MADRID/LONDON: Scores of world leaders will be sweltering in the summer sun of southern Spain next week at a once-a-decade United Nations development financing summit aimed at curbing global poverty, disease and the worst-case threats of climate change. Despite the scorching temperatures, though, a major chill looms over the event – the decision early this month by the United States, traditionally the world’s largest aid giver and key finance provider, not to show up.