Why do environmental conditions change?

There are many reasons for changes in the environment. Environmental change can be sudden because of a meteorite impact or a volcanic eruption or it can be gradual like a
change in the climate. In the history of the Earth, there have been many sudden changes. Dust clouds and pollution darken and poison the
world and cause catastrophes. 

Slow changes in the environment such as changes in the sea level, ice ages, or torrential rains can be due to different reasons. For instance, parts of the earth are lifted as a result of the displacement of tectonic plates and therefore sea coasts shift. Today,  he environmental changes are mainly due to irresponsible human actions such as draining of marsh areas, cutting of trees, and air pollution.