The impact of man



There is no doubt that mankind is now altering the Earth significantly and that no part of the global system is immune. The envelope of air surrounding the globe, the oceans—which cover about 70% of the surface—the land surface, the subsurface, and the biosphere all feel the impact of man. Also, it is true that however brief the period of time that human beings have lived on Earth, and long before the present, they have altered the land and water in important ways. All energy used by mankind, the number of people on Earth, and the combination of the two, which stresses the global system far beyond anything experienced heretofore makes the 20th century different than previous times.