Happy Earth Day! As citizens of Planet Earth, it's important for us to take some time each year to think about and celebrate this third rock from the Sun we call home.

As you learn about recycling and being “green," you'll probably hear the phrase “carbon footprint." These footprints aren't easy to see, though!

Your carbon footprint is a measure of the amount of greenhouse gases your human activities produce, either directly or indirectly. It's usually expressed in a number of tons of carbon dioxide.

Greenhouse gases, such as carbon dioxide, ozone, and methane, are those gases that scientists believe are contributing to the depletion of Earth's ozone layer and thus leading to climate change. The more of these gases your activities produce, the more damage you could be doing to the environment.

For example, when you ride in a car to soccer practice, the car's engine burns fuel. That process produces a certain amount of carbon dioxide that is released into the atmosphere. Other types of activities that produce carbon dioxide include heating your home and any activities that rely on electricity, since the generation of electrical power usually involves greenhouse gas emissions.

Some carbon footprint emissions are considered to be from direct sources. The fuel you burn in your car, for example, is a direct source.

Most sources of emissions, though, come from indirect sources. For example, when you buy a product that was produced far away from you, the fuel burned to produce and ship that product to you is considered an indirect source.

As you can probably see, measuring your carbon footprint can be a difficult task. In fact, it's probably impossible to measure it exactly, given the large number of indirect sources involved. However, scientists have come up with many different ways of calculating your carbon footprint that will give you a rough estimate of the amount of greenhouse gases your activities produce.

You might be surprised to learn just how much of an impact your activities produce. Global climate change is a worldwide problem, but each and every one of us contributes to it through our own decisions and actions. Measuring your carbon footprint is one way of gauging how much of an impact your activities have.

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