Why do we consider the fact …

Environmental degradation is currently a global issue that is the core subject matter of discussions and debates all over the world. The fact is that environmental degradation cannot be restricted by the national or state boundaries to a specific area or location that is causing such degradation may be. Its consequences are felt in the surrounding states or nations or sometimes globally as well.
For instance, let's take the example of air pollution. Air pollution through massive thermal power plants and other industries, in India, may cause pollution in Pakistan, Sri Lanka, etc.
Thus, our neighbours also experience an increase in asthma and other respiratory diseases due to pollution mainly caused by us. Acid rain, climate change, etc. are some issues which are transcontinental consequences. Deforestation in Brazil (the Selvas) has caused a disturbance in the rainfall pattern throughout South America.
Land degradation and conditions like a dam - burst in China affect India and Bangladesh as it causes massive silt deposition and floods. Now, environmental protection is a major issue globally and is taken seriously by almost all countries. Discussions take place on international levels among environmentalists and heads of states to fight the menaces.