The Earth's climate is changing, and people's activities are the main cause.
Our world is always changing. Look out your window long enough, and you might see the weather change. Look even longer, and you will see the seasons change. The Earth's climate is changing, too, but in ways that you can't easily see.
The Earth is getting warmer because people are adding heat-trapping gases to the atmosphere, mainly by burning fossil fuels. These gases are called greenhouse gases. Warmer temperatures are causing other changes around the world, such as melting glaciers and stronger storms. These changes are happening because the Earth's air, water, and land are all linked to the climate. The Earth's climate has changed before, but this time is different. People are causing these changes, which are bigger and happening faster than any climate changes that modern society has ever seen before.