Answer:
(This is only very brief)
Environmental issues are created by the earth as a whole which includes all the countries within it therefore making environmental issues global issues. No country alone has caused global warming. This also means that no country alone is able to single-handedly defeat an environmental issues which have now spiralled out of control. No one has enough resources, that's why it would be better if there was a global intervention for environmental issues because the more brain power and resources, the better.