LIWA

Greenhouse Effect and Global Warming

ICSE Class 7 · Geography · Chapter 4

What this chapter covers

Key definitions

The greenhouse effect is the natural warming of the Earth's surface and lower atmosphere caused by certain gases in the air that let sunlight in but trap part of the heat given off by the Earth.

Greenhouse gases are the gases in the atmosphere that absorb heat given off by the Earth and so help to keep the planet warm.

Water vapour is water in the form of an invisible gas, and it is the most plentiful greenhouse gas in the atmosphere.

Carbon dioxide is a colourless gas given out when living things breathe and when anything containing carbon, such as wood, coal or petrol, is burnt.

Methane is a greenhouse gas given off when plant and animal matter rots without much air.

Nitrous oxide is a greenhouse gas given off naturally by tiny living things called bacteria in the soil and in the oceans.

Global warming is the slow rise in the average temperature of the Earth's surface and lower atmosphere, caused mainly by the extra greenhouse gases that human activities add to the air.

Deforestation is the large-scale cutting or clearing of forests to use the land for farming, mining, roads, dams or buildings.

Fossil fuels are fuels such as coal, petroleum and natural gas, formed over millions of years from the buried remains of ancient plants and animals.

Ozone is a form of oxygen gas whose particles are each made of three oxygen atoms instead of two.

The ozone layer is the part of the stratosphere, roughly 15 to 35 km above the Earth, where ozone is found in larger amounts and where it absorbs most of the Sun's harmful ultraviolet rays.

Ozone depletion is the thinning of the ozone layer in the stratosphere caused by certain man-made gases that break ozone apart.

Key points

Questions answered

What is a greenhouse, and why is the air inside it warmer than the air outside on a sunny day?
A greenhouse is a glass or clear plastic house for growing plants. Sunlight passes in through the glass and warms the soil and plants; the heat they give off cannot escape easily through the glass, so the inside stays warmer.
Define the greenhouse effect.
The greenhouse effect is the natural warming of the Earth's surface and lower atmosphere caused by gases in the air that let sunlight in but trap part of the heat given off by the Earth.
Name four greenhouse gases and give one source of each.
Water vapour (evaporation from the oceans), carbon dioxide (burning coal or petrol), methane (rice fields or cattle), nitrous oxide (soil bacteria, or chemical fertilisers on farmland).
Why is the greenhouse effect necessary for life on Earth?
Without it, the Earth's average surface temperature would be about -18 °C instead of about 15 °C. Water would freeze and most living things could not survive.
How is global warming different from the greenhouse effect?
The greenhouse effect is natural and keeps the Earth comfortably warm. Global warming is the extra rise in the Earth's average temperature caused by human activities adding more greenhouse gases to the air.
Explain how deforestation adds to global warming in two ways.
Trees take in carbon dioxide, so cutting them leaves more of it in the air. If the cut trees are burnt or left to rot, the carbon stored in them is released as carbon dioxide.
What are fossil fuels, and why does burning them cause global warming?
Fossil fuels are coal, petroleum and natural gas, formed from the remains of ancient plants and animals. Burning them releases carbon dioxide, a greenhouse gas, into the air.
What is the ozone layer, and what harm do CFCs do to it?
The ozone layer is the ozone-rich part of the stratosphere that absorbs most of the Sun's ultraviolet rays. CFCs rise into the stratosphere, where sunlight frees chlorine from them, and the chlorine destroys ozone particles, thinning the layer.