Module1DeepSouthPeriodOneIntroduction,ReadingandVocabulary课件外研版选修8.ppt

Polar-ice meltdown Some scientists warn that ice near the Earths Poles may indeed be melting.This “polar meltdown” may be the first sign that the Earth is heating up.We could be in very serious trouble if this trend continues.①It is estimated that a meltdown of as little as 10 percent of;Antarctica‘s ice would raise sea levels around the globe by 4 to 9 meters.Floods would cover low-lying regions and turn coastal cities like New York and New Orleans into real life underwater world. Scientists first predicted in the 1970s that heat trapped in the Earths atmosphere could cause a polar meltdown.Many people now believe that human activities are turning up the heat.When we burn fossil fuels like coal and oil，we add carbon dioxide (CO2) gas to the Earths atmosphere.Cutting down trees also makes CO2 levels rise;because trees normally soak up CO2 to make food.Scientists say higher CO2 levels strengthen the “greenhouse effect” and could increase the Earths temperature.②In fact，CO2 levels have risen by 30 percent since the Industrial Revolution of the 18th and 19th centuries. Over the past three years，satellite measurements have shown a sea level rise of about a quarter inch worldwide.③“If nothing is done to reduce fossil-fuel pollution and global warming，sea levels will rise even more.” says geologist Richard Alley. ; But even Alley admits that a polar meltdown would take time.The ice in Antarctica and Arctic locks up nearly nine times the volume of water contained in all the worlds rivers and lakes.These are such big “ice cubes” and it would probably take thousands of years to melt them. Another scientist Charles Bentley doesnt think a meltdown will happen at all.“Even if warmer temperatures begin to melt polar-ice，” he says，“the excess moisture would most likely be redeposited as snow.” In other words，the melted ice would evaporate into the atmosphere，refreeze，and fal