What Causes Global Warming?

On earth we get energy from the sun's light. As you know, it gets hot outside if the sun is shining brightly on a summer day. The reason it warms up is because the earth is absorbing some of that solar energy.

However, not all of the energy is absorbed. Some energy is reflected back into space in the form of light. This reflection allows the earth to be seen as a star from other parts of our solar system, just like we can see the moon and other planets. Energy also leaves the earth in other forms like heat, for example, which is called infrared light.

In order for our earth to stay the same temperature from year to year, the energy arriving at the earth (solar radiation) must be the same as the energy leaving the earth (infrared radiation). If we have more energy leaving than arriving, the earth will cool down and we could have another ice age. If we have more energy arriving than leaving, we will have global warming.

The reason the earth could retain more energy than it gives off has to do with the air around us and what it is made of. When we burn wood, coal, or gasoline in our cars, carbon dioxide, is released. Carbon dioxide is a gas that can't be seen or smelled, but it does trap some of the infrared energy emitted from the earth and prevents that energy from going back out into space. If the amount of carbon dioxide in the air goes up, the earth will heat up, which is the start of global warming.

Because carbon dioxide absorbs energy emitted from the earth and prevents it from going back out into space, it is called a greenhouse gas. There are several other greenhouse gases. Altogether, these other gases absorb about as much infrared energy as carbon dioxide does. So, carbon dioxide is responsible for about half of our global warming and all the other gases combined are responsible for the other half.

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