The Earth's climate has changed many times in the past.
Subtropical forests have spread from the south into more
temperate (or milder, cooler climates) areas. Millions of years
later, ice sheets spread from the north covering much of the
northern United States, Europe and Asia with great glaciers.
Today, nearly all scientists believe human beings are changing
the climate. How can that be? Over the past few centuries,
people have been burning more amounts of fuels such as wood,
coal, oil, natural gas and gasoline. The gases formed by the
burning, such as carbon dioxide, are building up in the
atmosphere. They act like greenhouse glass. The result, experts
believe, is that the Earth heating up and undergoing global
warming. How can you show the greenhouse effect? What do you
need? - Two identical glass jars - 4 cups cold water - 10 ice
cubes - One clear plastic bag What to do? - Take two identical
glass jars each containing 2 cups of cold water. - Add 5 ice
cubes to each jar. - Wrap one in a plastic bag (this i