palimmn_lessonplan.doc

The greenhouse effect is a natural occurring process

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The greenhouse effect is a natural occurring process that contributes to control the Earth’s temperature. When the sun’s heat reaches the Earth’s atmosphere, some of the heat escapes back to space. The other part is absorbed and re-emitted by the Earth, then trapped in the atmosphere by greenhouse gases (such as water vapor, carbon dioxide , nitrous oxide , and methane ) , causing the Earth to heat up. Without the greenhouse gases, the Earth would be much colder (approximately 60°F colder) and could not support life as we know it. But since the Industrial Revolution, human activities have exacerbated the natural greenhouse effect by adding greenhouse gases to the atmosphere (mostly from burning fossil fuel for powering plants, transports, houses etc). If the greenhouse effect becomes stronger, more of the sun’s heat gets trapped and it makes the Earth warmer than usual. Even a little extra warming may cause problems for humans, plants, and animals. Climate changes are occurring in certain parts of the world much faster than predicted. Students name impacts of climate change in their country and in the world. 2
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Earth has warmed by about 1F over the last 100 years. Scientists expect the average global temperature to increase an additional 2 to 7ºF over the next one hundred years. At the peak of the last ice age (18,000 years ago), the temperature was only 7ºF colder than today, and glaciers covered much of North America! Even a small increase in temperature over a long time can change the climate. Climate varies naturally over both short and long time scales. What scientists think is that human activities come in addition to natural variability and thus modify the trend of the climate. The impacts of human activities on climate can be direct or indirect . For instance, there are natural sources of greenhouses gases. Such as wetlands and lakes, which emit methane , produced by the decomposition of organic matter (dead plants and animal). But the increase of the mean temperatures (due to the increased greenhouse effect) can cause a higher release of that natural gas. This is what happens in Northern latitudes. The permafrost (permanently frozen ground) is thawing. This is the same process that happens to food and ice cubes when you take them out of the freezer. When ice in the ground melts, the ground surface collapses as sink holes. These holes fill with water, forming ponds and lakes. The dead plant and animal remains (organic matter) that were previously frozen thaws out in the bottoms of lakes. It is like opening the freezer door. Microbes and bacteria eat and digest the organic matter. And as they do so, they create methane . Some people’s digestive system does the same thing with the food they eat. Northern lakes emit a lot of methane.
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