The National Academies Press recently published the report of a workshop on "The Arc of the Academic Research Career: Issues and Implications for U.S. Science and Engineering Leadership" (you can download the report as PDF for free from their website or read it online here). The report first highlights the current unstable arc in academic reserch careers before discussing the economics of early careers, the timing of tenure, incentives for retirement and "the other academe", especially given the rise of 2-year community colleges as a place for undergraduate education.
The report touches on important points, including the rise in post-doctoral appointments and the increase in their length in the sciences. I wish it had specifically mentioned the growing trend in engineering fields for would-be assistant professors to first take a post-doc before joining the ranks of the tenure-track faculty, which illustrates the growing aversion to risk of university administrators, understandably wary of committing a tenure-track position to someone who, when (s)he applies, is still a doctoral student working under the supervision of a faculty member.
While this stage has existed for a long time in the sciences, a whole new stage in one's academic research career is being introduced in engineering. (Thankfully, it is still possible for engineering PhDs to skip it, but perhaps not for much longer.) The report does do a very good job highlighting the different career opportunities for science vs engineering PhDs, and in particular the availability of well-paying industry positions for the latter.
In itself, adding two more years to someone's training in order for that person to better demonstrate his/her originality and independence of thinking may not be a bad thing, but when you look at the science model this originates from, you quickly realize those post-docs often stay in their position for five years or more, perhaps in part due to the excess supply of PhDs, which makes it difficult for them to obtain the position they aspire to. (The NAP also has a report out on "The Postdoctoral Experience Revisited"; read it here.)
There is a lot of talk from the government and in the media about needing more advanced degrees in STEM in order to foster innovation, but when you look at the career trajectory of biology PhD students, for instance (at least the ones I knew when they were M.I.T. graduate students at the same time as I was), they usually spend 1-2 years as a technician in a research lab before applying to PhD programs, where they stay for about 6-7 years, and then spend 5-6 years as post-docs before obtaining either a tenure-track position or a job in a pharmaceutical lab. This means that when they first start earning some decent amount of money (charitably defined as more than what a B.S. in industrial engineering at Lehigh makes on average right after graduation at age 22) they are between 34 and 37.
Add 6-7 years on the tenure track and these students, who presumably were at the very top of their class as undergraduates (at least those who made it to M.I.T.), are well into their 40ies when they know whether they will stay at their current place of employment or get to do it all over again. Another interesting tidbit I learned from a comment on an old blog post of mine is that faculty members in the sciences are, at some institutions, expected to pay their own salary from their own grant money (the university gives them lab space, a prestigious affiliation and, from what I understand, some small sum. I hope that is not the norm.) This doesn't seem a particularly attractive career path to any undergraduate who thinks ahead.
Yet, with too many talented PhD students who serve as TAs for required undergraduate introductory courses and the like, it is hard how to change the incentives in the system. A possibility would be to make it easier for students to change paths without having to drop out at year 6 (or 9) of the PhD process without anything to show for it, or a Master's that, in the sciences, is well-known to be given to doctoral students who decided to leave instead of being a degree students aspire to. In Electrical Engineering at M.I.T., for instance, "Electrical Engineer" is a degree in between the Master's and the PhD, requiring 162 credits + thesis instead of 66 credits + thesis. (In the chapter "The Other Academe", the report also highlights the situation of adjunct faculty and faculty at community colleges, which typically do not require PhDs and often employs ABDs [All But Dissertations] from the nation's top universities.)
Curiously, the report also makes no mention of Professors of Practice, who seem to be these days a growing trend in universties eager to expose their students to seasoned industry professionals. While a degree between M.S. and PhDs would represent a better off-ramp for doctoral students who decided they're no longer interested in research after all, PoPs provide a valuable on-ramp for industry practitioners interested in academic experience. This is not in itself a "research career" (to echo the report's title), and so may seem to be off-topic, but it is an important academic position at research universities, and thus deserves some attention.
Doctoral students who may lose heart with the lengthy tenure-track process would gain the ability to return to the academic world once they have spend some time in industry, hopefully at higher salaries. PoPs also offer the advantage of 3-year employment and (I believe) benefits, without requiring a PhD degree, again because those faculty members are expected to teach and sometimes direct professional Master's programs. Personally I'd love to fewer adjunct, part-time positions and more full-time, 3-year, non-tenure-track positions, not only for seasoned industry professionals but also for more junior employees. (Do take a look at Figure 4.1 p.28 about the "adjunctification" of the U.S. faculty.) In other words, as the arc of the academic research career becomes multiple arcs, there needs to be more on- and off-ramps between the worlds of academia and non-academia.
While the report also shares a few words about the future of tenure, very little is made of new models, e.g., at Olin College, where tenure simply doesn't exist. Obviously this is not a model that can easily be implemented elsewhere, but my personal opinion is that a model where promotion to associate professor would come with guaranteed 10-year employment and tenure would only come with promotion to full professor would make far greater sense in aligning faculty's incentives and universities' interests. In particular, the downside of the current model is that you end up with career associate professors or terminal associate professors, i.e., associate professors who never got promoted to full, and I don't see how that is a good outcome.