The Earth's Biggest Threat 地球危機――溫室效應
by Levi King
 Global warming was once considered unlikely to be real. Recently, though, it has become widely accepted as fact. Scientists have calculated that the earth's atmosphere has gotten approximately 0.75 degrees Celsius warmer since 1900. This may not seem like much, but scientists predict an additional increase of between 1 and 7 degrees Celsius by the year 2100. This slight change could be enough to cause disasters such as extreme weather, crop failure, extinctions, melting glaciers, and rising sea levels.
It's possible that natural phenomena like volcanoes, solar flares, and shifts in the earth's orbit could be causes of this change. However, scientists now believe that changes in the atmosphere are primarily to blame for the rise in temperatures. Light from the sun enters the earth's atmosphere and warms the air, land, and oceans. As heat radiates back through the atmosphere toward space, some of it is trapped by gases and continues to warm the earth. This is called the greenhouse effect, and the gases that trap the heat are greenhouse gases.
Without the greenhouse effect, life couldn't exist on earth. However, rising levels of greenhouse gases are trapping more and more of the sun's heat. As people burn fossil fuels or clear forests, carbon dioxide, a greenhouse gas, is released into the atmosphere. As the oceans warm, water vapor, which is also a greenhouse gas, enters the atmosphere. This combination of pollutants and water vapor creates the powerful and dangerous cycle behind global warming. It is a cycle that, if active measures are not taken, could have serious and deadly consequences for all living things in the near future. |
