Climate is defined as the average weather conditions at a place over many years. Change is defined as any deviation from the norm. Over the years the earth's climate has change with an increase in average temperature constituting what is called Global Warming. Global warming is a phrase that refers to the effect on the climate of human activities, in particular the burning of fossil fuels (coal, oil and gas) and large -scale deforestation, which cause emissions to the atmosphere of large amounts of greenhouse gasses, of which the most important is carbon dioxide. Such gases absorb infrared radiation emitted by the Earth's surface and act as blankets over the surface keeping it warmer than it would otherwise be. Associated with this warming are changes of climate. (Weler, 2002)
Causes
Most scientists believe that human activity is the cause of increasing greenhouse gases, resulting from burning of fossil fuels. However, a few scientists say that recent warming could be due to natural causes.. Still other scientists claim that the evidence for warming is not convincing. Their argument is that the temperature sampling around the world is incomplete, especially in very cold areas that are inaccessible. For every iceberg that melts, new ones are forming, with the exception of satellite images showing entire ice caps (like Greenland) melting. Although, there are satellite measurements and balloon measurements, how accurate are they and how can we know for sure just what is the average temperature of the earth?
Natural Causes
Some scientist say that global warming has natural causes, they argue that we know from studying the earth's history that there have been Ice Ages and global warming periods long before humans existed. Scientists do not know precisely why these major climate changes have occurred, but there are some possibilities:
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- Solar variability ("sun spots" / cycle)
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- Volcanic eruptions on a massive scale
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- Changes in earth orbit
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- Changes in earth's orientation toward the sun
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- Effects of large meteors hitting the earth although rare
As the world evolves, changes in the earth's environment affect the climate in various ways. For example, violent nuclear reactions on the sun generate even more heat than the sun normally gives off and some of this heat makes it to the earth causing rising temperatures. Volcanic eruptions on Earth can cause temperatures to decrease, because the ashes and particles given off can prevent sunlight from passing through the atmosphere. Any slight change in the earth's orbit could cause the earth to move closer or farther away from the sun over a period of tens of thousands of years. This could radically change temperatures, because the earth would be closer or farther away from its principle source of heat. (Pidwirny, 2007) Changes in tilt or rotation known as obliquity also will effect climate zones and how heat circulates around the globe. It causes differences between summer and winter. When the tilt is less there less differences in seasons. Amount snow will increase because less melting will occur because of cooler shorter summers and longer milder winters, still with below freezing temperatures, but warmer air will produce more snow. (Tennesen, 2004, pg. 144)
Human Causes
Many scientists believe that humans have been artificially raising he concentration of greenhouse gases in the atmosphere over the past 250 years. Factories, power plants, and cars burn coal and gasoline and spit out an endless stream of carbon dioxide. We produce millions of pounds of methane by allowing our trash to decompose in landfills and by breeding large herds of methane-belching cattle. Nitrogen-based fertilizers, which we use on nearly all our crops, release unnatural amounts of nitrogen oxide into the atmosphere. They also fear that the increased concentrations of greenhouse gases over the last 100 years have prevented additional thermal radiation from leaving the Earth. (Weler,2002)
Activity:
The students will gather information on the three theories surrounding global warming: natural causes, human causes and no evidence of global warming. They will use the information to create a chart displaying facts of each theory and than create a Venn diagram to see if any information from each overlaps the other.
