That statistic of 50% professors being adjunct is not cited, and from searching online appears to come from the SEIU, which is a group who's goal is to unionize adjunct faculty. The report it self is not available, and it has been quoted in articles as "part-time faculty held 50 percent of teaching jobs at colleges" [1] and "adjuncts held 50 percent of teaching jobs at colleges" [2]

Neither of those statements are the same as "Adjuncts now make up well over 50 percent of the faculty at colleges and universities." as stated in the article.

[1]http://www.boston.com/yourcampus/news/bentley/2013/06/as_ben...

[2] http://www.boston.com/yourcampus/news/tufts/2013/07/adjunct_...