The physics of climate change

The United Nations has called climate change – the human-caused long-term shift in average temperature and weather conditions – the “defining issue of our time.” It’s one of the biggest challenges facing today’s students who are coming of age alongside the consequences of a warming Earth. 

Over the last 150 years, average atmospheric temperature has increased by more than 1 degree Celsius, ocean levels have risen by about 20 cm, glaciers are retreating across the globe, and polar ice is in decline. While our changing climate impacts life on Earth in increasingly complex ways, the science behind it has a surprisingly simple explanation: physics.

“At its core, climate change is about how much energy flows in and out of the Earth. Anytime you’re talking energy or heat, you’re talking physics,” says Dave Fish, Teacher in Residence at Perimeter Institute. 

Fish supports Perimeter’s Teacher Network, a program that equips teachers around the world with free tools and resources for teaching science. Like all of Perimeter’s teacher resources, Evidence for Climate Change is free, and was developed in partnership with high school teachers and University of Waterloo scientists. The resource explores the basic science behind climate change and offers a series of videos and hands-on experiments teachers can share with their students. Six years after launching, Fish says the resource remains popular, with more than 400 downloads in the past year. 

“These are resources that equip teachers, but they are free for anybody to download and learn at home, all designed and approved by teachers and Perimeter scientists,” says Fish. “In this resource, people can understand what’s going on when we talk about climate change through three simple lessons relating to physics.” 

Lesson 1: Molecules vibrate

Every day the Earth is bathed in radiant energy from the Sun. In basic terms, visible light hits the Earth, warms the surface, and re-emits infrared light, which humans feel as heat. In a perfect world, the heat from infrared light would leave the Earth, allowing for energy in, energy out. 

But human-caused carbon dioxide emissions have quadrupled since 1960. These increased emissions are compounded by deforestation, which reduces how much carbon dioxide is stored in the biosphere. A carbon dioxide molecule is made up of one carbon atom double-bonded to two oxygen atoms on each side. Classroom models of carbon dioxide often depict the double bonds as springs, to show they are in motion. 

“The vibration of molecules – and harmonic motion – are physics concepts. Since carbon dioxide vibrates at the same frequency as infrared light, it easily interrupts infrared energy that is leaving Earth and redirects it other directions, instead of letting it escape,” says Fish. 

Lesson 2: Heat transfer

It’s a basic law of thermodynamics that heat flows from hot to cold. Just as heat from a hot mug of tea will warm a cool hand, the heat that carbon dioxide retains in the air moves to the Earth’s oceans. Oceans have absorbed 90 percent of the excess heat trapped by increasing amounts of greenhouse gases.

“We have a demonstration in our climate change resource, where students hold a balloon over a flame, and if they put some water in the balloon, it won’t pop because the water absorbs the heat,” says Fish. “That’s a physics concept called ‘specific heat capacity’ that is covered in the Grade 11 curriculum, and it illustrates a part of the climate change story, that we are slowly warming up the oceans.” 

Fish says the balloon experiment is an accessible way for students to see for themselves that it takes more energy to heat water than air, and it helps them understand that most of the heat (thermal energy) gets absorbed by oceans. 

Lesson 3: Expansion

What happens when water heats up? It expands. As water molecules get warmer, they vibrate more and take up additional space. The thermal energy absorbed by the ocean leads to an increase in volume, causing sea levels to rise. 

Compounding this, melting land ice also causes sea levels to rise. 

“If you put ice in a drink, the water level rises. Similarly, when an iceberg falls into the ocean it causes a rise in sea level. Much of the ice we have on Earth is located on land, and as temperatures rise this ice melts and runs off into the ocean, causing sea levels to rise,” says Fish. 

The resource suggests a simple demonstration with two containers. One contains water with ice floating in it. The second contains water, rocks, and ice sitting on top. Students are tasked with monitoring water levels in both containers to track changes. 

A challenge for today’s students

“Through the teacher resources, we build a solid foundation of the story of climate change using just the physics, through the mechanism that heat is retained, the way heat transfers, and what happens when things get hot,” says Fish. He feels confident the resources tell an effective story through physics, but his team frequently gets follow-up questions from teachers who use it: “What do we do about climate change?”

Exactly. 

Fish hopes that as more of today’s students learn the science behind climate change, it will give them the foundation they need to consider solutions. 

“There’s so much opportunity for students to find ways to make current technologies more climate-friendly,” Fish says. “How do we make better solar panels, wind turbines, and hydroelectric plants? How can we extract energy out of the natural systems without creating pollution? Those solutions will also be rooted in physics.” 

Find the “Evidence for Climate Change” resource and try it yourself, along with dozens of other free lesson plans, on Perimeter’s teacher resources site.