¹     "It is a lot warmer this year." That is being said in many parts of the world. Why? Scientists say it is because of global warming. Global warming means that our Earth is getting warmer. A warmer Earth affects how much rain falls. It causes ice caps and glaciers to melt. This makes the water in the seas and oceans higher. It affects plants, animals, and people. The things that people do make our Earth warmer. In some places, warmer weather is not bad. In other places, it is a problem.
 
²     The greenhouse effect helps keep our Earth warm. Certain gases in the air do not let heat from the sun go into space. These gases trap heat in the atmosphere. They help keep Earth warm enough for us to live. The greenhouse effect is becoming stronger. There are more of these gases in the air. Our Earth is warmer.
 
³     Scientists say that the things people do send more greenhouse gases into the air. Most scientists agree that people have caused global warming to increase. Around 250 years ago, many machines were invented. These machines made people's lives easier. They also sent gases into the air. Since then, many more machines have been invented. They still put greenhouse gases into the air. We need to use energy to run machines. We need energy to drive cars. We need energy for light and heat. The energy comes from burning coal and oil. This sends more greenhouse gases into the air.

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