Biblically speaking, the Bible hasn't made a prediction as to when, however, it has given us signs to watch for. "We're still here" because some prophesies are still unfulfilled, some are in the process of happening right now.
@Hugh Dowling I believe decline is of course not related solely to human activity, but also a variety of unavoidable "natural" causes. For example, and it may not be a very good one, no vaccine has yet been found for Plasmodium , the Malaria-causing parasite (2015 stats.: 300 million cases, 1 million deaths). Those getting no treatment are most likely to succumb to the disease. 300 million is what, 1/16 of Earth's human population? Frank