In addition, and perhaps even more significantly, more than 20 companies with space requirements of more than 2.5 million square feet have moved or will move into downtown Chicago from the suburbs since 2008 including United, BP and, most recently, Motorola Mobility, which completed the largest lease of 2012 — 572,000 square feet at The Merchandise Mart — following the company's acquisition by Google.

In all, the Chicago CBD saw its second consecutive year of modest positive net absorption in 2012 — a trend that seems likely to continue (and perhaps accelerate) in 2013 and 2014. And after bottoming out at around $30 in 2009, average gross rental rates should surpass $32 per square foot in 2013, a new all-time high.

Still, several factors threaten to forestall all the positive momentum.

Despite the many aforementioned companies that are aggressively adding jobs, many others have adopted a more conservative hiring/capital investment strategy while macroeconomic factors — the impending “fiscal cliff,” state and local budget crises, turmoil in the Middle East and the Korean Peninsula and the Euro crisis — have created a pervasive sense of uncertainty.

Also worth noting is the fact that companies are becoming more and more efficient in how they use office space. A recent Jones Lang LaSalle study of law firms, for instance, gave back an average of 17 percent of their space when signing a new lease. Companies in the financial services, high-tech, and marketing/advertising industries are often being even more aggressive, with shared workspaces and bench seating becoming the norm at many firms.

But even in spite of these headwinds, 2013 stands to be a year of improving economics for landlords as a lack of new inventory and gradually improving demand combine to drive down vacancy and put upward pressure on rental rates.

Steve Smith, managing director of Jones Lang LaSalle's landlord leasing practice in Downtown Chicago. The views expressed in this column are the author's own.