(i) The threat to the environment caused by pollution or by leakage of oil or gas does not remain restricted to one nation.
(ii) The visible effects of the decline of environment are extinction of species of plants and animals, decrease in the fertility of soil, water shortage, fluctuation in the proportion of rainfall, global warming, drying up of rivers and lakes, pollution of rivers and seas, incidence of newer diseases, acid rain, thinning of the ozone layer, etc.
(iii) Even if some of the effects are restricted to particular nations, these problems reach global proportions due to their long term effects, while some problems are inherently of a global nature.
