The term 'of global extremes' refers to the two most extreme points on the planet, the North and South Poles. The crossword solution for this term is 'POLAR, ' which is a five-letter word that describes the two points of the Earth that are farthest from the equator. The North Pole is located in the Arctic Ocean, while the South Pole is located in Antarctica. Both poles are characterized by extreme cold temperatures and long periods of darkness during winter months.