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8.5 Earth’s climate is powered by energy from the Sun. The interactions between the Sun and Earth’s air, land, liquid water, ice, and living things play a role in producing Earth’s climate. Solar Energy ▶▶ solar energy: energy from the Sun ▶▶ radiation: any energy that travels in the form of waves Solar energy is energy that comes from the Sun. Almost all processes on Earth are ultimately powered by solar energy. Solar energy is a type of radiation. Radiation is energy that is emitted or transmitted in the form of waves. Solar energy has a range of energy levels, which can be divided into visible light, ultraviolet light, and infrared radiation (Figure 1). These different types of radiation have different energy levels. dig deeper Ultraviolet Light The high energy of ultraviolet (UV) light enables it to penetrate skin, which is why it can cause sunburn. Energy output Did You Know? Ultraviolet (short wavelength, high energy) Visible Infrared (long wavelength, low energy) Wavelength Figure 1 Solar energy is made up of waves that have different energy levels. Different Regions on Earth Receive Different Amounts of Solar Energy An important natural factor in determining climate is how much solar energy a region receives, and how that amount of solar energy changes over time. The next subsections will describe some factors that affect the amount of solar energy received by regions on Earth. 308 Chapter 8 • Earth’s Climate System NEL TRY This spreading out Skills: Performing, Observing, Analyzing 3.A., 3.B. 3.Have one person hold the cardboard at a 45º angle to the light beam. Have a second person use a different-coloured pen to trace the shadow on the graph paper. In this activity, the flashlight beam represents a beam of sunlight. The cardboard represents a 1 km2 area on Earth’s surface. Equipment and Materials: 15 cm 15 cm piece of cardboard; graph paper; transparent tape; flashlight; two different-coloured pens A.Compare the two shadows produced in Steps 2 and 3. T/I 1.Tape the graph paper to a wall. Then, shine the flashlight on the paper and change your position until the light beam forms a clear circle. B.In which position did the cardboard block the most light? T/I C.Remember that the size of the cardboard represented the same area of land. In which position (at the equator or the poles) would the land be warmer? T/I 2.Have one person hold the cardboard at a 90º angle to the light beam. Have a second person trace the shadow that appears on the graph paper. Latitude Latitude is the distance north or south of Earth’s equator, measured as an angle. Figure 2 shows how latitude affects the amount of solar radiation that different places on Earth’s surface receive. ▶▶ latitude: the angular distance north or south of Earth’s equator, measured in degrees • At lower latitudes (closer to the equator), solar radiation hits Earth’s surface almost straight on. This solar energy is concentrated in a smaller area. (See the red lines in Figure 2(a).) • At higher latitudes (farther from the equator), solar radiation hits Earth’s surface at a larger angle. This solar energy is spread across a larger area. (See the red lines in Figure 2(b).) (a) energy from the Sun r ato equ (b) North Pole energy from the Sun r ato equ South Pole Figure 2 (a) At lower latitudes, incoming solar energy does not spread out very much. (b) At higher latitudes, incoming solar energy spreads out. NEL 8.5 Natural Factors That Affect Climate 309 Earth’s Tilt and Orbit Figure 3 shows Earth’s orbit around the Sun. Earth is drawn so that the poles are not straight up and down, because our planet is tilted. As Earth moves around the Sun, this tilt dramatically affects the amount of solar energy that different regions receive. For example, during our summer, the North Pole is tilted toward the Sun. Canada, therefore, receives more solar energy in summer, when we have warmer weather (Figure 4(a)). During our winter, the North Pole is tilted away from the Sun. Canada then receives less solar energy, so our winters are colder (Figure 4(b)). The tilt has more of an effect on seasonal changes in climate than the distance of Earth from the Sun. (a) (b) Figure 3 Earth’s tilt has a greater effect on climate than its orbit. Climate Change and Earth’s Motion Figure 4 Earth’s tilt affects our seasons. We can enjoy (a) canoeing in the summer months, and (b) tobogganing in the cold winter months. In 1941, scientist Milutin Milankovitch developed a theory to explain the ice ages in Earth’s history (Figure 5). He suggested that the cycles of ice ages are caused by three factors: •Shape of Orbit: Earth’s orbit changes shape from more circular to less circular over a period of about 400 000 years. Earth gets up to 23 % more solar energy at the closest distance compared to the farthest distance. • Tilt: Earth’s tilt varies over about 41 000 years from 22.1° to 24.5°. As the tilt changes, the seasons also change. • Wobble: As Earth spins, it slowly wobbles around on its axis. The wobble causes Earth’s axis to change the direction it points to. One complete wobble takes about 26 000 years. 310 Chapter 8 • Earth’s Climate System NEL Together, these changes cause the regular patterns of ice ages and warmer periods. Climate scientists think that these patterns are the main cause of the 100 000-year cycles in Earth’s climate. However, these take place too slowly to be responsible for recent global warming. wobbling of the axis Earth’s orbit Sun tilt changing shape of orbit changing tilt Figure 5 Natural causes of Earth’s ice ages and warming periods 8.5 Wrap Up • Earth’s climate is powered by solar energy. • Latitude affects how intense the sunlight is at a particular location. • The seasons are the result of Earth’s tilt and orbit. • Long-term cycles in Earth’s climate are caused by changes in the shape of Earth’s orbit and tilt, and Earth’s wobble. Check Your Learning 1.Describe the range of energy levels given off by the Sun. K/U 5.What do you think Earth’s climate would be like if it had a circular orbit and no tilt? A 2.List three possible causes of long-term climate change. K/U 6.(a) Why are the seasons important to you? (b) Using a method of your choosing, describe how your life would be different if you lived somewhere with dry and rainy seasons. You may be able to answer this question from your own life story. C A 3.Explain why a city in Canada experiences winter at the same time as a city in South America experiences summer. K /U 4.Compare the Sun’s energy that reaches the equator to the Sun’s energy that reaches the areas nearer the poles. Draw diagrams to support your answer. K/U C NEL 7.Which has a greater effect on Canada’s seasonal climate changes—Earth’s tilt or Earth’s orbit? K/ U 8.5 Natural Factors That Affect Climate 311