Do Plants Benefit From High CO₂ Levels?

Written By Teacher: Elizabeth Ward

My name is Elizabeth Ward. I am a former Early Childhood, Elementary, and English as a Foreign Language educator. I have taught third grade Science and Social Studies as well as Kindergarten in both urban and rural Oklahoma public schools. I taught online EFL to students of all ages in China for four years. I also have experience in curriculum development and content design for teachers in the physical and digital classroom. As a former teacher I have a passion for supporting teachers and making their jobs easier. I currently live in the greater Houston area with my husband and four dogs. 

The relationship between carbon dioxide levels and plant growth is more complex than it might initially seem. While plants need CO2 for photosynthesis, very high levels can disrupt ecosystems and have unintended consequences. Exploring this topic helps students understand the nuanced interactions between environmental factors and plant life, connecting climate science to biology. Resources like experiments, data analysis, and case studies can help students critically evaluate the benefits and limits of increased CO2 on plants and ecosystems. Invite high school students to learn about the flow of energy through ecosystems with this video from Khan Academy. Even younger students can explore this topic! Consider this Life in Soil Science Lesson where young students can learn about carbon sinks. 

Written By: MIT Environmental Solutions Initiative

The MIT Climate Change Engagement Program, a part of MIT Climate HQ, provides the public with nonpartisan, easy-to-understand, and scientifically-grounded information on climate change and its solutions.

It’s true that plants love CO2. During photosynthesis, they take in carbon dioxide and, with the assistance of water and sunlight, make energy for themselves while releasing oxygen for us to breathe. Plants have been around for billions of years and have lived on Earth at times when the planet had far more CO2 in the air than it does now. So, would plants prefer a more carbon-heavy planet, like the one humans are now creating with our greenhouse gas emissions?

Not necessarily, says David Des Marais, an MIT Professor of Civil and Environmental Engineering who studies how plants respond to their environments. “The short answer,” Des Marais says, “is that most plants will grow faster and bigger with extra atmospheric CO2—all else being equal.” However, plant growth is too complex for a one-size-fits-all law like “more CO2 is better.”

Experiments in which scientists piped extra CO2 into plant-growing chambers have proven this basic science: the additional carbon makes plants grow faster if you maintain other factors, such as soil nutrient and water availability. Yet things may not be so simple for the planet at large, Des Marais says. Additional experiments have tracked plants growing in free air carbon enrichment (FACE) sites, where the researchers added CO2 not to enclosed chambers but to open environments such as agricultural fields that more closely simulate reality. Although the added carbon sped up plant growth in these places, it did not accelerate nearly as quickly as for plants in closed, CO2-rich chambers.

Although plants need carbon dioxide to grow, their success in very high-carbon environments is not guaranteed. Not all plants like extra carbon equally. And for those carbon aficionados in the plant kingdom, CO2 is not the only factor that controls growth. As any aspiring green thumb knows, plants need the right balance of water and soil nutrients to translate extra carbon dioxide into growth.