First, the aggregate balance sheet of major central banks started to shrink earlier in the year, a reversal that took investors many months to notice but judging by recent market volatility, it is finally being fully appreciated.

Second, beginning this month the Fed's bond portfolio run-offs as part of its QT are roughly offsetting the combined tapered net QE purchases by the ECB and BoJ. Worse, QT is now set to dominate.

Some facts: between mid-2008 and early 2018, the "Big-6" central banks expanded their balance sheets by nearly $15tn, most of it due to explicit targeted purchases of domestic assets (QE) in addition to other forms of liquidity injections (collateralised lending such as the ECB's TLTROs or FX interventions equivalent to foreign-asset QE).

According to Deutsche Bank estimates, the four major central banks involved in QE (Fed, ECB, BoJ and BoE) are now collectively holding $11.3tn of securities accumulated through their asset purchase programs.