GED Science Practice Test: Global Warming

As mentioned in the second ecology lesson, carbon dioxide contributes to creating a habitable warm environment through the greenhouse effect. Carbon dioxide serves as a sort of blanket for earth.  However, when there is too much carbon dioxide, too much warmth is retained on earth. This is called global warming.  While the earth’s temperature experiences natural fluctuations over the course of hundreds of years, the increase earth’s temperature over the last couple of hundred years correlates strongly with human’s increased releasing of carbon dioxide into the air. Climate scientists and ecologists differentiate between natural fluctuations in the carbon dioxide in the atmosphere, and anthropogenic, or man-made, sources of carbon dioxide.  The following graph shows the correlation between carbon dioxide production and global temperature:


The production of electricity is the largest anthropogenic source of carbon dioxide that enters our atmosphere.  Electricity produced through the burning of coal, oil, and natural gas generates a large amount of carbon dioxide.  The second largest source of anthropogenic carbon dioxide is the burning of gasoline through transportation.  The third largest source of anthropogenic carbon dioxide is through industrial processes, such as manufacturing.

Ultimately, it may not be clear why an increase in global temperature is a cause for alarm, since we experience short-term fluctuations in temperature each season without extreme adverse consequences.  In fact, you might hear people say “there is no global warming because we had more snow this winter than last winter!” Many people misunderstand the difference between weather, which reflects short-term changes in temperature, and climate, which reflects long-term changes in temperature.  While a glacier, for example, may melt a bit in the summer, it will refreeze in the winter.  These changes to a glacier reflect changes in weather.  However, if the global temperatures increase, even a few degrees and stay that way over a hundred years, the melting glacier water can cause sea-level rise. Additionally, water expands as it gets hotter.  So the existing water in the oceans will rise, simply due to the properties of water.  One of the biggest concerns of global warming is this sea-level rise, because our coastlines will be permanently changed, and a number of coastal cities, such as San Francisco, would be permanently flooded and unusable.

Another concern in global warming is the changes to ecosystems.  While humans are very adaptable and can live in cold and warm climates, many plant and animal species are adapted to only one climate and ecosystem, and cannot freely move from one ecosystem to another.  As colder biomes, such as the taiga, become warmer, perhaps changing to resemble a temperate rain forest, the organisms that lived in the taiga would be severely impacted.  Whole biomes could shift in geographic location, impacting our food supplies, existing structures for transporting food from one area of the country to another, and the ability of plants and animals to survive the change.

It may be difficult to imagine how an individual can make a difference in a seemingly distant process like electricity production, or designing cars that use alternative sources of fuel, climate scientists and ecologists think that there is a great deal that can be done on the individual level. Simple acts like turning off lights, unplugging appliances, carpooling and walking can decrease the carbon dioxide individuals contribute to the atmosphere.  Additionally, purchasing decisions like buying energy efficient bulbs, appliances, and cars can also reduce carbon dioxide emissions.  In drawing light to the numerical changes that can be made by such acts and purchases, scientists help make people aware of their carbon footprint, or the amount of carbon dioxide an individual or small group creates.  The idea is that if many individuals make these small changes, the reduction in the amount of carbon dioxide emitted into the atmosphere could be drastically decreased.  These small changes can add to, or create the demand for larger changes in infrastructure, such as the creation of cars that use alternative fuels, or power plants that use renewable resources that don’t generate as much carbon dioxide.  The following pie chart shows the breakdown of a typical carbon footprint, with pieces of the pie coded differently to reflect things we have direct control over to those we have indirect control over:



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