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LITE19_-_study_guide - Study Guide Chapter 19 Climate...

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Study Guide – Chapter 19 – Climate Change and Ozone Depletion The Earth has undergone many glacial and interglacial periods over the last 900,000 years, and for the last 10,000, things have been pretty calm and productive, both for humans and the world’s ecosystems. As you can see in Figure 19-2, however, the most recent part of the last 1,000 years has seen significant warming; note in the figure that the planet has been as warm as it is now many times, but this much warming over such a short time period seems to be something new. We can construct these temperature histories from radioisotopes in rocks, fossils, and ocean sediments, bubbles of air trapped in ice, pollen from plants deposited long ago, tree rings, insects and minerals in 1000-year old bat dung; in short, there are many methods to investigate the temperature history of the planet, and almost all of these are telling the same story. We talked in class about the greenhouse effect , and the primary greenhouse gasses CO 2 , methane, and nitrous oxide (along with water vapor). Note the concentration of CO 2 in the atmosphere in Figure 19-3, and the concerns by atmospheric scientists that we need to make sure that CO 2 levels remain below 450 ppm, a tipping point (think threshold effect) that could cause unavoidable changes in climate for hundreds to thousands of years. Is it worth the risk to ignore these warnings, and the models they are based on ? Although methane emissions seem to have leveled off since 1990, they are expected to rise again as increasing global temperatures melt the permafrost, glaciers, and ice caps, which releases more trapped methane, which increases the temperature, which melts the ice and releases more trapped methane, and on and on (think positive feedback). Note also that a molecule of nitrous oxide (increasing with development of modern agriculture and nitrogen-based inorganic fertilizers) is 3-10 times worse than CO 2 in terms of trapping hear, and methane is 22 times as worse! We looked at some of the findings of the report prepared by the Intergovernmental Panel on Climate Change (IPCC) in 2007. Although many industries refuse to admit the anthropogenic contributions to the current warming trend, the book talks about several lines of evidence that support the IPCC conclusions, e.g., rising temperatures, increasing CO 2 concentrations, rising arctic temperatures, shrinking glaciers and sea ice, and increasing sea level. Again, some of these factors can amplify (positive feedback) or dampen changes in global warming or cooling. Unfortunately, most of them are amplifiers. The Science Focus on pages 502 and 503 shows projected heating by 2100, note that the scale is fairly small (about +1.8 to +4.2 degrees Celcius in Figure 19-B), but the effects of these small changes in temperature could be catastrophic, or at least planet-altering.
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