The Sydney climate causes human remains to mummify, according to groundbreaking results from Australia's first body farm that challenge conventional science used to establish time of death in police investigations.

The tendency of human remains exposed in bush near the Blue Mountains to dry out and mummify rather than decompose was so surprising that the facility's director Shari Forbes repeated the studies "across all seasons and several years" to ensure the data was accurate.

It is the first study of the deterioration of human remains in the local climate. The findings challenge the science currently used to establish time of death in murder and missing person investigations.

The study found that the remains of pigs, used in the past by forensic scientists as a proxy to simulate decomposition in human remains, were unreliable in the Australian environment. Pig remains have been used to establish time of death of victims of crime or disasters.

Dr Forbes said that the Australian research found that human decomposition was "an extremely variable process, even between individuals of similar physiology placed in the same environment."