The Earth is always changing because of volcanoes, earthquakes and, of course, wind and rain. Some of these changes are very slow and others are quick. Water and ice can make very big changes to the planet. For example, glaciers (rivers of ice) can cut through mountains and make deep valleys. 

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It's normal for our planet to change. But at the moment scientists think it's changing faster than usual. They don't understand everything that is happening but they know that temperatures are rising. The weather is getting better in some places and drier in others, and there are more big storms. They say that the recent increase in extreme weather events: more frequent and powerful hurricanes, more frequent and intense floods and droughts, is an indication that climate change has already started.