7.3 What are the causes of global warming?

1. 7.3 What are the causes of global warming?

2. What will happen to the insolation that reaches the earth’s surface? As the insolation reaches the earth’s surface, 9 units of it is reflected to space Only ____ units of solar radiation reaches the earth’s surface 58 9 units Solar radiation reflected by the earth’s surface The absorbed energy heats up the earth’s surface The remaining 49 units of it is absorbed by the earth’s surface 49 units Solar radiation absorbed by the earth’s surface

3. What will happen to the insolation that reaches the earth’s surface? The earth’s average temperature remains relative stable since solar radiation will eventually leave the earth in the same amount as it comes in. The heat at the earth’s surface is transferred into the atmosphere through conduction, convection and radiation and eventually leaves the earth Some heat is trapped by the greenhouse gases in the atmosphere and is re-radiated back to the earth’s surface

4. What will happen to the insolation that reaches the earth’s surface? Greenhouse gases act as a blanket and keep the lower atmosphere warm. This is know as ________________. greenhouse effect Some radiation is released back into space A lot of solar radiation enters and passes through the atmosphere Dust Water vapour Heat from the earth’s surface is released in the form of long wave radiation Some heat is absorbed and then re-radiated back to the earth’s surface Greenhouse gases The insolation reaches the earth’s surface The earth’s surface heats up As heat is retained, the atmosphere is kept warm The atmosphere

5. What will happen to the insolation that reaches the earth’s surface? The average temperature of the earth’s surface has gone up since the late 19th century. Why? Some radiation is released back into space A lot of solar radiation enters and passes through the atmosphere Dust Water vapour Heat from the earth’s surface is released in the form of long wave radiation Some heat is absorbed and then re-radiated back to the earth’s surface Greenhouse gases The insolation reaches the earth’s surface The earth’s surface heats up As heat is retained, the atmosphere is kept warm The atmosphere

6. How is the greenhouse effect being intensified? Greenhouse gases block the ( short / long ) wave radiation from leaving the earth. Some greenhouse gases are found naturally in the atmosphere Carbon dioxide (CO2) Nitrous oxide (N2O) Methane (CH4)

7. What are greenhouse gases? 1 Carbon dioxide How does deforestation affect the carbon cycle? Carbon dioxide is the principal greenhouse gas in terms of the greenhouse effect. Combustion Carbon dioxide Photosynthesis Respiration Photosynthesis It circulates around the earth in the carbon cycle. Respiration When carbon dioxide reaches the atmosphere, it is captured, transformed and stored mainly in the oceans and through photosynthesis.

8. What are greenhouse gases? 2 Methane Methane is produced when trees or leaves decompose in an environment where there is ( insufficient / sufficient ) oxygen. It is naturally produced in wetlands and oceans. Wetlands account for about 76% of global methane emissions from natural source (Credit: Biosphoto/Gunther Michel/Peter Arnold Inc.)

9. What are greenhouse gases? 3 Nitrous oxide Nitrous oxide is released naturally from oceans and by bacteria in soils. Oceans are a source of nitrous oxide

10. What are the human activities that intensify the greenhouse effect? Carbon dioxide Methane Nitrous oxide The graphs show the changes in the concentration of the greenhouse gases in the atmosphere. Since 1800, the concentration of the three greenhouse gases in the atmosphere has been ( decreasing / increasing ). Why?

11. What are the human activities that intensify the greenhouse effect? 1 Burning of fossil fuels Human activity has disturbed the carbon cycle. Photosynthesis Respiration Photosynthesis Combustion of fossil fuels Respiration Factories, power plants and vehicles emit large amounts of carbon dioxide.

12. What are the human activities that intensify the greenhouse effect? 2 Deforestation Deforestation through the burning of trees releases carbon dioxide. The increased carbon dioxide in the atmosphere will disturb the carbon cycle. Fewer trees are available for absorbing the extra amount of carbon dioxide from the atmosphere. A cleared site after deforestation

13. What are the human activities that intensify the greenhouse effect? 3 Agriculture How does agriculture intensify the greenhouse effect?

14. What are the human activities that intensify the greenhouse effect? 3 Agriculture How does rapid population growth intensify global warming? Burning organic waste and cattle breathing release carbon dioxide. Paddy growing and the digestive process of cattle release methane. Population Food demand The use of nitrogen fertilizers releases nitrous oxide. Release of greenhouse gases Agricultural activities

15. What are the human activities that intensify the greenhouse effect? 4 Garbage treatment Methaneis released when garbage decomposes in the landfills (Credit: Panorama Stock Photo Co. Ltd.) People produce enormous amount of garbage every day, while most of the garbage goes into landfills and incinerators. Carbon dioxide and nitrous oxide are emitted when garbage is burnt in the incinerators An incinerator A landfill in Phnom Penh, Cambodia (Credit: Ng Kim Hung)

16. What are the human activities that intensify the greenhouse effect? 5 Industrial activities Manufacturing has produced man-made greenhouse gases in the atmosphere. Foam products Production of foams, refrigerants and solvents Aluminium smelting and magnesium production Production of nylon

17. Why should we care about the amount of greenhouse gases in the atmosphere? Estimates of the lifetime of greenhouse gases in the atmosphere As greenhouse gases are released, they will stay in the atmosphere for a ( short / long ) time. That means greenhouse gases will continue to trap heat for a long time even if people stop emitting them.

18. Are there factors other than human activities leading to temperature change? Temperature change Changes in the shape of the earth’s orbit Changes in the tilt of the earth’s axis Amount of aerosols in the atmosphere

21. 1 Changes in the shape of the earth’s orbit Elliptical orbit Sun Sun The longest distance Nearly circular orbit The shortest distance Earth Earth The earth’s orbit goes from elliptical to nearly circular over a 100,000-year cycle The shape of the earth’s orbit changes during a cycle that spans about 100,000 years. When the orbit is most elliptical, the difference in the amount of solar radiation received by the earth between the nearest and the farthest approach of the earth to the sun will be the ( least / greatest ).

22. 2 Changes in the tilt of the earth’s axis The obliquity of the earth’s axis changes over time, ranging from about 22.8° to 24.4° and back over a cycle of about 41,000 years. At present, the earth is tilted at an angle of ______ to the vertical. 23.5° Changes in the angle of the earth’s axis (Credit: NASA)

23. 2 Changes in the tilt of the earth’s axis Changes in obliquity influence the intensity of insolation received in different seasons. Note: The difference in the degree of obliquity of the earth’s axis has been exaggerated in order to show the variation clearly. The earth does not tilt at 10° in reality. Summer This situation is more obvious at high-latitude regions. Larger angle of the sun High obliquity (24.4°) Low obliquity (10°) The ( lower / higher ) the obliquity, the stronger the summer sun.

24. 2 Changes in the tilt of the earth’s axis Changes in obliquity influence the intensity of insolation received in different seasons. Note: The difference in the degree of obliquity of the earth’s axis has been exaggerated in order to show the variation clearly. The earth does not tilt at 10° in reality. Winter Smaller angle of the sun Low obliquity (10°) High obliquity (24.4°) The higher the obliquity, the ( weaker / stronger ) the winter sun. Therefore, high obliquity results in ( smaller / larger ) temperature difference between winter and summer.

25. 2 Changes in the tilt of the earth’s axis Obliquity How do changes in obliquity affect polar regions? High Low ( Less / More ) insolation received in summer in polar regions ( Less / More ) insolation received in summer in polar regions ( Cooler / Warmer ) summers in polar regions ( Cooler / Warmer ) summers in polar regions Melting of ice sheets Glaciation

26. 3 Amount of aerosols in the atmosphere Aerosols are tiny particles suspended in the air. Most of the aerosols can reflect radiation back into space, therefore reducing the amount of energy reaching the earth’s surface. For example, during volcanic eruptions, a large amount of ash, dust and gases are ejected into the air The 1980 eruption of Mount St Helens, the USA (Credit: Gary Braasch/Corbis)