BRUSSELS — The EU’s top climate envoy is picking a fight with China weeks before a high-stakes United Nations summit on global warming, already undercut by the United States’ withdrawal from the 2015 Paris Agreement. Some diplomats and observers were left wondering what Wopke Hoekstra hoped to achieve when he attacked Beijing last month for what he described as a “clearly disappointing” climate plan — especially after the EU had failed to present its own strategy. The move raised fears of a