Climate Change Teacher Guide

Unit

Climate Change

Subject

Physics

Grade Level

HS

Activity Name(s)

Energy Balance and Temperature 

Greenhouse Gases

Being Prepared

This activity is best done if every student has access to a computer. If this is not possible you can group students into groups of 2. This activity is entirely done on a computer as a simulation. It is ideal if you have a Win 7 or a newer version of Windows, but it will run on Win xP. If you have Mac computers you will need to update your Java and Adobe Flash.

Getting Started

There are no special sensors for this simulation

Suggested Timeline

It is suggested that the instructor allow 1.5 days for each activity with one day for discussion and debriefing.

Thinking about the Discovery Questions

This unit addresses the topic of Climate Change. Climate change as defined is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. Misconceptions may include students not knowing what environmental factors cause climate change, belief about its' cause by humans or is it a natural occurrence, controversy as to is the evidence presented for its' occurrence valid.

Activity 1

What happens when sunlight strikes Earth?

Energy is transferred to objects on, in and above the Earth

Activity 2

How does Earth's atmosphere affect the radiation energy balance?

As this infrared radiation emitted from earth's surface passes through the atmosphere on its way to space, some is absorbed, heating the planet. This heating process is called the greenhouse effect. The greenhouse effect has been crucial to maintaining earth's energy balance and temperature throughout its history, making the planet habitable. Recently, scientists have concluded that earth's energy system is out of balance, as increasing concentrations of greenhouse gases are causing additional energy to be absorbed.

Learning Objectives

NGSS

• Performance Expectations
  • HS-PS4-3. Evaluate the claims, evidence, and reasoning behind the idea that electromagnetic radiation can be described either by a wave model or a particle model, and that for some situations one model is more useful than the other.
  • HS-ESS2-2. Analyze geoscience data to make the claim that one change to Earth's surface can create feedbacks that cause changes to other Earth systems.
  • HS-ESS2-4. Use a model to describe how variations in the flow of energy into and out of Earth systems result in changes in climate.
  • HS-ESS3-6. Use a computational representation to illustrate the relationships among Earth systems and how those relationships are being modified due to human activity.
• Disciplinary Core Ideas
  • Earth Materials and Systems
    • Earth's systems, being dynamic and interacting, cause feedback effects that can increase or decrease the original changes.
    • The geological record shows that changes to global and regional climate can be caused by interactions among changes in the sun's energy output or Earth's orbit, tectonic events, ocean circulation, volcanic activity, glaciers, vegetation, and human activities. These changes can occur on a variety of time scales from sudden (e.g., volcanic ash clouds) to intermediate (ice ages) to very long-term tectonic cycles.
  • Earth and the Solar System
    • Cyclical changes in the shape of Earth's orbit around the sun, together with changes in the tilt of the planet's axis of rotation, both occurring over hundreds of thousands of years, have altered the intensity and distribution of sunlight falling on the earth. These phenomena cause a cycle of ice ages and other gradual climate changes.
  • Electromagnetic Radiation
    • When light or longer wavelength electromagnetic radiation is absorbed in matter, it is generally converted into thermal energy (heat). Shorter wavelength electromagnetic radiation (ultraviolet, X-rays, gamma rays) can ionize atoms and cause damage to living cells.
  • Global Climate Change
    • Human activities, such as the release of greenhouse gases from burning fossil fuels, are major factors in the current rise in Earth's mean surface temperature (global warming). Reducing the level of climate change and reducing human vulnerability to whatever climate changes do occur depend on the understanding of climate science, engineering capabilities, and other kinds of knowledge, such as understanding of human behavior and on applying that knowledge wisely in decisions and activities.
  • Weather and Climate
    • The foundation for Earth's global climate systems is the electromagnetic radiation from the sun, as well as its reflection, absorption, storage, and redistribution among the atmosphere, ocean, and land systems, and this energy's re-radiation into space.
    • Changes in the atmosphere due to human activity have increased carbon dioxide concentrations and thus affect climate.
    • Current models predict that, although future regional climate changes will be complex and varied, average global temperatures will continue to rise. The outcomes predicted by global climate models strongly depend on the amounts of human-generated greenhouse gases added to the atmosphere each year and by the ways in which these gases are absorbed by the ocean and biosphere.
• Practices
  • Analyzing and Interpreting Data
    • Analyze data using computational models in order to make valid and reliable scientific claims.
  • Constructing Explanations and Designing Solutions
    • Apply scientific reasoning to link evidence to the claims to assess the extent to which the reasoning and data support the explanation or conclusion.
  • Developing and Using Models
    • Use a model to provide mechanistic accounts of phenomena.
  • Science and Engineering Practices
    • Models, mechanisms, and explanations collectively serve as tools in the development of a scientific theory.
• Crosscutting Concepts
  • Cause and Effect
    • Empirical evidence is required to differentiate between cause and correlation and make claims about specific causes and effects.
    • Cause and effect relationships can be suggested and predicted for complex natural and human designed systems by examining what is known about smaller scale mechanisms within the system.
  • Energy and Matter
    • Energy drives the cycling of matter within and between systems.
  • Science Addresses Questions About the Natural and Material World
    • Science and technology may raise ethical issues for which science, by itself, does not provide answers and solutions.
    • Science knowledge indicates what can happen in natural systems—not what should happen. The latter involves ethics, values, and human decisions about the use of knowledge.
    • Many decisions are not made using science alone, but rely on social and cultural contexts to resolve issues.
  • Scientific Knowledge Assumes an Order and Consistency in Natural Systems
    • Scientific knowledge is based on the assumption that natural laws operate today as they did in the past and they will continue to do so in the future.
  • Stability and Change
    • Much of science deals with constructing explanations of how things change and how they remain stable.
    • Feedback (negative or positive) can stabilize or destabilize a system.
    • Change and rates of change can be quantified and modeled over very short or very long periods of time. Some system changes are irreversible.
  • Systems and System Models
    • When investigating or describing a system, the boundaries and initial conditions of the system need to be defined and their inputs and outputs analyzed and described using models.
    • Models (e.g., physical, mathematical, computer models) can be used to simulate systems and interactions—including energy, matter, and information flows—within and between systems at different scales.

NSES

• Chemical reactions may release or consume energy. Some reactions such as the burning fossil fuels release large amounts of energy by losing heat and by emitting light. Light can initiate many chemical reactions such as photosynthesis and the evolution of urban smog.
• Earth systems have internal and external sources of energy, both of which create heat. The sun is the major external source of energy. Two primary sources of internal energy are the decay of radioactive isotopes and the gravitational energy from the earth's original formation.
• Earth systems have internal and external sources of energy, both of which create heat. The sun is the major external source of energy. Two primary sources of internal energy are the decay of radioactive isotopes and the gravitational energy from the earth's original formation.
• Heating of earth's surface and atmosphere by the sun drives convection within the atmosphere and oceans, producing winds and ocean currents.
• Global climate is determined by energy transfer from the sun at and near the earth's surface. This energy transfer is influenced by dynamic processes such as cloud cover and the earth's rotation, and static conditions such as the position of mountain ranges and oceans.

Discussion: Setting the Stage

What Students Need to Know

1. Students need a basic knowledge of the composition of Earth's atmosphere. Without this foundation, it will be difficult to comprehend why greenhouse gas concentrations, which compose a tiny percentage of our atmosphere, can have a significant impact on global climate. 

The atmosphere is made up of molecular nitrogen (N2) and oxygen (O2), and a mixture of other gases. Nigrogen makes up approximately 78% of the atmosphere and oxygen 21%. The remaining 1% is made up of argon (Ar), carbon dioxide (CO2), helium (He), neon (Ne), krypton (Kt), xenon (Xe) and a small sliver of trace gases. One of these trace gases is ozone. (Text courtesy of Langley Research Center, NASA, Hampton, VA)

2. Students need to know what we mean by "Earth's Energy Budget". 

Earth's heat engine does more than simply move heat from one part of the surface to another. It also moves heat from the Earth's surface and lower atmosphere back to space. This flow of incoming and outgoing energy is Earth's energy budget. For Earth's temperature to be stable over long periods of time, incoming energy and outgoing energy have to be equal. About 29% of the solar energy that arrives at the top of the atmosphere is reflected back to space by clouds, atmospheric particles, or bright ground surfaces like sea ice and snow. This energy plays no role in Earth's climate system. About 23% of incoming solar energy is absorbed in the atmosphere by water vapor, dust, and ozone. About 48% passes through the atmosphere and is absorbed by the surface of Earth. The atmosphere and the surface of the Earth together absorb 71% of incoming solar radiation, so together, they must radiate that much energy back to space for the planet to maintain its energy balance. (Text courtesy of NASA Earth Observatory, Goddard Space Flight Center)

3. Students need a working definition of albedo. The European Space Agency (ESA) provides this definition: "The reflecting power of a surface is known as albedo. Bright snow and ice have a high albedo, meaning they reflect solar radiation back into space, while green areas like forests and fields have a much lower albedo. The lower the albedo, the more energy from the Sun is absorbed."

Activity 1

• Write down what you already know about radiation hitting Earth. List all of the physical features of the atmosphere and Earth's surface that might change this energy balance.

  Student answers will vary - some examples might include the layers of the atmosphere, features might include mountains, oceans, deserts, grasslands, glaciers. 

Activity 2

• What do you think "greenhouse gases" do? Explain how you think greenhouse gases affect light and infrared radiation in the atmosphere.

  Students should include in their answer phrases such as "carbon dioxide and methane prevent heat from escaping out of Earth's atmosphere into space". Teachers: Depending on students' prior knowledge, they may understand that certain molecules (such as carbon dioxide) absorb infrared radiation more strongly than others. When sunlight strikes the Earth, much of it is absorbed. Some is radiated back into the atmosphere as longer-wavelength infrared radiation. When infrared radiation strikes a greenhouse gas, it gets "trapped" and does not escape into space. The heat is released into Earth's atmosphere. Greenhouse gases are desirable to some extent -- without them, our planet would be a frigid, icy ball. But in recent years, the concentration of greenhouse gases (carbon dioxide, methane, nitrous oxide) has risen markedly. The more greenhouse gas molecules, the more infrared gets trapped in the atmosphere. This extra heat is a causing a rise in global temperature, effecting change such as polar ice cap melting, more frequent extreme weather events, and changes in the oceans.

Discussion: Formative Questions

Activity 1

• Does the temperature of Earth ever stay constant?

  No, temperatures are not constant on planet Earth, due to seasonal changes, Earth's axial tilt, changing regional weather patterns, ocean conditions, and many other factors.

• How much fluctuation (variation) in temperature is there? What affects the temperature?

  Many factors affect temperature variations on Earth, including latitude and altitude, cloud cover, surface conditions (for example, snow-covered ground reflects sunlight while bare ground absorbs much more light), ocean currents, day/night patterns, and regional weather patterns. 

Activity 2

• Can you figure out what happens when these rays hit a greenhouse gas molecule? Do light and infrared rays act differently?

  As the model shows, when sunlight (shown as yellow arrows) hits the Earth, much of it is absorbed into Earth systems (shown as dots uner the Earth's surface). Some of this energy is radiated back upward to the atmosphere in the form of longer-wavelength infrared radiation (shown as red arrows in the model).   Teachers: What's happening at the molecular level is that when energy is absorbed by matter (such as carbon dioxide gas) the atoms and molecules that make up the material get "excited" and move around faster. The increased movement raises the material's temperature.                                                                                                                                                                                                                                                                       Most of the infrared "rays" radiate back into space, but greenhouse gases are capable of absorbing and "trapping" the infrared energy. This is not a bad thing -- without the warming effects of greenhouse gases, our Earth would be almost as cold as Mars and possibly uninhabitable by humans. So why are we concerned? In the past 150 years, the concentration of greenhouse gases in our atmosphere has increased dramatically, resulting in measurable temperature increases. If left unchecked, the rising greenhouse gas concentration will have catastrophic effects on Earth systems and Earth's climate. 

Discussion: Wrapping Up

Activity 1

• What happens when radiation gets trapped in our Earth's atmosphere?

  When greenhouse gases absorb infrared radiation, they "trap" it in our atmosphere so it can't escape to space. If the greenhouse gas concentration gets too high, it traps enough infrared to produce a measurable rise in Earth's temperature. Human activities have altered the concentration of greenhouse gases in recent years, primarily due to burning of fossil fuels and deforestation.
  

• What is the relationship between temperature and carbon dioxide?
  
  There is a strong and direct correspondence between CO2 levels in the atmosphere and temperatures on Earth's surface. When carbon dioxide concentrations go up, temperatures go up. The reverse is also true. Throughout Earth's planetary history, levels of atmospheric CO2 have fluctuated. But scientists are concerned because the rate of increase in CO2 concentration has been unprecedented since the dawn of the Industrial Revolution. 

Additional Background

The Earth is getting warmer because people are adding heat-trapping gases to the atmosphere, mainly by burning fossil fuels. These gases are called greenhouse gases. Warmer temperatures are causing other changes around the world, such as melting glaciers and stronger storm events. These changes are happening because the Earth's air, water, and land are all linked within a larger planetary feedback system. The Earth's climate has changed before, but this time is different. People are causing these changes, which are happening faster than any climate changes that modern society has ever seen before. 

What evidence do we have that global climate is warming at an unprecedented rate? The following global effects have been measured and documented. You can view them at climate.nasa.gov

• Global sea level has risen 17 cm in the last century.
• Global surface temperatures have risen since 1880, with the 20 warmest years having occurred since 1981.
• Polar ice sheets have decreased in mass. Greenland lost 150-250 cubic kilometers of ice per year from 2002-2006, while Antarctica lost about 152 kilometers per year during the same time. 
• Arctic sea ice has declined rapidly over the past several decades.
• Glaciers are retreating everywhere around the world.
• Record high temperature events have been increasing, while record low temperature events have been decreasing since 1950. 
• Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30%.
• Satellite observations reveal that the amount of spring snow cover in the Northern hemisphere has decreased over the past five decades and that snow is melting earlier.

Analysis

Activity 1

• Are sun rays and infrared rays affected differently by albedo and cloud cover? Run the models again if that will help you answer this question. Draw below a diagram of the effect of albedo (reflective power of a surface) and cloud cover.

  Student answers will vary depending on what parameters are used in the simulation. In general, expect students to realize that higher albedo will result in more reflection of solar radiation, producing lower surface temperatures, while low albedo will result in higher surface temperatures. Regarding cloud cover, students should discover that heavy cloud cover prevents penetration of some solar radiation, while low cloud cover allows much fuller penetration of solar rays to Earth's surface. 

• What physical changes to Earth could change its albedo?

  Some acceptable responses include: melting of polar ice, retreat of glaciers, increase in area used for farming, decrease in snow cover, decrease in ice cover on the oceans. 

• Different local areas often report large year-to-year changes in their climate, in terms of temperature and precipitation. Yet the average temperature of the Earth (the whole planet) is quite steady. A one degree Celsius change in the average temperature of the whole planet would be very large! Explain how this could be the case.

  This is a simple question with a complex answer, so responses will vary. Students may need guidance to understand that small changes in average global temperature can have profound effects. It will help to point out that there's a huge difference between mean temperature of Earth's entire surface area and temperature fluctuations in one locale. Here are some example statistics from the National Research Council report: Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia (2011):

• 200-400% increase per degree in area burned by wildfires in western United States
• 5-10% less rainfall per degree  in the Mediterranean, SW North America, and southern Africa dry seasons
• 5-10% more rainfall per degree in Alaska and other high-altitude Northern Hemisphere areas
• 5–15% reduced yield of US corn, African corn, and Indian wheat per degree
• 15% and 25% reductions in Arctic sea ice area per degree

Activity 2

• Using the draw tool, make your own diagram of what happens to light rays and infrared rays when there are clouds and greenhouse gases present in the atmosphere

  Student diagrams will vary but they should include pictures of the source of light and infrared rays and the position of them when clouds and greenhouse gases are present

• Make a list of the important greenhouse gases. For each one, write down sources of this gas, and whether the source is natural or man-made.

• Methane emissions:  Natural gas and petroleum production: 30% (man-made), Digestive fermentation by grazing animals: 25% (natural), Landfills: 18% (man-made), Coal Mining: 10% (man-made), Other: 17%

• Carbon dioxide: Let's divide this into two categories. #1: Natural Sources of CO2:  Ocean/Atmosphere Exchange-42%, Plant and Animal Respiration-29%, Soil Respiration and Decomposition-28%. #2: CO2 emissions caused by burning of fossil fuels. Here is a breakdown of how these fossil fuels are utilized -- Energy production: 26%, Automobiles: 13%, Industry: 20%, Agriculture: 14%, Forestry: 17%, Other: 10%

• Nitrous Oxide Most comes from agricultural activity (primarily from synthetic fertilization, which is man-made)); some comes from biomass burning and human and livestock sewage

• As you may have noticed as you watched the model, incoming rays of sunlight are not affected by the greenhouse gas molecules. On the other hand, infrared radiation is strongly absorbed by greenhouse gas molecules. Explain why this could cause Earth's temperature to rise.

  Infrared is a type of electromagnetic radiation which has longer wavelengths than those of visible light. The heat we feel from the sun, a fireplace, or a radiator is infrared radiation. When infrared is trapped by a molecule, that molecule absorbs the thermal radiation. In the case of the Easth's atmosphere, this heat is reflected back to the Earth's surface, making it warmer.

• The model also shows the effect of cloud cover. Do clouds have the same effect as greenhouse gases? Explain.

  When water vapor condenses to form clouds, the latent heat is "released," like a genie from a bottle. The newly liberated latent heat warms the air. You may have experienced warming by latent heat release in a sauna. When water is thrown on the hot coals, vapor is produced. The vapor then condenses on your skin, releasing its latent heat and making your skin feel hot. Similarly, when water vapor condenses to form clouds, the released latent heat makes the air warmer. A second, more obvious effect of clouds on the energy of the climate system is that they reflect sunshine back to space, cooling the Earth. This is particularly true for low stratus clouds.Conversely, cold high clouds, especially cirrus clouds, reduce the infrared radiating out to space. This tends to warm the Earth, and is part of the greenhouse effect.Clouds drop rain and snow on the surface. Strong updrafts in thunderstorms carry energy and moisture (and other things) from near the surface to the upper troposphere and sometimes the lower stratosphere.

Further Investigation

Students may wish to run the simulation again to address the following questions.

Activity 1

• What happens when sunlight strikes Earth?

  ...

Activity 2

• How does Earth's atmosphere affect the radiation energy balance?

  ...