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23 - 1997 since 1880 The global mean temperature has...

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1 Lecture 23: Evidence of climate change Outline: Climate Change 1. Mechanism: Greenhouse effect 2. Evidence – what we’ve seen so far, and what has likely caused it. Suggested reading: Appenzeller, T. 2004. The case of the missing carbon. Nat. Geographic, Feb 2004 issue. “Radiation” The "Greenhouse Effect" Yellow = shortwave Red = longwave / IR Greenhouse effect • Natural increase in air temperatures caused by sunlight energy trapped by the atmosphere. Without greenhouse effect, surface temperatures would be ~33 o C lower (59 o F). Heat-trapping gases CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 N 2 O CH 4 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 N 2 O CH 4 …like a blanket over Earth
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2 Evidence That Climate Is Changing 1. Air temperatures are increasing. HOTTEST YEARS "EVER"* 1998 (= 2010 ?) 2008 1988 2009 1990 1994 2005 1995 1983 2002 = 2003 1999 1996 2004 2000 1944 2006 1991 1989 2001 1987 1993
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Unformatted text preview: 1997 * since 1880 The global mean temperature has increased ~1.5º F (0.8º C) over the past 150 years Earth is hotter now than it has been in at least 400 years, and probably >1000 Chapman & Davis 2010 Change in average temperatures since 1951-1980 NASA 2010 3 More evidence • 2. Melting ice packs in Arctic & Antarctica, more icebergs • 3. Rising sea levels - Causes: “thermal expansion,” melting ice • 4. Melting glaciers What could be causing warming? • Several candidate factors • By far the most consistent explanation with data: More greenhouse gases in atmosphere Carbon dioxide in the atmosphere IPCC 2007 4 Methane (CH 4 ) Carbon dioxide (CO 2 ) Where do heat-trapping gases come from? Nitrous oxide (N 2 O) Feedbacks: a little warming can go a long way… What's changing the climate? IPCC 2007...
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