| Greenhouses
are used to provide warm places for fruit, vegetables
and flowers to grow when it’s too cold for them
to grow outside. Greenhouses are covered in glass or
plastic which allows light energy from the sun to come
in. A lot of the light energy is absorbed by plants
and soil and changed into heat energy. Much of the heat
is trapped inside which increases the temperature inside
the glasshouse, allowing plants to grow.
However, human activities are changing the greenhouse
effect. Using coal-fired power plants releases large
amounts of carbon dioxide into the atmosphere. Driving
cars that run on petrol also puts more carbon dioxide
into the air. Keeping large numbers of livestock, such
as cattle, can also be harmful because they release
lots of extra methane gas into the atmosphere.
All these extra greenhouse gases result in more heat
being trapped around the earth. We call this process
the enhanced greenhouse effect. When this process causes
a long-term rise in the average temperature of the earth
we call it global warming.
The earth could be thought of as being like a very large
greenhouse. But instead of glass or plastic to keep
the heat in, we have gases like water vapour, carbon
dioxide and methane in the atmosphere. The sun shines
through these gases and gives us light and warmth. These
greenhouse gases stop some of the heat from escaping
back out into space, making it warm enough for plants,
animals and humans to live on earth. Without the greenhouse
gases to trap some of the heat on earth, the average
surface temperature of the earth would be below 0 degrees
Celsius. |
