Sentence:  It is tempting to speculate about the incentives or compulsions that might explain why anyone would take to the skies in [the] basket [of a balloon]: [...];  [...]; or perhaps to muse on the irrelevance of the borders that separate nation states and keep people from understanding their shared <WSD>environment</WSD>. 
Meaning of the word marked with <WSD> tags:  The natural world or ecosystem.