About four or five million years ago, however, a new agent of change emerged in the form of hominids (ancestor of ape) culminating in the evolution of Homo sapiens or modern humans, that are considered by many to be the most powerful present generators of environmental change.
Man is no longer the product of his environment; he is also its transformer and creator. In fact, human beings have been an ecological dominant since their emergence on the earth. Man, in other words, has been interacting with his physical environment right from the primeval stage of human development and continues to do so even in this age of space technology with greater vigor.
With the advance in science and technology the frontiers of knowledge have expanded beyond the cosmic space and the environment of the earth has been transformed beyond recognition. People in their increasing numbers and technological skills have placed their imprints upon the natural landscape and environment, transforming the physical surroundings to conform to their needs.
In some instances, such as that of mega cities, conurbations and modern towns on land and seas, the human imprints may be so complete that original landscape of nature has been totally wiped away and replaced by man-made cultural environment.
The degree and magnitude of man’s impact on environment may be appreciated from the fact that just in a small fraction of geological time scale of our brief presence on earth, humans have become a powerful agent of change in the global environment.
In other words, during the last one hundred years or so, we have come equal to or perhaps exceeded the powerful natural forces that for billions of years have shaped the face of our earth and the nature of life and biosphere on it.
Consequently, there are the problems of global warming, sea level change, acidification, Stalinization, environmental pollution, ozone depletion, desertification, reduction in bio-diversity and serious ecological imbalances, endangering the very survival of mankind (Husain, 1992).
The present chapter presents a synopsis of the history of natural and cultural environment during the last about four million years. The environmental change during the Quaternary, Paleolithic, Mesolithic and Neolithic periods have been briefly presented.
Environmental changes during the historic period, especially after the Industrial Revolution (1779) when the fossil fuel was started is being used for industrial and domestic purposes and large-scale mineral extraction, have been examined.
A synoptic view of the impact of agricultural development in the developed countries and Green Revolution in the developing countries has also been made.
Human beings must always have been concerned with their environment since it was their immediate surroundings that provided the resources necessary for survival. For pre-historic and pre-literate times the only testimony to this lies in pre-historic cave paintings.
These cave paintings, depicting the pictures of aurochs, sheep, goats, horse, deer, dog and wolf, give an idea about the wildlife, erstwhile environment and man’s relationship with his surroundings.
The agents of environmental change are numerous and the processes involved in this change are very complex. During the past two or three million years, the major agents of environmental change have been climate and humans, both of which directly affect the processes operative in environmental systems (Thomson et al., 1986).
All natural systems are in a state of dynamic equilibrium. Most environmental systems, however, have both resilience and resistance to change and it may be that positive feedback occurs over such a long time Period (especially in relation to the human life span), that change is gradual and imperceptible.
For example, it is only in the last decade’ that the ravages of ‘acid rain’ on Scandinavian lakes have been recognized, although the actual process of acidification began several decades ago with increased use of fossil fuel.
It may be some considerable time before a threshold between one ecosystem and its replacement is crossed. Occasionally, some lithological changes and catastrophic changes such as volcanic eruptions may occur to create completely new landscape.
The creation of island of Surtsey, off the coast of Iceland between 1963 and 1966, and the alarming rapid demise of tropical forests in Amazonia due to human agencies are examples in which external factors have overwhelmed internal ecosystem mechanism
These are the examples of radical transformation of environment. A human agency of environmental change has only become significant in the last ten thousand years or so, but as technology has developed their impact has greatly increased.
Environmental change has occurred as humans have exploited the environment for resources. In other words, the human impact on environment is chiefly due to the need to manipulate energy.
Moreover, the continued exploitation of fossil’ fuels for industrial and domestic purposes and the development of new energy sources such as nuclear power have themselves a considerable environmental impact.
Thus, one of the major reasons of human-induced environmental change is the necessity to manipulate energy transfer.