Tackling the problem of emissions is at the forefront of scientific research today. While industrial engines designed to operate in stable regimes produce emissions, attempts to operate them at "greener" conditions often fail due to thermoacoustic instability. During thermoacoustic instability, hazardous high amplitude periodic oscillations lead to failure of these engines in power plants, aircrafts and rockets. Yet, identifying the onset of thermoacoustic instability remains elusive due to spatial variability and the continuous evolution of spatiotemporal patterns in the reacting flow field. Here, we show experimental evidence of early manifestation of the onset of thermoacoustic instability at certain zones. Our findings allow us to identify a critical threshold that enables us to distinguish stable operating regimes from hazardous operations. This opens new perspectives for predicting the onset of thermoacoustic instability and could be a step forward to "greener" operations. The developed methodology is applicable for other systems exhibiting phase transitions.