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II. Is the greenhouse effect human enhanced?II. Is the greenhouse effect human enhanced?II. Is the greenhouse effect human enhanced?II. Is the greenhouse effect human enhanced?1. What is the greenhouse effect?1. What is the greenhouse effect?

Greenhouse is:• a house made of glass

• allows sunlight (solar energy) to enter it

• but does not allow all the heat energy inside to escape

Sunlight enters the greenhouse through

the windows

The ground is heated

Heat energy cannot pass through the windows

Heat energy reflects to the ground and keeps the

greenhouse warm inside

The ground emits heat to warm the air


It creates a higher average temperature It creates a higher average temperature inside than outside the structureinside than outside the structure It creates a higher average temperature It creates a higher average temperature inside than outside the structureinside than outside the structure


• The earth’s atmosphere functions like a greenhouse

• Because water vapour and atmospheric gases absorb tabsorb t

errestrial radiationerrestrial radiation• This is known as the greenhouse effectgreenhouse effect

Sun

Solar energy passes through the atmosphere

Greenhouse gases in the atmosphere trap

some of the heat

Some of the sun’s energy is reflected back into space


The greenhouse effect is thus

a natural processnatural process


2. What are greenhouse gases?2. What are greenhouse gases?

• The two greenhouse gases with the largest concentraThe two greenhouse gases with the largest concentration in the atmosphere are tion in the atmosphere are water vapourwater vapour and and carbon carbon dioxidedioxide

• Over 95% of the greenhouse effect is the result of atOver 95% of the greenhouse effect is the result of atmospheric water vapour in the earth’s atmospheremospheric water vapour in the earth’s atmosphere

• The two greenhouse gases with the largest concentraThe two greenhouse gases with the largest concentration in the atmosphere are tion in the atmosphere are water vapourwater vapour and and carbon carbon dioxidedioxide

• Over 95% of the greenhouse effect is the result of atOver 95% of the greenhouse effect is the result of atmospheric water vapour in the earth’s atmospheremospheric water vapour in the earth’s atmosphere


• Water droplets in clouds Water droplets in clouds reflectreflect sunlight sunlight

• Greenhouse warmingGreenhouse warming moderates the nighttime moderates the nighttime low temperatures, but will not increase the low temperatures, but will not increase the daytime high temperaturesdaytime high temperatures

• Water droplets in clouds Water droplets in clouds reflectreflect sunlight sunlight

• Greenhouse warmingGreenhouse warming moderates the nighttime moderates the nighttime low temperatures, but will not increase the low temperatures, but will not increase the daytime high temperaturesdaytime high temperatures


The amount of carbon dioxide in the atmosphere is The amount of carbon dioxide in the atmosphere is

controlled by the natural controlled by the natural carbon cyclecarbon cycle


Green plants take up carbon dioxide

during the day in photosynthesisphotosynthesis and release it at night

Green plants take up carbon dioxide

during the day in photosynthesisphotosynthesis and release it at night


Animals also release carbon dioxide in Animals also release carbon dioxide in respirationrespiration


Exchange of carbon dioxide also takes place between the atmosphereatmosphere and the oceanocean by:

• Photosynthesis and respiration of algae and sea animals

• Absorption of carbon dioxide by seawater


There is a There is a balancebalance of of carbon dioxide in the carbon dioxide in the natural environmentnatural environment


Oil, coal and natural gas are Oil, coal and natural gas are fossil fuelsfossil fuels

Gas pipe

Coal

Oil drilling


Human activitiesHuman activities such as power such as power generation, manufacturing and generation, manufacturing and transportation release large amounts transportation release large amounts of carbon dioxide through the of carbon dioxide through the combustion of fossil fuelscombustion of fossil fuels


• It takes time for the natural It takes time for the natural environment to absorb this environment to absorb this added and ongoing input of added and ongoing input of carbon dioxidecarbon dioxide

• There has been an There has been an increase increase of carbon dioxide in the of carbon dioxide in the atmosphereatmosphere

• It takes time for the natural It takes time for the natural environment to absorb this environment to absorb this added and ongoing input of added and ongoing input of carbon dioxidecarbon dioxide

• There has been an There has been an increase increase of carbon dioxide in the of carbon dioxide in the atmosphereatmosphere


• Production and transportation Production and transportation of coal, natural gas and oilof coal, natural gas and oil

• Decomposition of organic Decomposition of organic wasteswastes

• Rearing of livestockRearing of livestock

Sources ofSources of methanemethane::


• Agricultural and industrial activities

• Combustion of solid waste and fossil fuels

Sources ofSources of nitrous oxidenitrous oxide::


There are other powerf

ul greenhouse gases whi

ch come from a variety

of industrial processes

•chlorofluorocarbons

•hydrofluorocarbons

•perfluorocarbons

•sulphur hexafluoride


Characteristics:

• concentrations are

comparatively low

• long-lived

• powerful warmers


3. What is the evidence for global warming?3. What is the evidence for global warming?

Global warming is the increase of the earth’s natural greenhouse effect which raises the average global temperature of the atmosphere near the earth’s surface


Green gases produced by Green gases produced by human activities human activities

Green gases produced by Green gases produced by human activities human activities

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• Melting of ice caps Melting of ice caps and floating ice at and floating ice at the earth’s poles the earth’s poles

• An average global sea-level An average global sea-level

rise of 10-25 cm over the rise of 10-25 cm over the

past 100 yearspast 100 years

Other evidence of global warming includes:Other evidence of global warming includes:


• Northward migration Northward migration of some warm-climate of some warm-climate fish and tree speciesfish and tree species

• Retreat of glaciers Retreat of glaciers on the top of high on the top of high mountainsmountains


Scientists predict an increase in the Scientists predict an increase in the average global surface temperature of average global surface temperature of 0.6-2.5 over the next fifty years and ℃0.6-2.5 over the next fifty years and ℃up to 1.4 to 5.8 in the next century℃up to 1.4 to 5.8 in the next century℃


Melting of ice capsMelting of ice capsMelting of ice capsMelting of ice caps

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