Teaching about the Sun's energy is supported by five key concepts:a. Sunlight reaching Earth can heat the land, ocean, and atmosphere. Some of that sunlight is reflected back to space by the surface, clouds, or ice. Much of the sunlight that reaches Earth is absorbed and warms the planet.
b. When Earth emits the same amount of energy as it absorbs, its energy budget is in balance, and its average temperature remains stable.
c. The tilt of Earth's axis relative to its orbit around the sun results in predictable changes in the duration of daylight and the amount of sunlight received at any latitude throughout a year. These changes cause the annual cycle of seasons and associated temperature changes.
d. Gradual changes in Earth's rotation and orbit around the sun change the intensity of sunlight received in our planet's polar and equatorial regions. For at least the last 1 million years, these changes occurred in 100,000-year cycles that produced ice ages and the shorter warm periods between them.
e. A significant increase or decrease in the sun's energy output would cause Earth to warm or cool. Satellite measurements taken over the past 30 years show that the sun's energy output has changed only slightly and in both directions. These changes in the sun's energy are thought to be too small to be the cause of the recent warming observed on Earth.
The Sun's energy drives the climate system
The sun warms the planet, drives the hydrologic cycle, and makes life on Earth possible. The amount of sunlight received on Earth's surface is affected by the reflectivity of the surface, the angle of the sun, the output of the sun, and the cyclic variations of Earth's orbit around the sun.
The basic science of solar energy and the role it plays for Earth's climate can be understood by middle school students, but the complexities of the Earth's energy balance remains an area of active scientific research. Thus, this topic is both elemental and complex.
This principle is related to Energy Literacy Principle 2: Physical processes on Earth are the result of energy flow through the Earth system.
Show students the basic mechanics of the climate system
Understanding the role of solar radiation in the Earth's climate system can help us grasp important concepts such as:
The causes of the seasons.×
Seasons are caused by the tilt of Earth's axis. The tilted axis means that the northern and southern parts of Earth do not receive equal amounts of solar radiation (energy per unit area). When the southern hemisphere is tilted toward the sun, it is summer in the southern hemisphere and winter in the northern hemisphere. (Principle 1c)
The reasons ice ages occur.The ice ages were caused by changes in the distribution of solar radiation received over Earth's surface. The path of Earth's orbit is not constant. Variations in Earth's orbital path causes the solar radiation reaching any point on Earth's surface to change. (Principle 1d)
How the amount of energy emitted from the sun (sun's luminosity) changes over time.The sun's output is not constant. Its luminosity (total energy emitted by the sun) has increased over geologic time, and varies slightly over shorter time scales.
Why recent climate warming has not been caused by increases in the sun's energy output.The sun's energy output has not changed enough over the last decades to account for the increases in temperatures that have been observed during this same time. (Principle 1e)
Most forms of energy that humans use are derived from solar energy.Many forms of energy that humans use ultimately derive from solar radiation, such as food, hydrocarbons (such as oil and natural gas), wind energy, hydroelectric power, and of course, solar energy.
Helping students understand these ideas
Moreover, students of all ages, including college students and adults, have difficulty understanding what causes the seasons. In addition to the axial tilt, factors that come into play in people's mental models include the belief that Earth orbits the sun in an elongated elliptical path; confusion about the relative size, motion, and distance of the earth from the sun; how light travels; the length of Earth's revolution around the sun; and even the period of rotation. One strategy to mitigate this common misconception is to ensure that the "reasons for the seasons" are adequately addressed in high school, when students have sufficient background in geometry and physics to grasp the concepts (McCaffrey & Buhr, 2008).
Excellent explanations for this can be found at Skeptical Science: Sun and Climate: Moving in Opposite Directions and with a graphic from Bloomberg: What's Really Warming the World? This engaging graph is made with NASA data and model output.
Bringing these ideas into your classroom
Solar radiation is the fundamental energy driving our climate system, and nearly all climatic and biologic processes on Earth are dependent on solar input. Energy from the sun is essential for many processes on Earth including warming of the surface, evaporation, photosynthesis and atmospheric circulation. Thus, examining how the sun fuels different processes on Earth can be a part of many types of science courses. Many of the science concepts relating to this principle can be addressed by encouraging seasonal observations, participating in citizen science programs with students (such as GLOBE), and periodically revisiting the basics of how the amount and intensity of solar energy affects Earth's climate.
The ways that the Sun's energy drives the climate system can be taught from a very basic level on upward through the most sophisticated scientific approaches.Integrating Solutions - The science concepts that relate to solar radiation can be expanded to include solar energy engineering and technology, including solar ovens, passive solar design, solar thermal energy and solar electricity. This can help raise awareness for alternatives to the use of fossil fuel and create a forum for discussions about solutions to climate change that our society can adopt.
Teaching materials from the CLEAN collection
- Globes and other physical models can be used to show the tilt of Earth's axis and how that affects the distribution of sunlight during different seasons, such as in My Angle on Cooling: Effects of Distance and Inclination.
- Introduction to Earth's Climate - This lesson is an introduction to Earth's climate and covers key principles regarding Earth's unique climate, atmosphere, and regional and temporal climate differences.
- Feeling adventuresome? The activity Earth's Albedo uses popcorn kernels to simulate albedo in different regions of the Earth, while Amazing Albedo is a hands-on activity that involves measuring the temperature of different colored surfaces.
- The Climate: A Balancing Act applet allows students to adjust parameters that affect Earth's energy balance: incoming solar radiation, the albedo effect, the greenhouse effect, and outgoing radiation.
- Students can learn how orbital cycles and ice ages are well correlated with the Milankovitch Cycles Climate Applet.
- This Seasons Interactive visualization tool can become the basis for open-ended exploration of how solar radiation varies with location and season.
- The Solar Influence: Climate Change video from the National Academies can help reinforce the evidence that solar activity is not causing global warming.
Earth's Heat Budget is a hands-on laboratory activity that investigates the effects of distance and angle on the input of solar radiation, albedo, the heat capacity of land and water, and how these cause the seasons.
Motions of the Sun Lab uses an animated simulator to enable students to manipulate variables to understand the apparent motion of the sun in the sky.
- Observe changes in Earth's orbit that contribute to climate change - This animated visualization of Milankovitch cycles can set the stage for more advanced discussion of climate forcings.
- A quantitative approach can be used with this step-by-step introduction to a simple STELLA model: Modeling Earth's Energy Balance.
- Modeling Early Earth Climate with GEEBITT helps students become more familiar with the physical processes that made Earth's early climate so different from that of today.
Find activities and visuals for teaching this topic
What's Really Warming the World? - This animated graphic compares different forcings that are acting on Earth's climate. Climatic changes caused by orbital variation, the sun's luminosity, and volcanic emissions are compared with the effect of greenhouse emissions. The graphic is very engaging and the data is from NASA's Goddard Institute for Space Studies (GISS).
McCaffrey & Buhr, 2008: Clarifying Climate Confusion. - Journal article from Physical Geography about common misconceptions in climate science.
How do we teach about questions with no certain answers? - from a faculty workshop on teaching about the early Earth.
Earth's energy balance since 1950 - brief summary of a recent research article from Physics Today.