Earth at risk

摘要

CARL SAGAN described Earth, seen from afar, as a pale blue dot. Tiny and insignificant it may look, but this blue dot has provided us with a remarkably stable environment for almost 12,000 years. Humans have pushed Earth close to, and possibly beyond, its ability to support us long term. On several fronts, we have gone beyond what are regarded as "limits" for vital systems, such as biodiversity'and the nitrogen cycle. On others, we are nearing the danger zone. Climate change is the most pressing example.