Deserts do not stay the same size  .Sometimes they grow bigger. Sometimes they get smaller. The world's biggest desert, Sahara, is in Africa. Right now, the Sahara desert is growing fast. Why is the Sahara growing ? In some places , People farm too much.  In other places ,animals eat all the grass. or people cut down the trees. This makes the soil  weak. Weak soil lets the desert grow. Why is it a problem? people can not grow food in the desert. people can not build houses, hospitals , or schools in the desert . so people must leave their homes .They must live somewhere else. What can people do ? They can plant trees. They can also farm less. These things make soil stronger. maybe the Sahara will stop growing . It's a big problem. Many people must work together to solve   it? What do we know about deserts ?
Their size never changes They are caused by people They can make trouble for people They are all in Africa.