公共英语网络辅导班

Most scientists believe that the rapid expansion of agriculture and industrial activities over the last several hundred years have generated significant increases in carbon dioxide and methane in the atmosphere. However, experts disagree about whether such changers have caused the increase of approximately 0.5℃ in the earth’s surface temperature that has been documented over the past century. Many scientists cite the fact that 1997 was the warmest year on record, following a decade in which 9 of the 11 hottest years of this century were reported, as strong, but circumstantial, evidence that human activities have altered the earth’s climate. Other experts, however, believe this temperature trend is a natural variation.