Scientist-like persons hired by the fossil fuel industry have long maintained we should celebrate an ever-increasing level of carbon dioxide in our atmosphere. This gas, a key building block in the photosynthetic process, can enable plants to grow faster and get larger. It’s been called the “CO 2 fertilization effect.” Many crop yields are projected to increase. And bigger woody plants, the reasoning goes, can amass more carbon, thus helping to slow the rate of CO 2 increase in a handy negative-feedback loop.
In other words, they argue that climate change is good for plants, which in turn will help curb climate change. It’s an elegant win-win situation, and environmentalists no longer have to lose sleep over skyrocketing carbon dioxide. However, as with many supposed “truths,” this argument falls apart upon close examination. It’s like in 1981 when former President Ronald Reagan said “Trees cause more air pollution than automobiles do.” He was referring to terpenols (responsible for the pleasant piney-woods aroma in the forest), which can react with auto emissions to form ozone. In the larger picture, trees reduce air pollution of all sorts – and sequester carbon as well – on a colossal scale worldwide. His statement was “true” in a minor, technical sense for a single pollutant, but it was misleading, and for all intents and purposes, false.
In a similar vein, climate-change apologists have a kernel of truth here. Around 95% of plants on Earth can take advantage of more abundant carbon dioxide. In greenhouse trials, plants did indeed get larger when more CO 2 was pumped in. This would suggest that most food crops, with the exception of millet, sorghum, and a handful of others unable to use extra CO 2 , will be larger and possibly mature more quickly. Hooray! So far, so good for the petroleum lobby. Unfortunately, as CO 2 levels increase, the nutritional value of our food goes down the toilet. Dr. Samuel Myers, a Harvard University principal research scientist in environmental health, lays it out bluntly in a January 28, 2018 Scientific American article entitled “Ask the Experts: Does Rising CO 2 Benefit Plants?”
According to Dr. Myers, “We know unequivocally that when you grow food at elevated CO 2 levels in fields, it becomes less nutritious…[food crops] lose significant amounts of iron and zinc—and grains [also] lose protein.” While this correlation is well-established, it is not yet known just why nutrient leaching of crops happens as CO 2 spikes. Dr. Myers and his team assert that if atmospheric carbon dioxide reaches the predicted concentration of 550 parts per million by 2050, the nutritional value of major food staples could drop low enough to cause widespread health effects. He estimates that 300 million to 350 million more people, mainly in food-insecure regions, will become protein-deficient by mid-century as a result of crops’ diminished quality. In addition, as many as 1.4 billion women and small children will suffer anemia due to iron-depleted crops, all thanks to the highly touted CO 2 fertilizer effect.
Another well-documented and equally mysterious plant response to a profusion of carbon dioxide in the air is that plant leaves across all species thicken. The “fat-leaf effect” would be a mere curiosity, except that the thicker a plant’s leaves get, the less carbon it is able to sequester. Oops. On October 1, 2018, scientists at the University of Washington published a study on this phenomenon in the journal Global Biogeochemical Cycles. The researchers combined their previous leaf-thickness measurements on plants grown in elevated-CO 2 chambers with current global climate models. They calculate that beyond 2050, the world’s forests will have lost the capacity to store roughly 6.4 billion tons of carbon dioxide each year. To put it in perspective, that’s about one-fifth of yearly worldwide carbon emissions from fossil-fuel burning.
A weakened forest “carbon sink” needs to be incorporated into future climate modeling, say the University of Washington team who carried out the study. To throw another wet blanket on the rosy spin some would put on rising CO 2 , weather extremes become more common and intense as global temperatures shoot upwards. Floods, droughts, and even extended hot spells all strain our food supply. Plus, the CO 2 fertilizer effect appears to be self-limiting. Exactly to what extent it can boost plant growth, though, is ultimately not known. A somewhat related sidebar is that poison ivy seems especially good at using extra carbon dioxide to grow bigger faster. Not only that, it has recently come to light that its toxic urushiol oil gets increasingly potent as CO 2 numbers climb. I’m itching to find out if this unpleasant side effect of climate change helps convince a few oil-patch advocates to change sides.
Paul Hetzler is a former Cornell Cooperative Extension Educator. To help the planet, he tries not to exhale.