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Unformatted text preview: Jon Ahlquist 12/10/2006 MET1010 Intro to the Atmosphere 1 Chapter 16: Climate Change The Earths Changing Climate Possible Causes of Climate Change Global Warming The Recent Warming Future Warming Climate and averaging Climate: average weather National Weather Service climatological normals: average over most recent 3 decades; currently 1971-2000. See http://lwf.ncdc.noaa.gov/oa/climate/normals/usnormals.html Averaging period is arbitrary, though. For various studies, averaging period can be as short as a few weeks or as long as hundreds of years No matter what the averaging period, climate is always changing with time. Scales of Changing Climate Not only does climate change on all time scales. Climate changes can be due to very local effects such as street light in fig. 16.1 and urbanization in general, to continental scale (continental drift), and planetary (orbital fluctuations). More on each of these later. Fig. 16.1, p. 432 Determining past climate Recent climate: direct measurements (over 100 years for major cities in US, nearly 200 years for Europe). For historical era: written reports of freeze dates, floods, etc. Chinese records go back several thousand years. Supplemented by: tree rings, identification of plants from seeds and pollen found in various layers Oxygen isotope ratios in coral, etc. Geological record (dry lake beds, fossils, etc.) Climate simulation programs can check consistency of observations and estimate climate in places where observations are sparse. Ice Ages (pp. 432-433, 435) Ice age: glaciers cover significant area of Earth. We are currently in a minor ice age, with glaciers covering about 10% of Earths surface. If all glaciers were to melt, sea level would rise by about 200 feet. Warming a few degrees C: sea levels up by ~1/2 m Sea level rising in some places (ice melting) and dropping in others (land rebounding from weight of past ice now gone that compressed it) Most recent major ice age: ~18,000 years ago, when sea level may have been ~400 feet lower, opening Bering land bridge between Asia and North America Precise no. of earlier ice ages is hard to say. Advance of new glaciers erases evidence of earlier glaciers.of new glaciers erases evidence of earlier glaciers....
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