First paragraph: Environmental tipping points occur when there are step changes in the way the biophysical world works – whether loss of soil fertility, collapse of a fishing stock, or sudden changes in weather patterns, such as those that caused the grasslands in North Africa to become deserts, 6000 years ago. These non-linear shifts arise following a critical degree of change, resulting from either many small cumulative changes or one large shock, “tipping” the system over a threshold and into a new stable state. Entering an alternative stable state is associated with a change to system function, usually being difficult to reverse or “tip” back into the original state. Increasingly we recognise that human-environment interactions are affecting the likelihood that critical thresholds for tipping points will be crossed, leading to step-changes in the provision of environmental goods and services, and impacting upon food security
