Yves here. The fact that more CO2 hurts the productivity of crops is probably old news to many readers, but this exposition may be helpful in discussing the impact with friends and family.
By Karin Kirk. Originally published at Yale Climate Connections
ake a look out the window and it’s easy to see how people are changing the landscape. The human fingerprint touches almost every part of the globe. We’ve also shaped the planet in ways that aren’t visible: Human activities have actually changed the composition of the atmosphere. Carbon dioxide (CO2) is an important component of the atmosphere, and human activities have increased the amount of this gas in the atmosphere by 45% since widespread industrial activities began in the mid-1700s.
This is important because CO2 plays multiple roles in keeping Earth’s climate stable. Nature is a carefully balanced system, and over the years, humans have disrupted this balance. Thankfully, we also are capable of reducing our impact – especially now that we understand more about how the Earth system works.
But you may have heard a myth that nature’s balance doesn’t really matter. After all, CO2 is natural, and it helps plants and crops grow. That’s true. But it’s also misleading in that it’s only part of the story. A widely circulated myth suggests that adding extra CO2 to the atmosphere will fertilize plants and crops and make the world greener and better. Unfortunately, that turns out not to be true.
The myth that CO2 is plant food and that “extra” CO2 therefore can’t be bad is an example of a logical fallacy. It sort of sounds right, but it’s a major oversimplification. It’s appealing because it suggests that it’s okay to emit the pollution that causes climate change. But the myth is not true. It’s so oversimplified that it leaves out other important factors that help plants grow – and all of the damage that extra CO2 is causing. Just think of it in terms of “too much of a good thing is a bad thing” as, for example, with too much water causing a bathtub to overflow.
Fertilizer Alone Does Not Make a Successful Garden
A lot of myths have a grain of truth to them. That’s part of what makes them believable – at first. But it’s up to us to look beyond that single fragment of a fact. In the case of the CO2-as-fertilizer myth, you can test the idea by thinking about your own garden. Is fertilizer alone sufficient to create a healthy garden? Of course not. A garden needs the right amount of water, stable weather conditions, and plants that are suited to the local environment. These are the same factors that have been disrupted by an overload of CO2 in the atmosphere. For example, just adding more fertilizer doesn’t help plants when a garden is getting either too much or not enough water.
CO2 Is Natural, But Can Also Be Harmful
Another facet to this myth is that CO2 is natural, so therefore it can’t be a bad thing. Again, a “gut check” can show how that logic doesn’t hold up to scrutiny. For example, nitrogen and phosphorus are also plant fertilizers, but they’re pollutants when there’s too much of them. An overdose of nitrogen or phosphorus triggers algae blooms, kills fish, and turns lakes into smelly swamps. Even oxygen is explosive in high concentrations. Many serious pollutants – mercury, lead, arsenic – are naturally occurring. But they’re still dangerous. The same holds true for CO2, and it’s both a natural, necessary substance and a pollutant in high concentrations.
It’s All About Balance
Nature is like a recipe, with each ingredient needed in just the right measure. A pinch of nutmeg gives pumpkin pie a rich, warm flavor, but a tablespoon of nutmeg would ruin the pie. A car’s engine runs on a precise blend of air, fuel, and spark. Overloading one element disrupts the whole system. Many aspects of nature operate in a similarly balanced way.
For example, the atmosphere has a specific recipe. CO2 and other greenhouse gases are an essential part of the recipe because they trap heat in the atmosphere. With no CO2 Planet Earth would be in a perpetual ice age. But a small amount of CO2 keeps the planet in the famous “Goldilocks and the Three Bears” condition: not too hot, not too cold, but the “just right” zone that’s ideal for life as we know it. Too much CO2 overheats the planet.
By studying Earth’s history, scientists have learned that when there was a lot of CO2 in the atmosphere, the planet was hot. In fact, the last time the Earth had as much CO2 in the atmosphere as it now does was the Pliocene Epoch, more than 3 million years ago. At that time, Earth’s atmosphere was 3.6 to 7.2 degrees Fahrenheit warmer (2 to 4 degrees Celsius) than it is today. And global sea level was 50 to 80 feet (15 to 25 meters) higher.
Climate Change Is Hard on Plants
The basics of climate change are actually easy to understand. Human activities emit around 100 million tonsof CO2 every day, mostly by burning fossil fuels, which causes the atmosphere to trap more heat. As a result of that heat-trapping pollution, the atmosphere, land, and oceans have all become warmer. The added heat triggers side effects like more intense rainstorms, floods, prolonged heat waves, and droughts. In turn, those unpleasant conditions lead to more frequent and severe wildfires, insect outbreaks, and crop failures. Sure, today’s plants have a bit more fertilizer from the extra CO2 in the air, but that additional CO2 causes many other problems, harming many plants and crops. Climate change is disrupting plant growth.
Agricultural Experiments Show Negative Effects
Scientists have performed many experiments to see what happens when plants and agricultural crops receive extra CO2. When supplemental CO2 was pumped into the air around plants, they grew faster. For this reason, CO2 is sometimes piped into enclosed greenhouses to boost production. But greenhouse plants also have optimal amounts of water, excellent soil, and controlled temperatures. It’s usually a different story out in the real world.
To conduct a more “real world” experiment, other studies have given plants extra CO2 plus an increase in temperature. In these conditions, many plants and crops grew poorly. In most cases, the boost from CO2 was overwhelmed by the hotter conditions. These experiments demonstrate that the myth of CO2 fertilization is false, and peer-reviewed reports find that major crops like wheat, rice, corn, and soybeans will become less productive as the world heats up.
Likewise, a landmark study in 2018 found that growing rice in high-CO2 conditions makes it less nutritious. As a basic grain, rice plays a critical role in feeding the world’s population. The extra CO2 caused an imbalance within the crop’s chemical makeup, which resulted in rice that had lower amounts of protein, iron, zinc, and B-vitamins. “The entire elemental balance is out of whack,” explained plant physiologist Lewis Ziska, an author of the study. This result is yet another example of how the recipe of nature is being disrupted by excess CO2.
Bad News Can Lead to Our Making Needed Changes
Myths that try to “disprove” climate change can be appealing. Nobody loves the idea that human-caused pollution is now altering the chemical balance of Earth’s atmosphere. Nevertheless, climate change is happening.
But we can use our improving knowledge to prevent these problems from getting worse and maintain a healthy climate for plants and people.