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1、Climate Change,What is Climate Change？,Climate is the average weather at a given point and time of year,over a long period(typically 30 years).Although we expect the weather to change a lot from day to day,we still expect the climate to remain relatively constant.Once the climate doesnt remain const
2、ant,we will call it climate change.,Observations of climate change,what can you see from the chart?,Global mean temperatures are rising faster with timeWarmest 12 years:1998,2005,2003,2002,2004,2006,2001,1997,1995,1999,1990,2000,Observed surface temperature trend,Trends significant at the 5%level in
3、dicated with a+.Grey:insufficient data,Other evidence of Climate Change,1875,2004,Area of seasonally frozen ground in NH has decreasedby 7%from 1901 to 2002,Increased Glacier retreat since the early 1990s,Arctic sea ice area decreased by 2.7%per decade(Summer:-7.4%/decade),Spring snow covershows 5%s
4、tepwise drop during 1980s,Spring snow covershows 5%stepwise drop during 1980s,Some aspects of climate have not been observed to change:TornadoesDust-stormsHailLightningAntarctic sea ice,Direct Observations of Recent Climate Change,Global surface temperatures have risen by about 0.6C since 1900It is
5、likely that this warming is larger than for any century since 200AD,and that the 1990s were the warmest decade in the last millennium.The warming differs in different parts of the world,but over the last 25 years,almost everywhere has warmed,and very few places have cooled.Other changes have occurred,e.g.:Sea level has risen by about 20 cm,Ocean heat content has increased,Almost all mountain glaciers have retreated,Summary,
