LULUCF) were increasing substantially over the years as a result of "natural disturbances" (e.g. wildfires, insect infestations such as the mountain pine beetle), the Harper administration (after dropping out of Kyoto) decided "not to include" emissions from the LULUCF sector in its annual report to the UNFCCC.
(source: Ontario Ministry of Natural Resources, climate change research report CCRR-20: "Climate Change, Carbon Sequestration and Forest Fire Protection in the Canadian Boreal Zone" - Greenhouse Gas emissions Accounting and the Forest Sector)
In its 2016 report to the UNFCCC (section 5.1 footnote), the Trudeau administration went even further by denying the effects of climate change on natural disturbances: "Canada has indicated that is accounting for managed forests towards its emissions reductions target will exclude the impacts of natural disturbances because these impacts are non-anthropogenic."
On the other hand, the present administration (contrary to the precedent administration) has decided to include some statistics in the LULUCF sector that "if included" would reduce Canada's total GHG emissions. They (the politicians who hold power) realized that adding "real" emissions from "natural disturbances" would result in the impossibility for Canada to reach its emissions reductions target, and that would be politically damaging.

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