GIBRAN NAIYYAR PESHIMAM THE world's richest countries have not done enough to combat global warming, Pakistani Prime Minister Imran Khan has said, adding his country had done more than any other in the world to combat rising emissions relative to its economic means. Pakistan, this year's host of the United Nations' annual World Environment Day on June 5, is among the countries worst affected by climate change, having been regularly hit by devastating floods in recent years, displacing hundreds of thousands of people and destroying swathes of agricultural land. "Has the developed world done enough: The answer is no," Khan…