Scientists believe that the earth's climate may be warming up. This trend probably began thousands of years ago.Many areas of the earth used to be covered with ice that has now melted.However, in recent years,the warming trend has speed up.Scientists think that part of the reason for this may be carbon dioxide pollution from industry and automobiles. The carbon dioxide mixes with other gases.This pollution covers the earth like a blanket and keeps it warmer. Another reason for the warming may be the fact that the earth is losing its forests.Forests are an important past of the earth's system for using up carbon dioxide and keeping the air temperature cool.