The 20th century, especially in the second half, has been one of rapid change in the Earth's environment. The impact of humans on the physical form and functioning of the Earth have reached levels that are global in character, and have done so at an increasingly mounting speed. 20 years ago the environment was seen as posing a threat to the future of humanity as death rates from natural hazards had increased dramatically since the turn of the century. The Earth though has always been plagued by natural disasters. Now, with the world populatio ....