First, from long term successful commodity trader Peter Brandt:
It has come to be known as the “risk-on/risk-off” or “all-one-market” phenomena in global markets. It is a situation where seemingly unrelated markets have taken on an historically high correlation. Individual markets seem to be the proxy for all other markets.
I have witnessed periods in the past when unusually strong correlations existed for months and months. But, I have never experienced the level of correlation we have lived with as traders since 2008.
via Chart of the Day: Decoupled from reason – macrobusiness.com.au