The sun is getting hotter . It is also very old . It is about 4,500 million years old ! The Earth's climate has been changing for all those years . But the climate is heating up much faster now . Humans and their machines are responsible for the rapid heating up of the Earth . Almost all machines use fuels such as oil , gas or coal . All of them are polluting environment . Much of this pollution contains a gas called carbon dioxide . It is this gas which pollutes the atmosphere .