Global warming
Global warming is the rise in temperature of the air and oceans globally. It is happening mainly because humans burn coal, oil, and natural gas; and cut down forests. Average temperatures today are about  higher than before people started burning a lot of coal around 1750. In some parts of the world it is less, and in some, more. Most climate scientists say that by the year 2100, temperatures will be  to   higher than they were before 1750.