The Trump administration has blocked work that is central to major international climate change research, and barred federal scientists and diplomats from attending a key global climate event in China next week, according to three sources close to the situation who spoke to The Washington Post on condition of anonymity because they were not authorized to speak publicly. Katherine Calvin, NASA’s chief scientist and senior climate adviser, has been barred from traveling to China to meet with colleagues on work related to the next major report from the Intergovernmental Panel on Climate Change, a United Nations body that makes regular...