On the agenda is life on earth, in all its forms and diversity. The big question is how far nations will go to stop the disastrous declines underway. Representatives from more than 175 countries are gathering to negotiate answers, starting on Monday in Cali, Colombia, at what is expected to be the largest United Nations biodiversity conference in history. How the talks unfold over the next two weeks will help determine, for better or worse, the planet’s future. Biodiversity is declining faster than at any time in human history, an intergovernmental panel of scientists found in 2019. It estimated that...