The Earth's atmosphere has changed over time. During the Ice Ages, huge ice glaciers covered much of North America under hundreds of feet of ice and snow. There have also been periods of global warming when polar ice has melted, flooding many lowland areas. One cause of these changes is the amount of materials like dust, soot, ash and gases in the atmosphere. How much of these materials are in the atmosphere affects the amount of energy that the Earth can absorb from the sun, making the climate warmer or cooler.
Today about 70% of the sun's energy entering the atmosphere is absorbed by the Earth; the rest is reflected back into space. At night excess heat radiates from the Earth and the planet cools. But gases like carbon dioxide, water vapor or air pollution block this radiation process and prevent the Earth from cooling. This is called the greenhouse effect. There is strong scientific evidence that increased pollution over the past hundred years has added to the amount of greenhouse gases in the atmosphere, causing our climates to change - hotter summers, new precipitation and wind patterns, stronger cyclones. If the global warming process continues, our planet will experience serious problems.
Which of these examples most closely models the greenhouse effect?
A
Turning on several fans at once can keep you cool in a heat wave.
B
Reinforced windows keep heat inside your house in the winter.
C
Opening the door lets the air conditioning out in the summer.
D
Lighting a fire keeps the drafty ski lodge warm when it’s snowing.