A The earth can sustain life because the planet’s atmosphere works like a well ventilated greenhouse. In fact, the average temperature on the planet is 60 degrees Fahrenheit (16 degrees Celsius). The problem is that the ventilation system that keeps the planet at the right temperature is getting clogged. Carbon dioxide (CO2) produced by industry, agriculture and transportation are trapping more and more of the sun’s heat inside the atmosphere. Like a closed-up greenhouse or a locked-up car, the harmful gases on the earth’s lower atmosphere act in the same way. This has resulted in a slow but steady rise in global temperatures, which some scientists predict will cause the global average temperature to rise as much as 9 degrees Fahrenheit (5 degrees Celsius) before the year 2100.
B If the carbon dioxide cover around the earth continues to build up, the earth could someday be similar to the planet Venus. Venus is a planet (otherwise very similar to ours) that has a highly advanced greenhouse effect. It has a thick carbon dioxide atmospheric cover that traps the sun’s heat and makes the surface of Venus hot enough to melt lead. But the earth is a long way from that kind of scenario right now.
C Since the 1980s global temperatures have been rising at what many scientists feel are alarming rates. If temperatures continue to rise, scientists predict several types of environmental disturbances. The most commonly known theory of global warming is the greenhouse effect.
D Still, the planet faces risks from rising global temperatures that could be catastrophic. Droughts, more frequent tropical storms and extinction of some species could result from global warming. This would seriously disrupt our planet’s food production. And hotter weather in the northern and southern arctic regions could result in the melting of polar ice caps, which would cause coastal flooding in ocean bordering countries.
E Some scientists are hopeful that nature itself will help reduce the greenhouse effect. One way nature could accomplish this would be by increased cloud cover. More clouds would absorb more heat and therefore lower temperatures. Another thing in nature that could help is plankton, which is a living organism found in oceans. Plankton naturally absorbs carbon dioxide, thus reducing the greenhouse effect.
FGreenhouses are made of glass; this lets in the sunlight all the time. The sunlight warms up all the plants and equipment in the greenhouse. The plants and other objects then give off heat but the glass walls of the greenhouse do not let the heat escape -- it stays inside. Without proper ventilation the temperature in the greenhouse would rise to unbearable heights and kill all the plants. Another example of this effect is when a car is parked in the sunlight with all its windows rolled up.
G In 1990 a group of 170 scientists from around the world released a report warning that the greenhouse effect would continue to increase noticeably unless something was done. In 1992, over 150 nations signed a declaration outlining the need to reduce global warming. In reaction to this, many nations have recently passed new, more restrictive pollution laws.
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