Exploring heat transfer on Earth’s surfaces

What types of light does the Sun emit? What types of light have the most energy? How does the Sun's energy transfer make the Earth's surface warmer, and how do different surface features (like ice, forests, water, rock) and human actions affect this heating process?

Light from the Sun is the primary source of energy on Earth. Sunlight is a form of electromagnetic radiation that carries energy from the Sun to Earth. When this energy reaches Earth’s atmosphere and surface, it can be absorbed, reflected, or transmitted depending on the properties of the material it encounters. The portion of sunlight we can see, visible light, is only a small part of the electromagnetic spectrum. This spectrum also includes infrared (IR) and ultraviolet (UV) light. Visible light has wavelengths of roughly 400 to 700 nanometers, while infrared light has longer wavelengths that we sense as heat.

Surface temperature can be observed using the electromagnetic spectrum. Every object emits electromagnetic energy according to its temperature. Hot objects emit shorter wavelength (higher) energy, while cooler objects emit longer wavelength (lower) energy. An Infrared Thermometer (IRT) can help measure the emitted energy from Earth’s surface. (Also see: Climatepuzzles.org spectrum of the Sun vs. Earth.)

Absorbed light will cause the surface to heat up, i.e. the molecules that comprise the material will vibrate faster. Each material has its own response to this heat, which we call “specific heat capacity.” The specific heat capacity of water is one of the highest among common substances, because the hydrogen bonds between molecules require a lot of energy to break, allowing water to absorb and release large amounts of heat with minimal temperature change. This property plays a crucial role in regulating Earth’s climate, stabilizing temperatures in living organisms and widely used in industrial cooling systems.

As the temperature of water increases and the molecules vibrate faster, the water, like all materials, will expand in size. This is called “thermal expansion.” Thermal expansion of the oceans is responsible for approximately half of observed sea level rise. The other half is from melting land ice that runs off into the ocean. See this JPL Sea Level Rise activity - “The total amount of water on Earth isn't increasing, but the volume of liquid that fills the ocean basins is growing, raising the elevation of the sea's surface and spilling ocean water onto low-lying land.” (Note: You can see NASA’s Sea Level Prediction Tool and NOAA’s Sea Level Rise Viewer to explore how this may impact your area and others).

The ways we experience heat and temperature, and the extent to which future sea level rise occurs, is largely dependent on how Earth’s various surfaces absorb heat and the impacts of humans on those surfaces. For example, the bright white ice caps help to reflect the Sun’s light back to space. If the ice melts, where will that energy go? Forests help to scatter light and reflect some of it back to space. What happens when forests are cut down? Concrete and asphalt absorb heat. What happens when we pave more of our landscape? The “urban heat island” effect arises when urban surfaces such as concrete, asphalt, and buildings absorb and retain more solar radiation than natural landscapes like vegetation and soil, which reflect more sunlight and cool through evapotranspiration.

Because Earth systems are all connected, changing one will have impacts on others, which can then amplify or reduce the overall impact. This is the idea of a “feedback loop.” For example, more heat absorption in the oceans will cause more water evaporation. Because water vapor is a greenhouse gas, it will also cause more heat to be retained in Earth’s atmosphere. More heat in the atmosphere will then further warm the oceans, amplifying the cycle – this is an example of a “positive feedback loop.” Alternatively, more heat absorption in oceans causing more evaporation can also result in more cloud cover, which will reflect more sunlight and reduce heat absorption, an example of a “negative feedback loop.” The long-term stability of Earth’s surface temperature depends on balancing heat transfer among different Earth systems.

You may want to precede this lesson set with: States of Matter and Particle Motion.

Real-world connections

• Sign up for Physicists To-Go to have a scientist talk to your students.
• Have students read and reflect on this year’s scientist profile on Eunice Newton Foote.
• See if you can brainstorm how these physics concepts relate to the United Nations Sustainable Development Goals
• Be a citizen scientist and contribute your temperature field data to the GLOBE database

Career Connections

• Explore Careers, US Bureau of Labor Statistics
• BLS Career Resources PDF
• Career One Stop - Interactive career exploration

Suggestions for drawing, illustrating, presenting content in creative ways

• Have students complete this Beat the Heat Urban Island Gizmo or this Protecting Permafrost - Heat Transfer STEM Lab Gizmo

Engineering and design challenges connected to the content

• Try out the educational experiment “What’s Causing Sea-Level Rise? Land Ice Vs. Sea Ice”
• Try out the educational activity “Sustainable Cities: Nature Based Solutions in Urban Design: Lesson Plan | Nature Lab”