We live in a world that is very interconnected. Air and Water move freely across the planet. Water that evaporates from one part of the earth returns to some other part as rain or snow, ever so often causing devastating floods and snowstorms. Ice that melts from our polar caps raises sea levels and can cause whole islands to be submerged. Causes of Global Warming in one part of the world can have catastrophic effects on another.
When local rain forests are cut down to expand habitats for humans or for local economic reasons the reduction of Oxygen in our athmosphere is global. While it may only be the developed and emerging countries that spew carbon emissions into the atmosphere the impact is global with countries like the Maldives bearing the brunt for no significant contribution of carbon emissions of their own.