“I Get It Now”

Teaching the Physics of Climate Change

By Elissa Levy

Illustrator: Sawsan Chalabi

“Wait a minute,” said Sofia. Basically, we’re saying that every greenhouse effect diagram I can find on Google is either confusing or misleading.”

“Um, yeah,” replied Deiondre.

“Yeesh. Then how are people supposed to figure out how climate change works to understand how big this problem is?” asked Genelle.

“I guess you need to actually think about it. It makes sense if you think about it, but you have to put the pieces together yourself,” said Emiliano.

This conversation took place among my 9th-grade physics students at the High School for Climate Justice in East Harlem, New York. Climate change is one of the biggest existential threats to life on Earth. It is caused by greenhouse gas emissions, which are overwhelmingly generated by people with privilege. Marginalized communities disproportionately feel the effects. My students are predominantly Black and Latine. Some of my students are climate refugees, which they usually don’t realize until they arrive at our school. A student once stopped herself in the middle of a story about how her family immigrated to the United States from Bangladesh. She was talking about increasing heat and droughts that made it harder to get food and then remarked, “Aren’t these droughts because of climate change? Doesn’t that make me a climate refugee?” Another student from Central America told me, “The hurricanes got worse and the flooding got worse, so we moved to New York and now we’re here.” 

Climate change is global, but it’s also close to home for my students in East Harlem.

This past year, I used climate change as an anchoring phenomenon for my physics classes’ energy unit. I posed a key question: How has the average global temperature changed over the past 100 years, and what is driving this change? Indeed, most adults cannot answer this question. Youth need to understand the science so they can detect climate misinformation and then actively combat climate disinformation, perpetuated by people with extreme power whose near-term profits shrink when we address the climate crisis. For my students to become climate champions, they need their own mental models of anthropogenic climate change: what it is, how it happens, and what we need to do to fix it. I engage students in this exploration by creating space for asking questions, making meaning, and taking nobody’s word for it.

Planning the Unit     

When I began to plan this climate physics unit, I wrote a description of how it should feel for students to engage in this work. I wanted students to drive the meaning-making, using logic and data to develop their models of the climate rather than accepting synthesized texts. With such complex and nuanced concepts, they needed to collaborate, raising and exploring their questions together. They also needed to feel safe raising concerns such as “My mother works in the coal industry; does that make her a bad person?” “My grandparents don’t believe in climate change; who am I supposed to believe?” or “Is it ethically wrong to have kids on a planet that we’re destroying?” These questions are both moral and emotional. 

In general, scientists try to figure out what’s happening in our world by collecting data and creating models, so that we can design solutions to heal the world. All people are affected by science on both personal and communal levels. I needed my climate physics class to feel not like clean, cold calculation but rather like the heated, messy engagement that science really is.

Constructing Mental Models of Climate Change

There are many resources to help teachers understand climate change and how to teach it. In particular, I consulted Miseducation: How Climate Change Is Taught in America by Katie Worth, The Physics of Climate Change by Lawrence Krauss, and Physics: The First Science (chapter 14) by Peter Lindenfeld and Suzanne White Brahmia. I also watched videos from PBS and read articles from science and education journals. Although these resources are incredible, they all explain climate change and how it’s taught, rather than provide a structure for students to learn about the science of climate change. Guided by my research, I constructed the following arc for students to follow, so they could construct an explanation of how our planet is warming and begin to determine what we can do about it.

The sun gives us light energy. The first step in explaining the trend in average global temperature is to understand the role of the sun. I asked students, “What type of energy do we get from the sun?” Most of them said light and heat, which is what we’re commonly taught. I asked, “What does it mean for something to have heat energy? What is hotness?” 

I showed students two beakers, one with hot water in it and one with cold water in it. I put a drop of food coloring into each beaker, and students watched the color spread faster in the beaker with hot water. “What is hotness?” I asked again. “It’s when the material is shaking faster and making the particles inside it jiggle more,” they answered. With this definition of heat, I asked whether we can get heat from the sun. “No,” one student replied, “because we don’t get matter — stuff — from the sun, only light.”

The sun’s infrared light produces heat when it interacts with matter. After concluding that the energy coming from the sun is entirely light energy, I said, “Clearly there is a relationship between light and heat. What is that relationship?” 

Students came up with their own examples of light turning into thermal energy, such as pavement heating up when the sun is out. My favorite student question during this part of the unit was “Why is it that sometimes light doesn’t create heat, like an LED bulb or my cell phone screen, and other times light does create heat, like a match or an incandescent bulb?” My students already knew the law of conservation of energy, which says that energy can change its form and its location but cannot be created or destroyed. So I was delighted when my students identified a seeming paradox, which is that sometimes light produces a lot of heat and sometimes not so much.

The resolution to this conundrum lies in understanding infrared light as a mechanism of heat transfer. My students needed to understand first that there are wavelengths of light that our eyes can’t detect (infrared being the most relevant here) and then that infrared light transports heat. To bring students to this conclusion, I asked them, “What does a camera detect?” “Well, light, of course,” replied one student.  I showed students my TV remote control and started pressing random buttons. I asked students if they saw any light coming out of the remote; they did not. I held the remote control up to my cell phone camera, and students could clearly see light coming out of the remote! I asked students to give me a thumbs-up if they believed there are types of light that a camera can detect but we can’t see, and a thumbs-down otherwise. Every student gave a thumbs-up.     

In their groups, I asked students to use Google to learn about different types of cameras, including infrared cameras. One group of students explained it this way: “Light can have any wavelength, except we can only see some of them — about 400 to 700 nanometers. Infrared has a longer wavelength than we can see.”

Hot objects radiate infrared light. I showed students images of various objects (a person, a dog, a snake, a table, an ice cube) as viewed through an infrared camera. They kept track of which objects glowed brighter and which were dimmer. “Hotter things are brighter on an infrared camera,” one student pointed out. “People glow really brightly in infrared wavelengths, even in the dark. I wonder if incandescent bulbs glow much brighter than LED bulbs on an infrared camera, because infrared bulbs are hotter.” It was a spot-on prediction. One student asked, “Is that how the sun warms the earth?”

Some substances absorb infrared light and heat up as a result. I asked students to think about visible light. They knew from earlier science classes that when light hits an object, it can be reflected or absorbed. Since infrared light is still light, it should work the same way — the question is what happens to infrared light when it’s absorbed. Since students had already learned that hotter objects have faster-moving particles, they were able to infer that the absorption of infrared light causes particles to move faster and thus get hotter. Given what they knew about absorption and reflection, I asked each group of students to create a diagram showing the flow of infrared light from the sun to and within our planet. Every group approached the exercise in a slightly different way, but they all ultimately showed that some of the infrared light is absorbed by the earth and some of it goes out to space.     

Then I asked, “Looking at your diagram, what factors will change the fraction of infrared light that gets absorbed by the atmosphere instead of going out to space?” One student suggested that maybe different components of air might absorb different amounts of infrared light.

Greenhouse gases (especially carbon dioxide) heat up faster. I told students, “Let’s try comparing carbon dioxide in particular to a regular sample of air. What experiment could you design to see if carbon dioxide absorbs more or less infrared light than regular air?” Most students suggested we get two jars, one with air (which is a mixture of gases, including some carbon dioxide) and the other with pure carbon dioxide. One student explained, “Let’s put the jars in sunlight for a while and measure the temperature of the air inside. I think the glass with carbon dioxide will be hotter.” Alas, we didn’t actually do the experiment because we didn’t have pure carbon dioxide handy, but I do plan to do it in the future.

Instead of doing the experiment, we spent a class period reading together Eunice Foote’s 1856 paper “Circumstances Affecting the Heat of the Sun’s Rays,” where she did this experiment with carbon dioxide and air and concluded, “the receiver containing that [carbon dioxide] gas became itself much heated. . . . An atmosphere of that gas would give to our earth a high temperature.” Most people have never heard of Eunice Foote, whose groundbreaking work preceded all the commonly seen citations for the effects of carbon dioxide in the atmosphere. I asked students if they had thoughts on why people haven’t heard of her, and they surmised that it’s because of sexism. One student ventured that the greenhouse effect would be called the Foote Effect if Foote were male. Sexism has slowed scientific progress. I need my students to know this so they can be part of the solution.

After confirming that pure carbon dioxide gas heats up faster than air, I asked students to think about something that’s already hot. “Does it stay hot forever, or does it cool down?” I asked. They considered it obvious that hot things cool down, but they didn’t know how. The thermal energy must be going somewhere, but where? I showed them the PBS video Global Warming: Carbon Dioxide and the Greenhouse Effect. Any object whose temperature exceeds that of its surroundings will radiate infrared light, and the object will cool down in the process. Humans don’t cool down because the chemical reactions in our bodies generate new heat to replace the heat that is constantly radiating from us.

I paused the video and asked students to discuss in pairs: When they pump carbon dioxide into the transparent tube between the person and the infrared camera, what will happen to the image of the person on the camera? Answers varied. One student said, “It’ll get brighter!” Another student exclaimed, “It’ll disappear!” A third said, “I think nothing will change.” I love it when my students’ predictions (and reasons) differ. Sometimes students’ predictions are confirmed, and sometimes they’re disconfirmed, but predictions generate excitement about learning why things happen the way they do.

As the video progressed, students watched the person disappear from the camera image: Although the person emitted more infrared light than their surroundings, because the person was hotter than their surroundings, this infrared light was absorbed by the carbon dioxide and never made it to the infrared camera. One student asked, “So if I wanted to be invisible in the dark, even to someone with night vision goggles, then I need to walk around with a layer of carbon dioxide all around me?” “I think that might work,” I told him. 

More carbon dioxide in the air will make the planet hotter overall. As students discussed the implications of this experiment with their groups, the classroom got louder. A few students connected the law of conservation of energy with the presence of carbon dioxide in the atmosphere. One student put it this way: “If something on the earth is hot, and it has infrared light coming out of it, then that energy could go to outer space, right? But not if the carbon dioxide in the air absorbs that energy before it gets a chance to go to outer space?” 

Right. By this point in our unit, students were familiar with this style of questioning and model building, and they extended this conversation on their own initiative. “But then hold on,” said another student. “I thought we were putting a lot of carbon dioxide in the air by burning fossil fuels. So if there’s more carbon dioxide in the air, then there’s more infrared light getting absorbed, and the carbon dioxide will make the air hotter by absorbing all that energy that would otherwise have gone to outer space. Is that right?”

Yes, that’s right. Now my students can see what we’re up against with global warming.

Applying Understanding Toward Justice     

As students finished exploring the scientific principles behind climate change, I began to hear them express climate anxiety. 

“We’re not going to be OK, are we?” one student asked. “I don’t want to live in the world we’re making.” Another student had been reading climate fiction like Parable of the Sower by Octavia E. Butler, for English class, and Ship Breaker by Paolo Bacigalupi, on her own. “I thought these worlds were fake,” she said, “but maybe they’re the real future.”                         

One of the advantages of teaching where the entire school has a climate justice focus is that no single class has to shoulder the burden of teaching everything there is to teach about the climate crisis. All of my students were also enrolled in a yearlong climate justice seminar with my colleague Ben Otto. In the climate justice seminar, students go deeper into the human activities that produce the heat-trapping gases they learn about in physics class. They learn about the role of fossil fuels in colonization and the rise of capitalism, which created a system that benefits those in power while jeopardizing our planet. They also learn about the social movements addressing the crisis and how young people like them are making a difference.

We need our students to be part of the solution; the last part of my physics unit is about how they can make a difference themselves. Armed with a deeper understanding of the science, a few of my students contacted their congresspeople to explain why they need to champion climate legislation. I hope to see my students at climate protests. I hope to see them supporting products made with renewable energy and buying from companies that are carbon neutral. I hope they have learned enough to question the claims they see online and not fall for greenwashing. The more they understand the science, the more effective they will be as climate-minded citizens.

My students’ responses to these learning experiences were heartening. “I had always thought that climate change was because people don’t recycle,” one student told me. “But I get it now.” 

Elissa Levy (@elissadunnlevy) is a physics teacher and professional development facilitator in New York City. After a first career in the finance industry, she spent five years teaching at the High School for Climate Justice and now teaches at Hunter College High School.

Illustrator Sawsan Chalabi’s work can be seen at schalabi.com.