Depletion of Ozone Layer
The stratosphere has a layer of ozone that protects us from the harmful ultraviolet (UV) rays of the sun. Exposure to these rays cause skin cancer and cataracts. However, the ozone layer filters out the dangerous UV rays from sunlight as it enters the earth's atmosphere. The cholofluorocarbons (CFCs) that are man-made chemicals are released in the atmosphere through CFC containing aerosols, refrigeration equipment, foam and as by products of certain industrial processes. As these chemicals are released, they rise into the atmosphere and break down the ozone molecules that form the ozone layer. There is an ozone hole in the Antarctic stratosphere that is causing great concern to environmentalists all over the world. Because of the ozone holes in the upper atmosphere, the Earth receives excessive ultraviolet radiation from the sun. This is harmful for trees and plants (and for animals and human beings who depend on plants). The UV rays can destroy a certain type of bacteria known as Cyanobacteria that are important for a number of economically important crops. Researchers are even predicting that excess level of UV rays could lead to the death of the phytoplanktons, that are an important component of the food web of the oceans.
Pollution
Industrialization has been the hallmark of human progress. However, with industries have come a host of toxic gases that are being released into the atmosphere even as I write this article and you read it. Industries release gallons of liquid waste into the seas and rivers. Some of the effluents percolate down and reach the ground water and pollute it to the extent that it can't be used by human beings for drinking or cooking. Intensive agriculture and excessive use of fertilizers and pesticides are destroying the natural land and driving animals away. Besides adding to air pollution, the innumerable vehicles running on the roads add to noise pollution that has led to an increase in stress, anxiety and problems related to hearing. Water pollution has led to a decrease in the number of various aquatic animals. Several aquatic life forms are on the verge of extinction. Migratory birds are known to change their course due to pollution or change in weather. Respiratory diseases in human beings is another price that we are paying for polluting the environment. Acid rains can kill trees, destroy crops and fish life in lakes and streams. Ingestion or inhalation of toxic substances increases the chances of having life-threatening diseases like cancer.
Deforestation
Increasing population, industrialization and need of land for development of expanding cities has led man to cut down forests selfishly. Not only are the forests home to a large number of animals, trees are also an important component of the water cycle. The roots of plants hold the soil together and prevent soil erosion. The global forest cover has shrunk to half its area in the last 11,000 years. During the period between 1990 and 2000 itself, the yearly loss of natural forests was 16 million hectares. Deforestation at such alarming rate has been a cause of constant worry for environmentalists the world over. 'Biodiversity' plays an extremely important role when it comes to maintaining the life on Earth.
Extinction of Species
The variety and interdependence of all living things has led to the evolution of world. Man has been killing animals right since the time he acquired the skill of hunting. Although in those times, hunting was the means for survival, human beings continued to kill animals even after they had learned to cultivate crops. The relentless hunting by human beings, sometimes for the hide of a cheetah or the tusks of the elephants, or simply to cook the tasty shark fin soup, has wiped out the existence of a large number of animals in just a century. Besides hunting, human activities like environmental pollution and deforestation has led to the extinction of a large number of animals and plants due to loss of habitat. Recent studies have shown that in North America, 37 animal species have become extinct in the last 50 years due to human activities. Loss of habitat led to the extinction of the Bali subspecies of tiger in 1937. According to the 2008 annual IUCN (International Union for Conservation of Nature) report, there were 16,928 animal and plant species that are threatened of extinction and the list keeps increasing every year.
Read more at Buzzle: http://www.buzzle.com/articles/how-do-humans-affect-the-environment.html