Frans Vera (2009, 29) explains the Shifting Baseline Syndrome as arising when:

• Each new generation does not know what ‘nature’ may have looked like before mankind started to impact upon it;

• The environment changes almost imperceptibly from generation to generation;

• Each new generation defines what is ‘natural’ according to its own experience of the (changed) environment it has encountered, and uses this as a baseline against which to measure changes in the environment.
  

As a result there is a continual lowering of the benchmark for what is ‘natural’ and the degraded state of the environment is considered to be ‘normal’. This means that society as a whole becomes very tolerant of creeping negative environmental change.