NSTA Climate Physics

8/2/2019 NSTA Climate Physics

1/4

T Sin T44

Numerous connections exist between climatescience and topics normally covered in physicsand physical science courses. For instance, les-sons on heat and light can be used to introduce

basic climate science, and the study o electric circuitsprovides a context or studying the relationship betweenelectricity consumption and carbon pollution. To highlightsome o these connections, this article describes a serieso lessons and activities that use basic physics concepts toteach about climate change. The examples may help teach-ers notice and emphasize additional correlations betweentheir own existing physics programs and climate science.

In my high school physics classes, climate change pro-vides a uniying theme or the second semester. The cur-riculum outline in Figure 1 shows the ull range o topicsI have been able to connect to climate science in recentyears. I spread these lessons across the entire semester, butthey could also be taught consecutively as a separate unitin a physics or environmental science class.

This article rst explains how I introduce and integratebasic climate topics into units on heat and electromagneticradiation. The second part o this article explains how aunit on electric circuits provides a useul context or dis-cussing ways to solve the problem o climate change. Ex-

planations o specic activities are kept brie to allow or arelatively comprehensive survey o the possibilities.

Heat and electromagnetic radiation

The second law o thermodynamics tells us that energy nat-urally fows rom hot things to cold things, and the Stean-Boltzmann law states that hotter objects radiate moreenergy than cold ones. These two laws orm the basis ora very simple model o the interaction between the Sun,Earth, and empty space (Figure 2). I generally completethe ollowing sequence as a class demonstration to acili-tate discussion. However, the experiments described could

Using basic physics concepts to teach about climate change

easily be conducted by small groups i saety concernsposed by hot objects are adequately addressed.

To begin, place a beaker ull o water on a hot plate andset the plate to low or medium. The water will warm atrst but eventually will reach an equilibrium temperature.This happens because as the temperature o the waterincreases, the corresponding rate at which the water losesenergy to the cooler surrounding air also increases. Even-tually the increasing rate at which the water loses energyto its environment equals the rate at which the water ab-sorbs energy rom the hot plate, and the system reachesequilibrium. At this point, I explain that Earth and the

Sun are in a similar state o equilibrium, in which theamount o energy Earth receives rom the Sun is equal tothe amount radiated back into space. Careul applicationo the Stean-Boltzmann law, however, predicts a muchlower temperature on Earth than is actually observed, sothe model is incomplete.

Now place a loose lid on top o the beaker. The rate atwhich heat leaves the beaker will decrease and the tem-perature will begin to increase. This temperature increasewill cause the rate o heat loss to once again increase until anew, higher-temperature equilibrium is reached. I explainto my students that carbon dioxide plays the role o the lid

in Earths atmosphere, and the carbon dioxide that existsnaturally in the atmosphere keeps Earths surace warmenough to support the various lie orms that studentsstudy in their biology classes. Adding another lid to betterinsulate the top o the beaker simulates the consequenceso adding carbon dioxide to the atmosphere by burningossil uelsa new higher equilibrium temperature willbe reached.

O course, this model is ar rom complete. Earths at-mosphere, surace, and oceans orm a complex, interactingsystem. Some o these complexities are relevant, such asthe act that warming will melt refective white ice caps or

By Wil l iam Space


2/4

Stb 2007 45

may lead to the ormation o more refective white clouds.Because some o the more poorly understood o these pro-cesses have the potential to partially counteract the warm-ing eects o additional carbon dioxide, the processeshave been much discussed by people who argue againststrong government responses to climate change (Figure

3). Students should be encouraged to discuss these physicalprocesses and political controversies, but teachers shouldalso stress the degree to which most climate scientistsexpect the underlying eect, captured in the model justdescribed, to predominate.

A more serious problem with the hot plate model isthat it does not show how Earths carbon dioxide lidkeeps heat in without keeping sunlight out. In the same

way walls are transparent to radiowaves but opaque to visible light,carbon dioxide is transparent tovisible sunlight but opaque to theinrared light emitted rom themuch cooler Earth. Inrared ra-

diation causes the chemical bondsin carbon dioxide to vibrate and thus absorb the inraredradiation, trapping it in the atmosphere.

To show that radiation rom hot and cold objects di-ers in wavelength, use a Bunsen burner to heat an ironrod until it is orange or even white hot. Then watch thecolor change as it cools and explain that the iron rod stopsglowing not because it stops emitting electromagneticradiation, but because our eyes are insensitive to the in-rared radiation emitted by cooler objects. I have oundthe computer simulations Blackbody Spectrum and TheGreenhouse Eectavailable or ree download rom the

Physics Education Technology project at the University oColoradoto be invaluable in teaching about this concept(Figure 4, p. 46).

In general, these problems with the hot plate model can

F i g u r e 1

Sample climate physics curriculumoutline.

Thermal Physics (February, about two weeks)

u thermodynamics and heat ow

u thermal expansion o seawater

u heat engines and efciency

Electromagnetism (March and April, about six weeks)

u electric circuits and consumption in homes

u resistive heating and transmission losses

u electric motors and generators

Waves and Light (April and May, about six weeks)

u absorption spectra and the greenhouse eectu blackbody radiation and temperature

u the photoelectric eect and photovoltaic cells

Nuclear Physics (May and June, about two weeks)

u nuclear fssion and nuclear power plants

u nuclear usion as a potential energy source

F i g u r e 2

Climate physics summarized.

The Sun radiates energy, partly in the orm o visible light,

because it is hot. The Earth also radiates energy, but because

it is not as hot as the Sun, most o Earths radiation takes the

orm o an invisible orm o radiation called infrared. Visible

light rom the Sun passes through the atmosphere and warms

Earths surace, but inrared light radiated rom Earth is absorbed

by carbon dioxide molecules in the atmosphere. The carbon

dioxide in the atmosphere thus orms a blanket that keeps our

planet warm enough or us to survive. Adding carbon dioxide

to Earths atmosphere, which we do when we burn ossil uels,

is somewhat like throwing an additional blanket on top o a

contented sleeper.

F i g u r e 3

Climate skeptics.

There is no scientifc debate about the role that carbon

dioxide plays in keeping us warm, or about the act that

the concentration o carbon dioxide in the atmosphere is

increasing signifcantly as we burn ossil uels. Also, there is a

broad and growing consensus that some warming has alreadybeen observed. However, skeptics o global warming argue that

the media consistently exaggerates the need or preventative

action. These people make the ollowing three points:

u Current understanding o Earths climate is not complete

enough to support specifc quantitative predictions o

uture warming. For example, the role o clouds is not well

understood.

u Climate changes, i they occur, will have some positive

eects, such as lengthened growing seasons.

u It would be very difcult and expensive to signifcantly limit

carbon emissions.One powerul skeptic is Senator James Inhoe o Oklahoma. His

statements on the subject can be downloaded rom the U.S.

Senate website and used to stimulate classroom discussion.

Inhoe is the ranking member o the Senate Environment and

Public Works Committee; an interesting debate can be started

by comparing Inhoes views with those o the chairman o the

committee, Barbara Boxer. A good place to start would be the

March 21, 2007 hearing o the committee that eatured ormer

Vice President Al Gore (http://epw.senate.gov/public/index.

cfm). Will science ever resolve this controversy?

Keywords: Climate change

at www.scilinks.org

Enter code: TST090702


3/4

T Sin T46

be approached in two very dierent ways. I have gener-ally chosen to stress the act that all models are incomplete.While the hot plate/lid/beaker system is dierent rom thecorresponding Sun/atmosphere/Earth system in many un-damental ways, it has enough similarities to be useul andstudents can benet rom a discussion o its strengths and

weaknesses. Another approach would be to challenge stu-dents to improve the model, or example, by using a heatlamp instead o the hot plate and using a glass lid.

Electric circuits

Some students are aware that carbon dioxide is createdand released into the atmosphere when gasoline is burned.But ew students may realize that when they turn ona light switch, a power plant somewhere burns a littlemore coal or natural gas and emits a correspondingamount o carbon dioxide. While the United States does

generate some o its electricity rom nonossil sources,including nuclear reactors, production rom these powerplants is constrained by actors other than short-termvariations in demand (Figure 5). A unit on electric circuitsprovides a useul context or introducing the idea that,by changing the way electricity is generated, transmitted,

and consumed, carbon dioxide emissions can be decreased(Figure 6).

For students, the generation o electricity is the mostinteresting and least understood part o the sequence, soI discuss the operation o a traditional, ossil uelredpower plant at the beginning o the semester. These powerplants convert chemical potential energy into heat and thenelectrical energy, so this provides a good opportunity toexplain the relevant chemistry and review the law o con-servation o energy. At this point each student in my classchooses an alternative, carbon-ree energy source that they

F i g u r e 4

Blackbody spectrum.

How does the blackbody spectrum of the Sun actually compare to that of Earth? Students can compare the spectra using

a simulation available at http://phet-web.colorado.edu/web-pages/simulations-base.html. Students adjust the temperature

(using the interactive slider pictured) to see that the Earth and Sun spectral curves peak at very dierent wavelengths, and teachers

explain that carbon dioxide absorbs the longer wavelength radiation emitted by the cooler Earth. This greenhouse eect is more

explicitly modeled in another simulation available rom the same source.

Image prINTed wITh permISSIoN of The pheT projecT, UNIverSITy of colorado (http://phet.colorado.edu).


4/4

Stb 2007 47

will research throughout the semester and present to theclass at the end o the year.

My students also study two things to amiliarize them-selves with electricity consumption in their homes. First,students write down inormation about voltage, current,resistance, and power that is printed on electrical devices

in their homes and use the inormation to estimate month-ly electric consumption or dierent devices. Second, stu-dents examine their amilies electric bills to determine thecost o each kilowatt-hour o electricity. These activitiesare included here not because they are new or creative, butrather to suggest that teachers should use the additionalopportunities to point out the relationship between electri-cal consumption and carbon emissions.

Getting started with climate physics

There was no single point in time when I decided toorganize the second semester o my physics classes around

the theme o climate change. Instead, the more I learnedabout the topic, the more I noticed connections with myphysics curriculum. Hopeully teachers who read this

article will also realize these connections and, ideally, indadditional connections not identiied here.

Biology teachers have, in recent decades, been able touse a constant stream o new discoveries and very relevantnews stories to instill appreciation or science as an ongo-ing, relevant, and oten controversial process (e.g., thepublic discussion about evolution).

In contrast, the standard physics curriculum includesrelatively ew such opportunities. By teaching about cli-mate change, physics teachers can help students to see

physics as useul, relevant, and interesting. Teachers willnd that students begin to ask questions about discussionsheard at home, things seen on television, and stories readin newspapers. These student-centered discussions areimportant because they excite the interest o students in away that no amount o isolated direct instruction can.

Interwoven instruction about climate change makeslessons about heat, light, electricity, and nuclear physicsmore relevant and interesting or both students and teach-ers. Perhaps more importantly, knowledge o basic physicscan help students to better understand and eventually in-fuence political debates about climate change. n

Wiim S (ss@.) is ysis N

Smifi Jni-Sni hig S in N Smifi,

r Isn.

Resources

Boeker, E., and R. Grondelle. 2001. Environmental science: Physical

principles and applications. United Kingdom: Wiley.

Houghton, J. 2004. Global warming: The complete briefng. United

Kingdom: Cambridge University Press.

Sweet, W. 2006.Kicking the carbon habit: Global warming and the case or

renewable and nuclear energy. New York: Columbia University Press.

F i g u r e 5

Nuclear power.

Growing concern about climate change may revive the

debate about nuclear power. Nuclear plants are currently the

largest source o carbon-ree electricity in the United States,and some people have begun to argue or new reactors to

combat climate change. However, others, including many

o the environmentalists who worry most about climate

change, oppose the construction o new reactors because o

concerns about reactor saety, nuclear waste, and weapons

prolieration.

Ater a lesson about nuclear fssion, students can debate

or discuss the ollowing hypothetical scenario: A company

proposes the construction o a new nuclear power plant

in your state, asserting that the new plant is necessary i

eorts to limit carbon emissions are to succeed. Would you

support such a proposal? (Note: Both sides o this debateproduce propaganda that can be misleading. For this to be a

learning experience, the teacher must have some amiliarity with

the various arguments and be prepared to show impartiality

or both sides.)

F i g u r e 6

Motors, circuits, and energy efciency.

Efciency is a measure o how little energy is required to

accomplish a specifc task. Students can conduct the ollowing

activity to develop a mathematical understanding o efciency.

Connect a small electric motor to a power source, ammeter,and voltmeter. Clamp the motor to a stand and wrap a string

around the shat. Use the motor to lit a small weight.

u Calculate the amount o gravitational potential energy

gained by the weight. (Eg

= mgh; m = mass,g = 9.8 m/s2, and

h = height.)

u Calculate the amount o electrical energy provided by the

motor. (Ee

= VIt; V= voltage, I = current, and t= time.)

u To calculate the efciency, divide the gravitational energy by

the electrical energy and write the answer as a percentage.

The answer should be much less than one.

u Repeat the experiment with dierent weights and dierentspeeds. Do these changes aect the efciency o the motor?

How? Why?

The discussion o efciency can be extended by asking students

to research how cars can be made to use gasoline more

efciently. An entire class should be able to compile a very

long list. Students can also calculate savings that result rom

replacing incandescent lightbulbs with much more efcient

compact uorescent bulbs. In each case, using less energy

cuts carbon emissions.

Documents

NSTA Climate Physics