In geographical literature, the ways in which human beings have changed and are changing the face of the earth and the human role in the natural processes and systems have drawn the attention not only of natural scientists but also of social scientists as well as of planners and policy makers.
(A) Human Impact on Climate and Atmosphere:
The increasing human population and the rising level of technology both have become significant factors in the variation in world climate and are responsible for the various changes in atmospheric conditions as well as of air pollution.
The human influence on global climate is due to the Gas Emissions, (CO2 Industrial and Agricultural), Chlorofluro Carbons (CFCs) and Nitrous Oxide, Krypton 85, Water Vapour, Deforestation, Overgrazing and extension of irrigation.
(B) CO2 Emission:
The problem of CO2 emission has become a major environmental concern. Since the beginning of the Industrial Revolution humans have been taking stored carbon out of the earth in the form of coal, petroleum and natural gas, and burning it to make CO2, heat, water vapour and small amounts of SO2 and other gases, which are responsible for air pollution, green house effect, increase in surface temperature, or in other words, global warming. By 2050, it is possible that the increase in global surface temperature ranges between 1.4 and 2.2 degree Celsius.
The impact of human influence on the atmosphere is more because the atmosphere acts as a major channel for the transfer of pollutants from one place to another. It is in this way that harmful substances have been transferred long distance from their sources of emission.
A second example of the possible widespread and ramifying ecological consequences of atmospheric pollution is provided by acid rain. In recent years, the greatest attention has been focused on the role of CFCs, the production of which has been rising in last few decades. These gases may diffuse upwards into the stratosphere where solar radiation causes them to become disassociated to yield chlorine atoms which react with and destroy the ozone present there.
(C) Human Impact on Vegetation:
The human impact on vegetation is greater than on any of the other components of the environment. The nature of whole landscape has been transformed by human-induced vegetation. Man has used fire for the clearance of forest cover, mainly for the use of land for cultivation or for habitation. This practice was common during the early stage of the development of civilizations. But, this practice is still prevalent among many tribals.
Uncontrolled and heavy grazing is not only a cause of the disappearance of vegetation cover but is also responsible for desertifications and other environmental problems. The deliberate removal of forest or deforestation is one of the most long-standing and significant ways in which humans have modified the environment, whether achieved by fire or cutting.
Sometimes forests have been cut down to allow agriculture, at other times to provide fuel for domestic purposes or to provide charcoal or wood for construction etc. The spread of desert like conditions, the arid and semi-arid area is always due to man’s influence.
Some of the airs pollutants, humans have released into the atmosphere, have had detrimental impact on plants. Sulphur dioxide, for example, is toxic to them. Local concentration of Industrial fumes also kills vegetation. Photo-chemical smog is also known to have adverse effect on plants both within cities and also on their outskirts.
(D) Human Impact on Soil:
Soil is the most vulnerable of human resource and is one on which humans have had a very major impact, because they lie close to and depend an the soil. Impact on soil can occur with great rapidity in response to land use change by new technologies. Salinity is a natural characteristicis in semi-arid and arid soils. But humans have increased the extent and degree of salinity in different ways.
The extension of irrigation and different techniques used for water abstraction can lead to a build-up of salt levels in the soil through the mechanism of raising ground water level.
Construction of large dams and barrage to control water flow and to give a head of water creates large reservoir from which further evaporation can take place. The seepage of water is responsible for upward movement of ground water. In coastal areas, salinity problems are created by sea-water incursion brought by over pumping. Human activities are also responsible for the structural changes in the soil.
There are many ways in which humans can alter this, especially by compacting it with agricultural machinery and by changing its chemical character through irrigation. Grazing is another activity that can damage soil structure through trampling and compaction.
The introduction of chemical fertilizers has also changed the chemistry of soils. Sometimes these create environmental problems such as water pollution, while their substitution for more traditional fertilizers may accelerates structure deterioration and social erosion.
(E) Human Impact on the Waters:
Water is the source of life and right from the origin, human beings are using it for various purposes. The ancient civilizations have developed in river valley. This is also true about medieval townships and other developments, and all modern developments are related directly or indirectly to water. The main concern is that by using waters, humans have influenced both its quantity and quality.
Earlier, the influence of human activity on water resources was limited but now this has become a major problem of environmental degradation throughout the world. The consideration of dams and reservoirs is widespread throughout the world for irrigation purpose, to generate power or to provide a reliable source of water. The impact of human activities is especially marked in Africa and North America where about 20% of total run-off is now controlled.
The impact of dam- construction is apparent in the form of change in ecosystem and environmental conditions. The recent environment controversy over Tehri and Sardar Sarovar dams show people’s awareness against construction of dams and their possible damaging environmental impact.
The environmental consequences of dams include subsidence, earthquake triggering, transmission and expansion in the range of organism, the build-up of soil salinity, changes in ground water levels, water logging deforestation, etc.
The process of urbanization has a considerable impact, both in terms of controlling rates of erosion, the delivery of pollutants to rivers and in terms of influencing the nature of run-off and other by hydrological characteristics.
Deforestation gives rises to floods, annual run-off levels and also affects on-stream flow. In many parts of the world, humans obtain water supplies by pumping from ground water; it reduces level of water table and the replacement of coastal areas’ fresh water by salt water.