How Do Greenhouse Gases Trap Heat?

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. 

Greenhouse gases are a natural and essential part of Earth's atmosphere, but human activities have significantly increased their concentration, intensifying global warming. Understanding how these gases trap heat provides students with a foundational knowledge of the science behind climate change and its far-reaching impacts. Exploring this topic allows students to connect core scientific principles to pressing environmental challenges, fostering critical thinking about causes, consequences, and solutions. Explore this concept with younger students using The Greenhouse Effect Experiment from NJ Agriculture in the Classroom. High School students can investigate Greenhouse Gas Equivalencies with this calculator. 

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.

What do CO2, methane, and water vapor have in common? If your first thought was “greenhouse gases,” you’d be correct! Greenhouse gases trap heat in the atmosphere, in a process called the “greenhouse effect.” But how do these molecules actually warm our planet?

We’ll start our exploration of greenhouse gases with a single carbon dioxide (CO2) molecule. Let’s say this CO2 molecule came from the exhaust in your car. From your tailpipe, it drifts up into the atmosphere, diffusing among the other gases. There, particles of light—photons—hit our molecule.

So what happens to those photons? “Greenhouse gas molecules will absorb that light, causing the bonds between atoms to vibrate,” says Jesse Kroll, Professor of Civil and Environmental Engineering and Chemical Engineering at MIT. “This traps the energy, which would otherwise go back into space, and so has the effect of heating up the atmosphere.” Basically, the bonds between the carbon and oxygen atoms in our CO2 molecule bend and stretch to absorb photons. (With other greenhouse gases, the molecular bonds are different, but in all cases, they absorb photons, stopping them from leaving the atmosphere.)

Eventually, our CO2 molecule will release these photons. Sometimes, the photons continue out into space. But other times, they rebound back into the Earth’s atmosphere, where their heat remains trapped.