A very interesting theoretical paper "Labor Mobility within Currency Unions " by Emmanuel Farhi and Iván Werning, April 2014 (http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2436714) looks at "the effects of labor mobility within a currency union suffering from nominal rigidities."
The departing point for the paper is Mundell (1961) famous dictum that labor mobility must be a precondition for optimal currency areas. In support of this dictum, the U.S. "enjoys relatively high mobility and has proven to be a successful currency union. Mobility is arguably much lower within the Eurozone, which sunk into trouble scarcely ten years after its inauguration." Of course, despite the shallower extent of mobility in Europe, EU policymakers repeatedly cite free mobility regime for labour within the EU as a major cornerstone of the EU and, thus, by corollary - to the functioning or the promise of functioning of the euro zone.
Despite all the intuition behind Mundell's proposition, there is little formal research connecting mobility with macroeconomic adjustments in a currency union setting.
Farhi and Werning "set up a currency union model featuring nominal rigidities and incorporate labor mobility across the different regions (or countries) that compose the currency union." The paper tackles "…two related questions. First, does mobility help stabilize macroeconomic conditions across regions in a union? Second, is equilibrium mobility socially optimal?"
The study does not quite confirm Mundell's proposition, but its findings "…are consistent with a potential important role for mobility. Workers migrating away from depressed regions naturally benefit from the option to pick up and go somewhere better. The interesting and less obvious question is whether their exodus also helps those that stay behind. That is, whether it aids in the macroeconomic adjustment of regions. A major insight of our analysis is that the answer to this question is subtle because workers leaving a region depart not only with their labor, but also with their purchasing power."
This leads to a divergent set of outcomes depending on the source of the original shock to the economy. If the demand shock comes from internal (region-specific) shock (like, for example, in the case of Ireland where property crash led to massive disruptions in domestic demand and where domestic demand continued to shrink every year since 2008, uninterrupted), the authors find that "…migration may not help regional macroeconomic adjustment." How so? "…we provide a benchmark case where migration has no effect on the per-capita allocations across regions. For this benchmark, the entire demand shortfall in depressed regions is internal, located within the non-tradable sector [again, think Irish construction, property and retail sectors, and associated banking sector bust]. When workers migrate out of a depressed region local labor supply is reduced, but so is the demand non-traded goods, which, in turn, lowers the demand for labor. The two effects cancel, leaving the situation for stayers unchanged."
In contrast, "…when external demand is also at the root of the problem, migration out of depressed regions may produce a positive spillover for stayers." This, of course, applies to economies like Portugal and Cyprus, where external shocks are the main drivers for the crisis. When depressed regions also suffer from external demand shortfalls, "…migration out of depressed regions may help improve the region’s macroeconomic outcome. For example, at the opposite end of the spectrum, suppose regions only produce traded goods and that there is no home bias in the demand for these goods. The demand for each region’s product is then determined entirely by external demand at the union level, and internal demand plays no special role. In this case, migration out of a depressed region improves the outcome of stayers by increasing their employment, income and consumption."
On a positive side, from Ireland's point of view: "…the degree of economic openness (how much regions trade with one another) turns out to be a key parameter. Openness was proposed by McKinnon (1963) as another precondition for an optimal currency area." Except, of course, as we in Ireland are fully aware, openness can be real (e.g. Swiss exporting indigenous output that is matched by the MNCs exporting out of Switzerland) and accounting (e.g. Irish exports of ICT services or phrama).
Lastly, it is worth noting that the paper does not consider rigidities beyond those present in the pricing mechanisms. Thus, for example, labour laws are not included and neither are hiring practices or promotional practices that can severely skew flows of labour.