Unit4 Globalwarming
step 7 homework1.learn the useful new words and expressions in this part by heart.2.try to find some data about global warming on the internet，and show your class in the next period and talk about them.step 8 reflection after teaching________________________________________________________________________________________________________________________________________________教學參考about global warming(關于全球變暖)global warming is the increase in the average temperature of earth's near－surface air and oceans since the mid－20th century and its projected continuation.global surface temperature increased 0.74±0.18℃(1.33±0.32)between the start and the end of the 20th century.the intergovernmental panel on climate change(ipcc)concludes that mo st of the observed temperature increase since the middle of the 20th century was very likely caused by increasing concentrations of greenhouse gases resulting from human activity such as fossil fuel burning and deforestation.the ipcc also concludes that variations in natural phenomena such as solar radiation and volcanic eruptions had a small cooling effect after 1950.these basic conclusions have been endorsed by more than 40 scientific societies and academies of science，including all of the national academies of science of the major industrialized countries.climate model projections summarized in the latest ipcc report indicate that the global surface temperature is likely to rise a further 1.1 to 6.4℃(2.0 to 11.5)during the 21st century.the uncertainty in this estimate arises from the use of models with differing sensitivity to greenhouse gas concentrations and the use of differing estimates of future greenhouse gas emissions.most studies focus on the period up to the year 2100.however，warming is expected to continue beyond 2100 even if emissions stop，because of the large heat capacity of the o ceans and the long lifetime of carbon dioxide in the atmosphere.
an increase in global temperature will cause sea levels to rise and will change the amount and pattern of precipitation，probably including expansion of subtropical deserts.warming is expected to be strongest in the arctic and would be associated with continuing retreat of glaciers，permafrost and sea ice.other likely effects include changes in the frequency and intensity of extreme weather events，species extinctions，and changes in agricultural yields.warming and related changes will vary from region to region around the globe，though the nature of these regional variations is uncertain.