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Unformatted text preview: Jon Ahlquist 12/10/2006 MET1010 Intro to the Atmosphere 1 Chapter 16: Climate Change The Earth’s 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 Earth’s 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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- Fall '08