Unit 9G Lesson 4: Global Warming

Objective: to learn about the causes and effects of global

warming.

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The Earth’s Greenhouse

• Our atmosphere acts like a greenhouse.– Heat from the sun enters our atmosphere.– Some of this heat bounces off of the planet and

back into space as infra red rays– The rest of the heat is trapped by the earth and

the atmosphere.

• This is what keeps the Earth warm enough to support life.

• If it wasn’t for our atmosphere our planet would be a frozen wasteland.

Greenhouse Gases

• Greenhouse gases are the gases in the atmosphere which trap the sun’s heat.

• The greenhouse gases you need to know about are:– Carbon dioxide (CO2)

– Methane (CH4)

– CFC’s (chlorofluorocarbons)

– NO4 (Nitrogen oxides which also cause acid rain.)

Global Warming

• At present the average temperature of the Earth is getting warmer and warmer.

• This is know as global warming.

• Global warming is happening because humans are putting more and more greenhouse gases into the atmosphere.

Global Warming

Where do the Gases Come From?Greenhouse Gas Human Contribution

Carbon Dioxide Burning fossil fuels in our cars and power plants.

Burning down forests for farmland.

Methane Produced by farm animals like cattle and sheep.

Produced from rotting rubbish in landfills.

CFC’s Used in refrigerators and air conditioners. Outlawed but still used in many countries.

Nox Created by burning petrol in cars.

What are the Effects?

• Higher temperatures of 2 to 5 during the next century. (A drop in that temperature caused the last ice age.)

• Melting of the polar ice caps, which could cause a rise in sea level of 10cm to 30cm. This would cause major flooding of costal areas.

• Violent weather, storms, tornados, hurricanes.• More cloud cover and rain in some areas.• Changes in sea currents which could cause a new ice age.• Less rain in some areas which could increase the size of

old deserts and create new ones. This would devastate some major crop growing areas.

• Changes in food webs and the extinction of species.

Work to Do

• Complete questions 1-8 page 63.

• Complete C5S3

• Homework– H/W sheet 5.3– Define the following keywords:

• Atmosphere, biodiversity, global warming, greenhouse effect, hurricane, ice cap, infra red, volcano

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