The condition of ecological crisis is reached because of the degradation of the ecosystems. This is the outcome of the over exploitation of natural resources by man. This was inevitable in view of the population explosion, technological advancement, industrialization, profit oriented capitalism, unplanned urbanization, modern agricultural practices, deforestation, etc. the cumulative effect of all these activities of man, especially during 19^th and 20^th centuries, is the induction of undesirable changes in the environment (soil, water, air) making it less suitable for organisms. This is called environmental pollution, which ultimately is responsible for the present ecological crisis.

Some of the human activities responsible for changing environment and consequent ecological crisis are discussed here.

Man and Farming.

Agriculture involves intervention and modification of natural ecosystems. The demand of various agricultural products has been constantly increasing because of the ever-increasing human population. Therefore, man has been trying to extract more and more from the available land. This involved heavy use of synthetic chemical fertilizers, manipulation of soil conditions by tillage, control of soil moisture by irrigation and drainage, etc. On the one hand, this helped to increase the agricultural production while; on the other hand, these chemicals have caused considerable degradation of the environment over the years. For example;

1. Deforestation over the years for clearing the land for agriculture has destroyed flora and fauna of large number of ecosystems all over the world.
2. Intense cultivation without proper soil management leads to soil erosion, depletion of soil nutrients and desertification.
3. Irrigation without proper drainage leads to water logging, salination and degradation of the quality of soil.
4. Indiscriminate use of chemical fertilizers and crop protectants, especially of the non-biodegradable types, results in their accumulation in harmful concentrations in soil, water, etc. They also accumulate in bodies of organisms causing various health problems.

Industrialization:

Industries provide all the essential as well as luxurious modern amenities. Their role in improving life styles and standards of human societies cannot be denied. Industries have become indispensable component of the modern age. However, industries have adversely affected and changed the environment e.g.

1. Land for setting up industries is acquired either by deforestation or by converting agricultural land.
2. Industries consume huge quantities of raw materials and energy. This results in over exploitation of natural resources and disturbs natural cycles and balance of nature.
3. The various poisonous gases, smoke, etc. released from industries pollute soil and water. Thus, industries are growth of industries is the main cause of unplanned urbanization leading to unequal distribution of human population. In addition, greater the population, greater is the pollution of the given environment.

Thus, while industries have become an essential component of modern life, they are also the main factor of degradation of environment and ecosystems. Hence, industries may be described as the “necessary evils” of the modern age.

Technological growth. 

Technology is closely linked with or is inseparable from science. The two are complementary to each other. The scientific knowledge is used to develop a technology and then the technology used for the advancement of science and benefit of mankind.

The advancement in biotechnology during the past few decades has immensely helped in the field of cell and molecular biology, genetic engineering, medicines, medical application, etc. This has resulted in increasing longevity of life and reducing in death rate. Consequently, the global human population continued to increase at alarming rate resulting in the present population explosion. This is especially true for our own country. With the population growth, all kinds of ecological problems also came up leading towards the ecological crisis.

Pollution.

“Pollution refers to any undesirable change in the physical, chemical or biological characteristic of our environment (air, water, soil) that may or will adversely affect human or other species and life-supporting systems of our biosphere directly or indirectly.”

A substance or factor whose presence can damage the usefulness of a resource is called the pollutant.

Large quantities of various gaseous, liquid and solid waste generated by industry and other human activities act as pollutants. These are grouped into two main categories:

1. Biodegradable pollutants e.g. human and animal wastes, agro based residues and fertilizers, etc. However, these can be harmful if their input exceeds the decomposing capacity of the ecosystem.
2. Non-biodegradable pollutants e.g. heavy metals, D.D.T, pesticides, etc. These enter the food chains and they may be magnified to dangerous levels in higher tropic organisms.

The various categories of common pollutants may be listed as follows.

1. Deposited matter (e.g. soot, smoke, tan, dust, grit)
2. Gases (e.g. SO₂ , CO, CO₂, NO, H₂ S, ammonia, fluorine, chlorine, etc.)
3. Chemical compounds (e.g. aldehydes, arsines, hydrogen, fluorides, phosphogens, detergents, etc.)
4. Metals (e.g. Pb, Fe, Zn, Hg, etc.)
5. Ecological poisons (e.g. various biocides)
6. Sewage
7. Radioactive substances
8. Noise
9. Heat.

The pollution caused by these pollutants may be classified as air pollution, water pollution and soil pollution.