““[A] group of leading academics argue that humanity must stay within defined boundaries for a range of essential Earth-system processes to avoid catastrophic environmental change. . . . They propose that for three of these—the nitrogen cycle, the rate of loss of species and anthropogenic climate change—the maximum acceptable limit has already been transgressed. In addition, they say that humanity is fast approaching the boundaries for freshwater use, for converting forests and other natural ecosystems to cropland and urban areas, and for acidification of the oceans. Crossing even one of these planetary boundaries would risk triggering abrupt or irreversible environmental changes that would be very damaging or even catastrophic for society.””
