Option 1 -> "is suffer" is grammatically incorrect - base form cannot follow "is" in this context.
Option 2 -> "is suffers" is grammatically incorrect - cannot combine auxiliary verb "is" with third person singular form.
Option 3 -> "is suffered" would be passive voice, but "suffer from" doesn't work in passive construction here.
Option 4 -> "is suffering" forms present continuous tense, correctly showing the ongoing action.
Hence, Option 4: suffering -> The sentence requires present continuous tense (is + verb-ing) to indicate that the world is currently and continuously suffering from climate change. The structure "is suffering from" is grammatically correct and contextually appropriate to describe the ongoing crisis. -> correct