© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 7.3What are the causes of global causes of global warming? warming?

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What will happen to the insolation that reaches the earth’s surface? 9 units Solar radiation reflected by the earth’s surface 49 units Solar radiation absorbed by the earth’s surface Only ____ units of solar radiation reaches the earth’s surface 58 As the insolation reaches the earth’s surface, 9 units of it is reflected to space The remaining 49 units of it is absorbed by the earth’s surface The absorbed energy heats up the earth’s surface

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What will happen to the insolation that reaches the earth’s surface? 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 The earth’s average temperature remains relative stable since solar radiation will eventually leave the earth in the same amount as it comes in.

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit The atmosphere Some radiation is released back into space Dust Water vapour Greenhouse gases A lot of solar radiation enters and passes through the atmosphere 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 As heat is retained, the atmosphere is kept warm What will happen to the insolation that reaches the earth’s surface? The insolation reaches the earth’s surface The earth’s surface heats up Greenhouse gases act as a blanket and keep the lower atmosphere warm. This is know as ________________. greenhouse effect

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit The atmosphere Some radiation is released back into space Dust Water vapour Greenhouse gases A lot of solar radiation enters and passes through the atmosphere 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 As heat is retained, the atmosphere is kept warm What will happen to the insolation that reaches the earth’s surface? The insolation reaches the earth’s surface The earth’s surface heats up The average temperature of the earth’s surface has gone up since the late 19 th century. Why?

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 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 (CO 2 ) Methane (CH 4 ) Nitrous oxide (N 2 O)

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What are greenhouse gases? 1Carbon dioxide Carbon dioxide is the principal greenhouse gas in terms of the greenhouse effect. It circulates around the earth in the carbon cycle. Combustion Respiration Photosynthesis Carbon dioxide When carbon dioxide reaches the atmosphere, it is captured, transformed and stored mainly in the oceans and through photosynthesis. How does deforestation affect the carbon cycle?

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What are greenhouse gases? 2Methane 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.)

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What are greenhouse gases? 3Nitrous oxide Oceans are a source of nitrous oxide Nitrous oxide is released naturally from oceans and by bacteria in soils.

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What are the human activities that intensify the greenhouse effect? The graphs show the changes in the concentration of the greenhouse gases in the atmosphere. Carbon dioxideMethane Nitrous oxide Since 1800, the concentration of the three greenhouse gases in the atmosphere has been ( decreasing / increasing ). Why?

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What are the human activities that intensify the greenhouse effect? 1Burning of fossil fuels Respiration Photosynthesis Combustion of fossil fuels Respiration Photosynthesis Human activity has disturbed the carbon cycle. Factories, power plants and vehicles emit large amounts of carbon dioxide.

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What are the human activities that intensify the greenhouse effect? 2Deforestation A cleared site after deforestation Deforestation through the burning of trees releases carbon dioxide. Fewer trees are available for absorbing the extra amount of carbon dioxide from the atmosphere. The increased carbon dioxide in the atmosphere will disturb the carbon cycle.

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What are the human activities that intensify the greenhouse effect? 3Agriculture How does agriculture intensify the greenhouse effect?

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What are the human activities that intensify the greenhouse effect? 3Agriculture Burning organic waste and cattle breathing release carbon dioxide. Paddy growing and the digestive process of cattle release methane. The use of nitrogen fertilizers releases nitrous oxide. How does rapid population growth intensify global warming? Population Food demand Agricultural activities Release of greenhouse gases

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What are the human activities that intensify the greenhouse effect? People produce enormous amount of garbage every day, while most of the garbage goes into landfills and incinerators. Methane is released when garbage decomposes in the landfills A landfill in Phnom Penh, Cambodia (Credit: Ng Kim Hung) 4Garbage treatment An incinerator Carbon dioxide and nitrous oxide are emitted when garbage is burnt in the incinerators (Credit: Panorama Stock Photo Co. Ltd.)

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What are the human activities that intensify the greenhouse effect? 5Industrial activities Manufacturing has produced man- made greenhouse gases in the atmosphere. Chlorofluo- rocarbons (CFCs) Hydrofluo- rocarbons (HFCs) Perfluoroc- arbons (PFCs) Sulphur hexafluori- de (SF 6 ) Nitrous oxides (N 2 O) Production of foams, refrigerants and solvents Aluminium smelting and magnesium production Production of nylon Foam products

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit Why should we care about the amount of greenhouse gases in the atmosphere? Greenhouse gases Lifetime (years) Carbon dioxide5-200 Methane12 Nitrous oxide114 CFCs10-over 100 HFCs260 PFCs 10,000-over 50,000 SF 6 3,200 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.

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 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

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 1Changes in the shape of the earth’s orbit 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. Earth Nearly circular orbit Elliptical orbit Sun The shortest distance The longest distance 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 ).

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 2Changes 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. Changes in the angle of the earth’s axis At present, the earth is tilted at an angle of ______ to the vertical. 23.5° (Credit: NASA)

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 2Changes in the tilt of the earth’s axis Changes in obliquity influence the intensity of insolation received in different seasons. This situation is more obvious at high-latitude regions. High obliquity (24.4°) Larger angle of the sun Low obliquity (10°) The ( lower / higher ) the obliquity, the stronger the summer sun. 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

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 2Changes in the tilt of the earth’s axis Changes in obliquity influence the intensity of insolation received in different seasons. High obliquity (24.4°)Low obliquity (10°) 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. The higher the obliquity, the ( weaker / stronger ) the winter sun. Therefore, high obliquity results in ( smaller / larger ) temperature difference between winter and summer. Winter Smaller angle of the sun

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 2Changes in the tilt of the earth’s axis How do changes in obliquity affect polar regions? Obliquity HighLow ( Less / More ) insolation received in summer in polar regions ( Cooler / Warmer ) summers in polar regions Melting of ice sheets ( Less / More ) insolation received in summer in polar regions ( Cooler / Warmer ) summers in polar regions Glaciation

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 3Amount 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. The 1980 eruption of Mount St Helens, the USA For example, during volcanic eruptions, a large amount of ash, dust and gases are ejected into the air (Credit: Gary Braasch/Corbis)