Early coal mines lacked ventilation systems, so miners brought caged canaries into new seams to detect the presence of methane and carbon monoxide. If a canary stopped singing – or worse, died – the mine would be evacuated until the dangerous gas buildup could be cleared. Other animals were tried for this purpose, but canaries have become recognized for their natural ability to detect small but potentially lethal concentrations of toxicity.

The recent string of surprise downside moves in markets may be the canary in the coal mine for global investors. Ongoing monetary stimulus is leading to heightened volatility, and the bull market which has been in place since 2009 is becoming overextended.