From beginning of human evolution man was transforming the environment for his profit. Nobody cared what his activity do with environment and people continued with destruction of nature. Especially in 20th century nature suffered from development of industry and technology, then several ecological problems have appeared. Ecological problems:
Pollution
Air pollution is the biggest problem in large cities and in areas with concentrated industrial production. Factories, power stations and motor vehicles pump large quantities of carbon dioxide(CO2), sulphur dioxide (SO2) and nitrogen oxide (NO) and other gases into the air. This is a major cause of the changes in the environment which can lead to climate changes. Soil can be contaminated as a result of industrial waste and other causes. Much domestic rubbish is disposed of in landfills.

Acid rain
Some poisonous gases dissolve in water in the atmosphere and then fall to the earth as acid rain. Acid rain damages trees and buildings, and can kill fish in lakes and rivers. Rivers can also be polluted by industrial waste from factories and chemical fertilizers and pesticides used by farmers.

Global warming
Global warming is caused by the greenhouse effect. Normally, heat from the sun warms the earth and then escapes back into space. But carbon dioxide and other gases in the atmosphere trap the sun´s heat, and this is slowly making the earth warmer. The result is a rising temperature. The temperature of the earth could rise by 3°C over next 50 years. This may cause drought in some parts of the world, and floods in others, because artic ice begins to melt and sea levels rise.

Deforestation
Rainforests help to control global warming because they absorb carbon dioxide. In recent years, large areas have been destroyed, as the trees are cut down for wood or burned to clear the land for farming. The burning releases large amounts of carbon dioxide into the atmosphere. Many rainforests grow on poor soils, and when they are cut down or burned, the soils is washed away in the tropical rains. So that the area may turn to desert. Many plant and animal species that live there could become exctinct.

Ozone hole
Scientists have recenly discovered holes in the ozone layer. Ozone layer helps to protect the earth from the sun´s ultraviolet radiation, which can damage our skins and cause cancer. Ozone holes are caused by substances called CFCs (chlorofluorocarbons).