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7.37.3 What are theWhat are the causes of globalcauses of global warming?warming?
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What will happen to the insolation that reaches the earth’s surface?
9 unitsSolar radiation reflected by the earth’s surface
49 unitsSolar 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
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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.
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The atmosphere
Some radiation is released back into space
DustWater 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
radiationSome 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
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The atmosphere
Some radiation is released back into space
DustWater 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
radiationSome 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 19th century.
Why?
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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)
Methane (CH4)
Nitrous oxide (N2O)
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What are greenhouse gases?1 Carbon 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
Respiration
Photosynthesis
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?
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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.)
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What are greenhouse gases?3 Nitrous oxide
Oceans are a source of nitrous oxide
Nitrous oxide is released naturally from oceans and by bacteria in soils.
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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 dioxide Methane
Nitrous oxide Since 1800, the concentration of the three greenhouse gases in the atmosphere has been ( decreasing / increasing ).
Why?
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What are the human activities that intensify the greenhouse effect?1 Burning of fossil fuels
Respiration
PhotosynthesisCombustion of fossil fuels
RespirationPhotosynthesis
Human activity has
disturbed the carbon cycle.
Factories, power plants and vehicles emit large amounts of carbon dioxide.
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What are the human activities that intensify the greenhouse effect?2 Deforestation
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.
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What are the human activities that intensify the greenhouse effect?3 Agriculture
How does agriculture intensify the
greenhouse effect?
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What are the human activities that intensify the greenhouse effect?3 Agriculture
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 Fooddemand
Agriculturalactivities
Release ofgreenhousegases
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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)
4 Garbage treatment
An incinerator
Carbon dioxide and nitrous oxide are emitted when garbage is burnt in the incinerators
(Credit: Panorama Stock Photo Co. Ltd.)
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What are the human activities that intensify the greenhouse effect?5 Industrial activities
Manufacturing has produced man-made greenhouse gases in the atmosphere.
Chlorofluo-rocarbons
(CFCs)
Hydrofluo-rocarbons
(HFCs)
Perfluoroc-arbons (PFCs)
Sulphur hexafluori-
de (SF6)
Nitrous oxides (N2O)
Production of foams, refrigerants and solventsAluminium smelting and magnesium productionProduction of nylon
Foam products
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Why should we care about the amount of greenhouse gases in the atmosphere?
Greenhouse gases Lifetime (years)
Carbon dioxide 5-200Methane 12Nitrous oxide 114CFCs 10-over 100HFCs 260
PFCs 10,000-over 50,000
SF6 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.
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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
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1 Changes 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 Earth
Nearly circular orbit
Elliptical orbit
Sun 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 ).
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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.
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)
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2 Changes in the tilt of the earth’s axisChanges 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
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2 Changes in the tilt of the earth’s axisChanges 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
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2 Changes in the tilt of the earth’s axisHow do changes in
obliquity affect polar regions?
Obliquity
High Low
( 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
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3 Amount of aerosols in the atmosphereAerosols 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)