Introduction to Climate Change
The Earth is heated by the Sun, receiving energy in the form of sunlight. A lot of this is stored by the atmosphere and by the oceans. The Earth too, gives off heat, although this cannot be seen as light, but sometimes as heat shimmers on a hot day. This balance of incoming and outgoing heat keeps the Earth's climate fairly stable, at an average temperature of about 15°C. This is warmer than the Moon's surface because greenhouse gases in air trap more heat in the atmosphere. This is called the natural greenhouse effect.
Over time however, changes can occur in the amount of energy coming from the Sun, or in the way that heat is stored in the atmosphere and oceans. These changes can cause the Earth's climate to shift. Air pollution from volcanic eruptions can block some sunlight and cause a small cooling of the Earth's climate for up to 2 years. Changes in ocean currents and in the amount of energy given off by the Sun may also influence climate over tens or hundreds of years. Changes in the way the Earth orbits the Sun could explain the Earth's Ice Ages, the last of which ended only 14,000 years ago.
Far back in the history of the Earth, the planet was once much warmer than it is today. Over time it has gradually cooled down because of the drifting of continents and the building of mountains, which have affected the way heat is stored in the atmosphere and the oceans.
30 years ago scientist predicted that the next Ice Age was on its way. Today, we have become far more concerned about the possibility of global warming. Mankind, through pollution of the atmosphere, has increased the amount of greenhouse gases in air. This has increased the strength of the greenhouse effect, which may explain the rise in the Earth's surface temperature during the 20th century.
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• Introduction
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