Key unit Competence 

    By the end of the unit, I should be able to evaluate climate change and greenhouse effect. 

    My goals 

    • Explain concepts of climate change  

    • Explain causes of climate change

    • State the Stefan-Boltzmann law and apply it to emission rates from different surfaces  

    • Outline the nature of black body radiation and its emissivity  

    • Evaluate concept of emissivity and relate to emission rates for different surfaces.  

    • Carry out an investigation on greenhouse effect  

    • Make observations and ask questions on climate change, Identify problems and formulate hypotheses to investigate climate change in surrounding environment 

    Introductory activity 

    Most of the solar radiation that is incident onto the Earth is absorbed and the rest is reflected back into the atmosphere. Our Earth acts almost as a black body, thereby it radiates back to the space part of the energy it has absorbed from the sun. The earth and its atmosphere is a part of the solar system. Life on the Earth cannot exist without the energy from the sun. a. Basing on Physics concepts, how do humans and plants get energy from the sun? Give the major source of this energy?

    a. Do humans and plants maintain the energy absorbed forever? Explain your reasoning using physics concepts. 

    b. State and explain the scientific term used to describe a body that can absorb or emit radiations that fall on them. 

    c. Basing on your ideas in (c) above what could be the effect on that body if: 

    I. It maintains the energy for a long time

    II. Reflects energy after a given time. 

    III. Do you think that these reflected and absorbed radiations have effect on the Climate? Why? Discuss your answers with your friends and even present it to your Physics teacher


    2.1.1 Black body radiation 

    Activity 2.1: black body radiation 

    • Try to get two clothes of the same kind (similar material) but of different colour black and White   

    • Soak them in water at the same time 

    • Display them to places of the same sunlight intensity. 

    • Check them after like 20 min, 30 min, or 40 min. 

    • Observe how they are drying up.

    • Make a comprehensive report about your findings.  

    • Relate your findings to the concept of black body and hence define ‘a black body’ 

    • From your deductions, explain what happens when the temperature of a black body increase 

    • You can share your observations and findings with your friends and even to your teacher. 

    An object that absorbs all radiation falling on it and therefore emitting radiation in whole spectrum of wavelengths is called a blackbody. At equilibrium temperature a black body has a characteristic frequency spectrum that depends only on its temperature. 

    A perfect blackbody is one that absorbs all incoming light and does not reflect any. At room temperature, such an object would appear to be perfectly black (hence the term blackbody). However, if heated to a high temperature, a blackbody will begin to glow with thermal radiation. 

    2.1.2 Laws of black body radiation 

    a. Stefan-Boltzmann law The law states that, “the power per unit area radiated by a surface of a black body is directly proportional to the forth power of its temperature”.


    Using this formula, we can calculate the amount of power radiated by an object. A black body which emit in whole spectrum of wavelength would have an emissivity of 1. Since the earth is not a perfect black body, it has a certain emissivity value. The emissivity is defined as the power radiated by a surface divided by the power radiated from a perfect black body of the same surface area and temperature

    In simpler terms, it is the relative ability of a surface to emit energy by radiation. A true blackbody would have an emissivity of 1 while highly polished silver could have an emissivity of around 0.02. The emissivity is a dimensionless quantity.

    b. Wien’s displacement law

    It states that“the maximum wavelength of the emitted energy from a blackbody is inversely proportional to its absolute temperature”. This law was formulated by the German physicist Wilhelm Wien in 1893 who related the temperature of a black body and its wavelength of maximum emission following the equation


    Quick check 2. 1: When an iron bar is heated at high temperatures it becomes orange-red and its color progressively shifts toward blue and white as it is heated further. Explain this observation? 


    It is not good to put on black clothes on a sunny day. This is because these dark clothes will absorb more radiations from the sun which may be harmful to our health.

    2.1.3 Black body radiation curves


                            Fig.2. 1 Black body radiation curves showing peak wavelengths at various temperatures 

    This Fig.2.1 shows how the black body radiation curves change at various temperatures. 

    The graph indicates that as the temperature increases, the peak wavelength emitted by the black body decreases. It therefore begins to move from the infra-red towards the visible part of the spectrum. Again, none of the graphs touch the x-axis so they emit at every wavelength. This means that some visible radiation is emitted even at these lower temperatures and at any temperature above absolute zero, a black body will emit some visible light. Features/Characteristics of the Graph  

    • As temperature increases, the total energy emitted increases, because the total area under the curve increases.

    • It also shows that the relationship is not linear as the area does not increase in even steps. The rate of increase of area and therefore energy increases as temperature increases. 

    2.1.4 Checking my progress

    For the questions listed below, re-write the questions in your notebooks and CIRCLE the best alternative 

    1. What is the black body or an ideal radiator?

    a. The body which transmits all the radiations incident upon it 

    b. The body which absorbs all the radiations incident upon it  

    c. The body which reflects all the radiations incident upon it 

    d. None of the above 

    2. As a radiator, the black body emits the maximum possible thermal radiation  

    a. At the constant single wavelength    

    b. At all Possible wavelengths  

    c. At a maximum wavelength    

    d. None of the above 

    3. Which of the following sentences are correct for black body 

    I. The black body is a hypothetical body

    II. The black body is a real body

    III. The black body is used as a standard of perfection against which the radiation characteristics of other bodies are compared 

    A. sentences (i) and (ii)

    B. sentences (i) and (iii)    

    C. sentences (ii) and (iii)   

    D. all the sentences (i), (ii) and (iii)


    2.2.1 Intensity of the sun’s radiation and albedo 

    Activity 2.2: Intensity of the sun’s radiation 

    Below is a stove of a gas cooker producing heat (You can use a Bunsen burner in your laboratory)

                                                                 Fig.2. 2 Stove of a gas cooker


    a. Light up the stove or Bunsen burner provided 

    b. Come close to the lighting Bunsen or stove. In your words write down what you are experiencing in terms of heat. 

    c. Place conductor (You can use an old iron sheet) between you and the source. Can you still receive the same amount of heat from the source? Explain why? 

    d. Relating the scenario above with the transfer of heat (radiation) from the sun, how does sun’s heat (radiations) reaches us, and other planets, 

    e. If you are far away from the source, can you receive the same amount as someone near it? Relate it to the transfer of heat from the sun to different planets explain your reasoning. 

    f. In your own words, explain the factors that determine a body’s ability to absorb or reflect a certain radiation

    Sun produces heat of very high intensity that is spread and then received by all surrounding objects. These objects include all the planets and other objects around it.
    The intensity of the sun (at the top of the earth’s atmosphere) is approximately 1400 W/m2 also known as the solar constant. The amount received on the earth surface is slightly below 1400 w/m2.The main reasons for variation in intensity include: 

    The shape of the earth: The earth has a spherical shape and therefore the sunlight is more spread out near the poles because it is hitting the earth at an angle, as opposed to hitting the earth straight-on at the equator. There are also fewer atmospheres at the equator, allowing more sunlight to reach the earth. Therefore, the intensity varies depending on the geographical latitude of the earth’s location.

    The earth’s rotation: all areas are not consistently exposed to sunlight. Areas that are experiencing ‘nighttime’ are not receiving a lot of the sun’s power; therefore the time of the day or night will affect the solar constant. 

    The angle of the surface to the horizontal at that particular location: When the Sun is directly overhead, its rays strike Earth perpendicular to the ground and so deliver the maximum amount of energy. When the Sun is lower in the sky, a sunbeam strikes the ground at an angle and so its energy is “spread out” over a larger area 

    The solar constant represents the mean amount of incoming solar electromagnetic radiation per unit area on the earth’s surface. This constant takes into account all types of solar radiation, including UV and infrared. The accuracy of the solar constant is questionable due to the following generalizations: This radiation is assumed to be incident on a plane perpendicular to the earth’s surface. It is assumed that the earth is at its mean distance from the sun. 

    Our seasons also determine how much Sun’s radiation strikes a square meter of ground in a given place on the planet’s surface at a given time of the year. The sun’s radiation is maximum in the summer and it is minimum in winter

    Scientists use a quantity called “albedo” to describe the degree to which a surface reflects light that strikes it. It can be calculated by the ratio of reflected radiation from the surface to the incident radiation upon it.

    The albedo has no units since it is a ratio of the similar quantities. Being a dimensionless fraction, it can also be expressed as a percentage and is measured on a scale from 0 (0%) for no reflective power to 1 (100%) for perfect reflectors. The earth’s albedo is about 0.3, meaning, on average, 30% of the radiation incident on the earth is directly reflected or scattered back into space. An object that has no reflective power and completely absorbs radiation is also known as a black body.


                                        Fig.2. 3: The transmission of light (heat) from the sun to the Earth
    The table below gives you some values of estimated albedo for various surfaces expressed as percentages: 


                                                                            Table 2. 1 Albedo for various surfaces 

    Some other facts about sun 

    1. At its centre, the sun reaches temperature of 15 million degrees Celsius 

    2. The sun is all the colors mixed together, this makes it appear white to our eyes. 

    3. The sun is mostly composed of hydrogen (70%) and Helium (28%) 

    4. The sun belongs to the main Sequence G2V star (Yellow Dwarf) 

    5. The sun is about 4.6 billion years old 

    6. The sun is about 100 times wider than the earth and 3330 000 times as massive 

    Activity 2.3: 1

    a. With clear explanations, explain the approximate spectral composition of the Sun’s radiation before it interacts with Earth’s atmosphere? 

    b. Is the amount of solar energy that reaches the top of Earth’s atmosphere constant? Explain giving valid examples and evidence. 

    c. Are all wavelengths of Sun’s radiation transmitted equally through Earth’s atmosphere? Explain your reasoning. 

    2. a. What effect does absorption have on the amount of solar radiation that reaches Earth’s surface?

        b. List down other processes (besides absorption) that affect radiation reaching the earth’s surface? 

    c. What can be percentage of incoming solar radiation that is affected by absorption and scattering (or reflection)? 

    3. a. Jane Says that clouds have a high albedo while Pierre says land vegetation has a low albedo? Using Scientific explanations, Discuss what they base on to make their deductions 

    b. What do you think are major factors that influence the insolation at a particular location on a particular day? How do they affect it? 

    c. What latitudinal regions experience least variation in day-to-day solar radiation? Which one experiences the greatest? Why?


    The text below is incomplete as it misses some of the technical terms. Using the knowledge and idea about albedo, re-write the text in your notebook and fil the spaces with the words given in the brackets (Aerosols, Deforestation, Lifetime, Climate, Infrared Radiation)to complete the text. 

    a. There are many factors that affct the Earth’s _________. Snow and ice are highly reflctive so when they melt, _____________ drops.  b. Forests have a lower  ________  than open land so ___________ increases ___________ 

    c. __________ have a direct and indirect effct on _______________.

    d. The direct effct is by reflcting sunlight back into space, cooling the Earth. 

    e. The indirect effct is when aerosolparticles act as a cloud condensation nucleus, affcting the formation and ______________of clouds.

    f. Clouds in turn inflence global temperatures in various ways. 

    g. They cool the ________ by reflcting incoming sunlight but can also warm the ___________ by trapping outgoing _____________from the surface

    2.2.2 Factors affecting Earth’s albedo

    mong other factors, the following are some of the factors that affect the albedo of the earth: 

    • Clouds: The atmosphere is usually covered with clouds that usually pass over the earth’s surface. This leads to reduction or increase in the temperature of the earth’s surface. This is because these clouds may absorb or reflects back sun’s light to the free space. However, this depends on the distance from which the clouds are from earth’s surface. When sun’s radiation is reflected, the earth’s surface is cooled and when it is absorbed the earth is warmed. 

    • Oceans: While observing from the space, you will find out that water bodies appear differently from land surfaces. They appear darker and therefore absorb more sun’s radiations than land. However, some of the radiations heating the water surface (ocean) may be carried away by the currents while others may form water vapor. 

    • Thick vegetation covers or forested areas: Places covered with vegetation absorb a lot of sun’s radiation. This is because the vegetation cover provides a dark surface which absorbs more radiations than the bare land.  

    • Surface albedo: Different surfaces appear differently. Light coloured surfaces absorb different amounts of radiations than dark coloured surfaces. Snow covered areas are highly reflective. They thus absorb less amounts of energy (Sun’s radiation). The snow cover reduces the heating effect of the earth’s surface. 

    However, if temperatures reduce, the snow cover reduces leading to the absorption of radiation by the exposed ground surface.

    2.2.3 Checking my progress

    For questions 1-4 below, re-write them in your notebook and CIRCLE the best alternative of your choice 

    1. Which of the following has high Albedo? 

          a. Asphalt parking lot 

          b. Snow-covered field

          c. They have the same albedo

          d. Some information is missing for this question 

    2. Imagine you are having two places: a desert and a forest. Which one has lower albedo,? 

         a. Desert

         b. Forest

         c. They have the same albedo 

         d. This question lacks some information 

    3. Imagine you are looking at two Areas of land while flying over in a jet at midday. Plot #A looks very bright. Plot #B looks very dark. Which area of land has a lower albedo? 

         e. Plot #A 

         a. Plot #B 

         b. They have the same values for albedo 

         c. More information is needed to answer this question 

    4. Refer to the list of albedo values (below). Order these three surfaces - fresh snow, grasslands, and asphalt - from highest albedo to lowest albedo. 



                                                        Fig.2. 4: Greenhouse effect

    Discovery Activity 2.5 

    a. What do you know about greenhouse?

    b. Different activities like industrialization and others give out gases after burning fossil fuels. I. What special name is given to these gases? II. If these gases accumulate in the atmosphere, what effect do they have on to the temperature of the earth and its atmosphere? 

    c. Suggest measures that can be done to limit high accumulation of these gases in the atmosphere. 

    d. Discuss your findings with your classmates and even to your teacher. Come up with a general stand from your findings

    The relationships between the atmospheric concentration of greenhouse gases and their radiative effects are well quantified. The greenhouse effect has the root from greenhouses that becomes warmer when heated by sun’s radiation. The mode of operation of a green house is that a part of the sunlight radiations incident on the ground surface of the greenhouse are absorbed and warms the surface inside the greenhouse. Both the reflected radiations and the heat emitted by the ground surface in the greenhouse are trapped and re-absorbed inside the structure. Thus, the temperature rises inside the greenhouse compared to its surrounding environment.

    Therefore, the greenhouse effect heats up the earth’s surface because the green gases that are in the atmosphere prevent radiations from leaving the atmosphere. The absorption of these radiations contributes to the increase of the atmosphere’s temperature.

    Note: green gases act as a glass or plastic in greenhouses 

    A greenhouse is constructed by using any material that allows sunlight to pass through usually plastic or glass. This prevents reflected radiations from leaving the structure thereby leading to the increase in the temperature within. If a small puncture is made on to the greenhouse, the temperature within reduces. 

    PROJECT: 2.1 

    Construct a greenhouse (Can be done in a period of 3 months) In this project you may need 

    • Polyethene paper or plastic or glass. 

    • Wood 

    • Nails 

    • Any fiber that can be used while Tying 


    a. Using materials listed above, construct a small greenhouse. It Can be done at School or at home. 

    b. Sow any seed inside. 

    c. After seeds have germinated, see the changes in the development of the plant. 

    d. Make a comprehensive Report about your Greenhouse. Include temperature and vapor changes within the green house. 

    e. Share it with your friends or your teacher.

    By definition therefore, Greenhouse effect is the process by which thermal radiation from the sun is prevented from leaving the atmosphere and then re-radiated in different directions. 

    Since some of these re-radiated radiations come back to the earth’s surface, they lead to the increase in the temperature of the earth’s surface leading to global warming.


                             Fig.2. 5: (a) Greenhouses in one of the parts of Rwanda and (b) emission of greenhouse gases.

    2.3.1 Greenhouse gases 

    Some gases in the earth’s atmosphere act a bit like the glass in a greenhouse, trapping the sun’s heat and stopping it from leaking back into space. Many of these gases occur naturally, but human activity is increasing the concentrations of some of them in the atmosphere, in particular: 

    a. Carbon dioxide (CO2) 

    b. Methane 

    c. Nitrous oxide 

    d. Fluorinated gases 

    CO2 is the greenhouse gas most commonly produced by human activities and it is mainly responsible for man-made global warming. Its concentration in the atmosphere keeps on increasing with industrialization. Other greenhouse gases are emitted in smaller quantities, but they trap heat far more effectively than CO2, and in some cases are thousands of times stronger. Methane is responsible for 17% of man-made global warming, nitrous oxide for 6%.

    Causes for rising emissions: 

    Burning coal, oil and gas that produce carbon dioxide and nitrous oxide. Cutting down forests (deforestation). Trees help to regulate the climate by absorbing CO2 from the atmosphere. So when they are cut down, that beneficial effect is lost and the carbon stored in the trees is released into the atmosphere, adding to the greenhouse effect. 

    Increasing livestock farming. Cows and sheep produce large amounts of methane when they digest their food.

    Fertilizers containing nitrogen produce nitrous oxide emissions. 

    Fluorinated gases produce a very strong warming effect, up to 23 000 times greater than CO2. Thankfully these are released in smaller quantities and are being phased down by European Union regulation.

    Activity 2.6: 

    Emitted greenhouse gases worldwide from 1990 to 2005

    Below is a bar graph showing emitted Greenhouse gases worldwide from 1990 to 2005. Use it to answer the questions that follow.


    Fig.2. 6 Emissions of greenhouse gases worldwide from 1990 to 2005 by Rwanda Environment Management authority (REMA) 

    a. From your analysis (using the graph) which kind of gas was emitted in excess for the specified period? What could be the factors that led that gas to be emitted in large quantities? 

    b. What do you think one can do to limit such emissions? 

    c. From your own point of view, do you think it’s a good idea to stop completely emission of these gases? Explain your reasoning by giving valid examples.

    Solutions to reduce the impact of greenhouse gases

     • High efficiency during power production 

    • Replacing coal and oil with natural gas 

    • Combined heating and power systems (CHP) 

    • Renewable energy sources and nuclear power 

    • Carbon dioxide capture and storage 

    • Use of hybrid vehicles.

    2.3.2 Impact of greenhouse effect on climate change. 

    With the greenhouse effect, the earth is unable to emit the excess heat to space and this leads to increase in atmosphere’s temperature and global warming. Scientists have recorded about 0.75°C increase in the planet’s overall temperature during the course of the last 100 years. The increased greenhouse effect leads to other effects on our climate and has already caused: (REMA) 

    • Greater strength of extreme weather events like: heat waves, tropical cyclones, floods, and other major storms. 

    • Increasing number and size of forest fires. 

    • Rising sea levels (predicted to be as high as about 5.8 cm at the end of the next century). 

    • Melting of glaciers and polar ice. 

    • Increasing acidity in the ocean, resulting in bleaching of coral reefs and damage to oceanic wildlife. 

    2.3.3 Global warming 

    Global warming is the persistent increase in temperature of the earth’s surface (both land and water) as well as its atmosphere. Scientists have found out that the average temperature in the world has risen by about 0.750C in the last 100 years and about 75% of this rise is from 1975. Previously the changes were due to natural factors but currently the changes are due to both natural and human activities. From research, natural greenhouse maintains the temperature of the earth making it a better place for human kind and animal life. However ever since the evolution of industries, there has been significant change in the temperature. The causes are both natural and human activities: 

    a. Human activities 

    Burning of fossil fuels: These emit carbon dioxide gases when heated that accumulate in the atmosphere. These gases absorb and may not allow sun’s radiation to pass through. This in turn leads to an increase in the temperature of the earth’s atmosphere, hence global warming. These fuels are burnt in vehicles and in industries. 

    • Deforestation. Plants use carbon dioxide in manufacturing their food.  

    • This implies that trees reduce amount of carbon dioxide in the atmosphere. Cutting down these trees therefore leads to part of carbon dioxide remains unused. This is a big problem 

    • Agriculture: Agriculture is a good practice. Though if not handled with care, it may lead to destruction of nature which is a big problem

    • And all other infrastructure development: These include, urbanization, road construction and places for settlement. These have contributed to the destruction of nature.

    b. Natural causes 

    • Volcanicity: When volcanoes erupt, they throw out large volumes of sulphur dioxide (SO2), water vapor, dust, and ash into the atmosphere. Although the volcanic activity may last only a few days, the large volumes of gases and ash can influence climatic patterns for years. Millions of tones of sulphur dioxide gas can reach the upper levels of the atmosphere (called the stratosphere) from a major eruption. 

    • Ocean currents: Oceans plays a major role in the change of climate. Oceans cover about 71% of the Earth and absorb about twice as much of the sun’s radiation as the atmosphere or the land surface. Ocean currents move vast amounts of heat across the planet - roughly the same amount as the atmosphere does. But the oceans are surrounded by land masses, so heat transport through the water is through channels. 

    All the above practices lead to high concentration of greenhouse gases in the atmosphere especially carbon dioxide gases.

    Note: If these greenhouse gases were completely not there, the Earth would be too cold for humans, plants and other creatures to live.

    Can you now see the importance of these greenhouse gases! Though they cause greenhouse effect, they are responsible for regulating the temperature of the earth. 

    Global warming is damaging the earth’s climate as well as the physical environment. One of the most visible effects of global warming can be seen in the Arctic region where glaciers, permafrost and sea ice are melting rapidly. Global warming is harming the environment in several ways. 

    Global warming has led to: desertification, increased melting of snow and ice, sea level rise, stronger hurricanes and cyclones

    2.3.4 Checking my progress

    1. What do you understand by the term “greenhouse” effect? 

    2. With clear explanations, explain why it is called the “greenhouse” effect? 

    3. From your own reasoning and understanding, why do you think Environmental experts have become worried about the greenhouse effect?


    Activity 2.7

    Having discussed the intensity of Sun’s radiation reaching the earth and the black body radiation theory, discuss the following questions: 

    • What are the effects of these radiations on the earth and its atmosphere after absorption and reflection?

    • From your own understanding, what would happen if there is imbalance between the absorbed and radiated energy in the earth’s atmosphere.

    • Can that incidence be avoided? How? Write in your own words all the scientific measures that can be done to avoid that kind of situation.

    Activity 2.8:

                                                                          Fig.2. 7:From the picture above, 

    1. What do you observe from the picture above? 

    2. What could be the major causes of such situation in most of the communities especially in Rwanda? 

    3. How does this situation affect the welfare of the people in a given community? 

    4. In your view, suggest the preventive practices people should do to avoid such situations?

    2.4.1 Climate change and related facts 

    There has been variation in the atmospheric conditions in a given time. This has affected the seasons leading to a less output of our produce especially from agriculture, fishing and other activities. These changes are sometimes for a short time but also may take a long time. Some of these changes result from our practices like farming, industrialization, urbanization, mining and other infrastructure developments. Care should be taken so as these changes in the atmospheric conditions can be avoided.

    Activity 2.9 

    1.From your experience, have you ever experienced changes in atmospheric conditions? How long did it take?  

    2. In your own views discuss the causes of those changes. Are these changes harmful or useful?  Explain your reasoning 

    3. As a member of the community discuss how you identify that there is climatic change 

    4. If an investor wants to start an agricultural farm in your community. Depending on related reality of climatic conditions of your area, what advices and information would you give to that investor?

    Climate is usually defined as the “average weather,” or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands of years. The classical period is 3 decades, as defined by the World Meteorological Organization (WMO).These quantities are most often surface variables such as temperature, precipitation, and wind. Weather is measured in terms of the following parameters: wind, temperature, humidity, atmospheric pressure, cloudiness, and precipitation. In most places, weather can change from hour-to-hour, day-to-day, and season-toseason. Climate can be described as the sum of weather. While the weather is quite variable, the trend over a longer period, the climate, is more stable. 

    However climate change can be observed over a longer period of time. Climate change refers to any significant change in the climate parameters such astemperature, precipitation, or wind patterns, among others, that occur over several decades or longer Natural and human systems have adapted to the prevailing amount of sunshine, wind, and rain. While these systems can adapt to small changes in climate, adaptation is more difficult or even impossible if the change in climate is too rapid or too large. This is the driving concern over anthropogenic, or human induced, climate change. If climate changes are too rapid then many natural systems will not be able to adapt and will be damaged and societies will need to incur the costs of adapting to a changed climate (REMA)

    Some of important terms we need to know 

    • Climate feedback: This refers to a process that acts to amplify or reduce direct warming or cooling effects. 

    • Climate lag: This is the delay that can occur in a change of some aspect of climate due to the influence of a factor that is slow acting. 

    • Climate model: This is a quantitative way of representing the interactions of the atmosphere, oceans, land surface, and ice. Models can range from relatively simple to quite comprehensive

    This explains a delay that occurs in climate change as a result of some factors that changes only very slowly. For example, the effects of releasing more carbon dioxide into the atmosphere occur gradually over time because the ocean takes a long time to warm up in response to these emissions. 

    Project work 2.2: 

    1. Using a case study of Rwanda, by identifying different areas or provinces, Design a good chat that may be in tabular form showing differences in the amounts of sunshine, rainfall, humidity and precipitation in those areas or provinces. 

    2. Still using your findings, what has led to the difference in the climate changes in these areas yet they are all found in Rwanda? 

    3. Compare and contrast the climate of these provinces 

    4. Make a compressive report. You can share it with your friends and finally to the teacher.

    2.4.2 Causes of climate change.


    Read the text below and answer the questions that follow.

    In Rwanda, like in many other developing countries, large efforts are being invested in reducing vulnerability to climate change by taking actions needed to increase preparedness for climate change, including specific interventions (such as larger storm drains or new crop varieties) and also broader social economic strategies (such as relocating households from high risk zones). This is called adaptation to climate change. The terminology of “Climate resilience” is usually used to describe a broader agenda than adaptation as described above. It captures activities which build the ability to deal with climate variability – both today and in the future. Among other causes, the concentration of green gases in the atmosphere greatly affects the temperature of the Earth. 


    1. Explain the meaning of the underlined terms in the text 

    2. From the text above, what is the major cause of climate change 

    3. Discuss some of the strategies that the Rwandan Government is doing to fight the problem of the climate change. State some of the actions taken as described in the text 

    4. The writer in the text talked about industrialization as a practice that can lead to climate change. From your understanding and experience, how is this possible?

    Physics behind climate change and causes

    The climate of the earth is controlled by its absorption and the subsequent emission of that energy. The Earth’s surface temperature is determined by the balance between the absorption and emission of Sun’s radiation. 

    The major cause of climate change is the concentration of greenhouse gases, especially water vapor and carbon dioxide. These gases trap thermal radiation from the earth’s surface and this effect keeps the surface warmer than it would be. Human activities are major factors that lead to natural greenhouse effect. 

    Most of activities done by human lead to high concentration of greenhouse gases. From research it has been found that the concentration of carbon dioxide has risen by about 30% in this era as compared to pre-industrial era. This gives a projection that the concentration of these greenhouse gases is still increasing day and night as people continue using fossil fuels. Such activities include bush burning, burning of fossil fuels, deforestation and agriculture. 

    All these activities have a strong impact on the climate of a given area as they may lead to either warming or cooling the land. 

    On another hand, industries have also led to the change in climatic conditions as they emit carbon gases into the atmosphere. From what is happening currently, the climatic conditions are worsening if the world becomes more industrialized. 

    Man is trying to limit this by making machines that emit less carbon gases (REMA)


                                                                    Fig.2. 8 An operating industry giving out gases

    These gases affect the atmosphere that leads to climate change. Note: It is very important to have to work and do different activities that may lead us to develop and our country too. But care should be taken NOT to destroy the Nature. 

    Activity 2.11: 

    1. What do you think are the factors that lead climatic change in your area? Make a general conclusion using a case study of Rwanda.

    2. The earth’s climate can be affected by natural factors that are external to the climate system, such as changes in volcanic activity, solar output, and the earth’s orbit around the sun. How can people limit these factors to have a better climate? Share with your friends and even the teacher.

    2.4.3 Checking my progress

    1. What do you understand by the following terms as used in this concept? 

        a. Weather 

        b. Climate

        c. Humidity

        d. Temperature 

        e. Climatic change 

    2. Using Physics Concepts, discuss why different areas found in the same region may have different climatic conditions. 

    3. What are some of the strategies as a Rwandan have you set to fight these changes? 

    4. Plan and write an essay about climatic changes in Rwanda. 

    5. Study the graph given below and answer the questions that follow


    Fig.2. 9 Variation of the annual average temperature in 0C (1971-2009) at Kigali station Airport and Kamembe Airport Station (Source: Data analysis provided by the Rwanda meteorological service) (REMA)

       a. From the graph, which station had higher temperature? Explain why the selected station show high values of temperature relating to the factors that affect climate. 

       b. What was the recorded temperature of the two stations in 2005? 

       c. Discuss with relevant examples why there is a need to record temperatures of a given place after a given time. 

    6. Let’s have our minds rest using physics Below is a crossword puzzle about climatic change. Check the left of the puzzle and find the corresponding word in the puzzle


    What you can do to save your/our climate 

    • Learn about climate change share knowledge and information on climate change. By sharing knowledge and strategies to combat climate change with others you will increase awareness on climate change issues. Talk with your colleagues and leadership about how you can better integrate climate change considerations; 

    • Learn about how climate change impacts your sector. By looking into the negative impacts of climate change on your business processes and coming up with adaptation solutions you will make it climate-proof and reduce your sector’s vulnerability to climate change.


    2.5.1 Climate change mitigation

    Activity 2.13: Read and Contribute 

    The government of Rwanda is trying to sensitize people not to cut down trees for charcoal, Drying wetlands for farming activities and regulating people from approaching wetlands, forests (Both Natural and artificial) and Fighting all activities that may lead to climate change. 

    a. As a good citizen of Rwanda, Do you support these plans of the government? Support your stand with clear justifications 

    b. If Yes what have you done to implement some of these policies? 

    c. What are some of the New Technologies that the government is advocating for to stop these negative climate changes?

    Climate change mitigation refers to efforts to reduce or prevent emission of greenhouse gases. Mitigation can mean using new technologies and renewable energies, making older equipment more energy efficient, or changing management practices or consumer behavior (IPCC, 1996). 

    Climate change is one of the most complex issues we are facing today. It involves many dimensions science, economics, society, and moral and ethical questions and is a global problem, felt on local scales that will be around for decades and centuries to come. Carbon dioxide, the heat-trapping greenhouse gas that has driven recent global warming, lingers in the atmosphere for centuries, and the earth (especially the oceans) takes a while to respond to warming. 

    So even if we stopped emitting all greenhouse gases today, global warming and climate change will continue to affect future generations. In this way, humanity is “committed” to some level of climate change.  

    Because we are already committed to some level of climate change, responding to climate change involves a two-pronged approach: 

    Reducing emissions and stabilizing the levels of heat-trapping greenhouse gases in the atmosphere (“mitigation”); Adapting to the climate change already in the pipeline (“adaptation”).

    2.5.2 Mitigation and adaptation


                           Fig.2. 10: Solar panels have been used to reduce some of the problems caused by other sources of energy 

    Because of these changes in climatic conditions, man has devised all possible measures to see how he can live in harmony on this planet. This has made man to think harder so that these green gases can be minimized. 

    The process of preventing all these greenhouse gases is what is known as mitigation. This is very important as it is aimed at controlling the rise in temperatures of the earth while regulating earth’s temperature. 

    The main goal of mitigation is to reduce human interference to nature thereby stabilizing the greenhouse gas levels in a given time to allow ecosystem to adapt naturally to the climate changes. Care should be taken while these adjustments are made not to affect food production and other economic developments. 

    Among other strategies, mitigation strategies include retrofitting buildings to make them more energy efficient; adopting renewable energy sources like solar, wind and small hydro-electric plants helping cities develop more sustainable transport such as bus rapid transit, electric vehicles and bio fuels, promoting more sustainable uses of land and forests and creating carbon sinks like in big oceans in case there are no alternatives.


    Goal: To construct your control greenhouse model and your enhanced greenhouse model, begin by collecting all the materials other than the dry ice. 




    1. Prepare the enhanced greenhouse model, 

    2. Use a flame from the candle to heat the end of a paper clip. 

    3. Use the hot paper clip to make a small hole in the side of one of the plastic drinking bottles. 

    4. Make this hole about half way between the top and bottom of the bottle. 

    5. Make sure that the plastic tubing will fit into the hole. 

    6. Put 200 ml of distilled water into each of the two bottles. 

    7. Place the plastic tubing into the hole that you made for the “enhanced greenhouse” effect model. 

    8. Use clay to prevent any air from leaking out once the experiment begins. 

    9. Place a thermometer into the top of each bottle so that the end of the thermometer is in the centre of the bottle. 

    10. Hold in place and seal off the bottle top opening using the modelling clay. 

    11. Prepare the container for inserting the dry ice vapor, obtain two Styrofoam cups. One should be larger than the other or you can cut one to fit beneath the other. 

    12. Punch a hole in the bottom of the larger cup on the top. 

    13. Insert the plastic tubing and use the clay to prevent any leakage of the carbon dioxide.

    14. Obtain a piece of dry ice that fits into the smaller Styrofoam cup. 

    15. Add enough water to begin sublimation. 

    16. Connect the plastic tubing to the bottle and let the carbon dioxide gas to flow into the bottle for 90 seconds. 

    17. Take the tubing out and close the tubing hole with clay once you have added the carbon dioxide. 

    18. Place both bottles the same distance from a heat lamp and turn on the light 

    19. Begin recording the temperature as soon as you have closed the hole and turn on the light. Record the temperature every two minutes for twenty minutes in the table. 

    20. Construct a graph of your data. 

    2.5.3 Checking my progress

    The graph below shows the emission of Carbon emissions from fossil fuels of a certain region in Africa from 1990 to 2014. Study the graph carefully and answer the questions that follow


                                Fig.2. 11 Global carbon emission from fossil fuels, 1900-2010 (REMA)

    1. By observing clearly the graph, explain the trend of the Curve from 1990 to 2010. With the knowledge and ideas you have acquired from this Unit, Discuss factors that might have led to the rise of the shape of the graph 

    2. Suppose the Curve was to be extended to 2018, do you think the curve would continue the trend or would Fall? Explain your reasoning 

    3. Discuss some of the major causes of increased carbon emissions in our Society, 

    4. Come up with possible measures that can assist the community to have less 


    2.6.1 Multiple choice type questions. 

    Re-write the questions below in your notebook and CIRCLE the best alternative 

    1. The emissivity (ε) can be defined as the ratio of 

     a. Emissive power of real body to the emissive power of black body 

     b. Emissive power of black body to the emissive power of real body 

     c. Reflectivity of real body to emissive power of black body 

     d. Reflectivity of black body to emissive power of real body. 

    2. Imagine two planets. Planet A is completely covered by an ocean, and has and overall average albedo of 20%. Planet B is blanketed by clouds, and has an overall average albedo of 70%. Which planet reflects more sunlight back into space? 

     a. Planet A 

     b. Planet B 

     c. The two planets reflect the same amount of light 

     d. More information is needed to answer this question 

    3. _______________ is a term used to a process that acts to amplify or reduce direct warming or cooling effects 

     a. Climate change  

     b. Weather

     c. Climate feedback

     d. Climate model 

    4. The filament of an electric bulb has length of 0.5 m and a diameter of 6x10-5 m. The power rating of the lamp is 60 W Assuming the radiation from the filament is equivalent to 80% that of a perfect black body radiator at the same temperature. The temperature of the filament is (Stefan Constant is 5.7x10-8 Wm-2K-4):

      a. 1933 K

      b. 796178.3 K

      c. 64433333.3 K

      d. 60 K 

    5 .The long-term storage of carbon dioxide at the surface of the earth is termed as 

      a. Black body radiation   

      b. Thermal expansion 

      c. Solar radiation management

      d. Sequestration 

    6. The balance between the amount of energy entering and exiting the Earth system is known as 

      a. Radiative balance

      b. Paleoclimatology

      c. Black body Radiation

      d. Solar radiation 

    7. The following are examples of green gases except 

       a. Carbon dioxide

       b. Nitrous oxide

       c. Methane

       d. Oxygen 

    8. The government of Rwanda is advising the people to conserve the nature. This is intended to limit the incidence of rise in the temperature. This conservation of nature

      a. Reduces the amount of water vapor that leads to increase in temperature

      b. Reduces the amount of Carbon dioxide in the space

      c. Increases the amount of plant species that is required to boost our tourism industry 

      d. Provides a green environment for human settlement 

    2.6.2 Structured questions 

    1. a.  State Wien’s displacement law and its practical implications     

        b.  Use the graph indicated below to answer the questions that follow


     I. What does the graph explain?

     II. Explain the spectrum that is found between temperatures of  4000 and 7000  K

     III. Why do you think the three curves have different shapes 

    2. Discuss any 4 main reasons that brings about variation of sun’s Intensity 

    3.a. Calculate the albedo of a surface that receives 15000 Wm-2 and reflects 15 KW.m-2 Comment on the surface of that body

       b. Discuss some of the scientific factors that affect planets Albedo 

    4.a. What do you understand by the following terms? 

       I. Climate change as applied in physics

       II. Greenhouse Effect

       b. With Clear explanations, discuss how Greenhouse effect can be avoided 

    2.6.3 Essay type questions 

    1. Clemance a year 4 student in the faculty of engineering in University of Rwanda found out in her research that a strong metal at 1000k is red hot while at 2000k its white hot. Using the idea of black body, explain this observation. 

    2. John defined black body as anybody that is black. Do you agree with his definition? If YES why? and if NOT why not? Also sketch curves to show the distribution of energy with wavelength in the radiation from a black body varies with temperature.

    3. An electric bulb of length 0.6 m and diameter 5 x 10-5 m is connected to a power source of 50 W. Assuming that the radiation from the bulb is 70% that of a perfect black body radiator at the same temperature, Estimate the steady temperature of the bulb. (Stefan’s constant = 5.7 x 10 - 8 W m 2 K-4.) 

    4. Write short notes about greenhouse effect and explain all its effects. 

    5. What do you understand by the term green gases? How do these gases contribute to the global warming?

    6. REMA is always advising people to plant more trees and stop cutting the existing ones. Using scientific examples, explain how this is aimed at controlling global warming 

    7. Explain climate change mitigation and explain why it’s important. 

    8. Explain what happens to most radiation that is absorbed by the surface of earth? 

    9. Is there difference between sensible and latent heat? 

    10. Write short notes on the following terms as applied in climate change 

      I. Climate feedback  

      II. Climate lag 

      III. Climate model    

    11. Plan and write a good composition about causes of climate change and how it can be controlled. (Your essay should bear introduction, body and conclusion)