The consensus on the street is not "if" the tapering will commence but "when". And it is this consensus that has roiled markets over the past week. Particularly hard hit have been Emerging Markets and their currencies as concerns mount about whether they will be able to finance their current account deficits in a rising rate environment.
The debate rages regarding why rates have been rising. Some, like economist Scott Grannis, argue here http://scottgrannis.blogspot.com/2013/08/three-cheers-for-higher-yields.html that rising rates we are presently experiencing are the normal result of an improving economy and not because of market fears that tapering will slow the economy.
It's difficult taking an opposing position to Scott as he's been "spot on" on every position he has taken since the market bottom in 2009. Nevertheless, my concerns surround the rate of increase in rates since May 1st. Below is a daily line chart of the Ten Year US Treasury yield since September, 2008: