If the Greenland ice core data is applicable the transition will take 10 - 20 years.  That's 10-20 years from the start of the transition, not 10-20 years from 2011.

It's impossible to accurately pin-point a starting date of a transition in a Complex System until after the transition is completed.  The abnormal, to expectation, weather and weather patterns and patternings since 2007/2008 suggests, to me, we're already 2 or 3 years into it.

She believed in nothing; only her skepticism kept her from being an atheist. -- Jean-Paul Sartre