Beyond GDP: Modelling labour supply as a "free time" trade-off in a multiregional optimal growth model

In this paper we develop the standard utility function of a Ramsey-type optimal growth model to account for a market-time vs. free-time trade-off. To do so, we introduce a free-time preference coefficient that measures the utility gained by deviating from a maximum labour supply defined as the combination of a 95% labour force participation rate for the 20 to 69 year-old population, and 3000 annual working hours (50 effective 60-hour weeks). We calibrate this free-time preference coefficient for 12 world regions on statistical and projected data from the United Nations, the International Labour Organisation and the OECD. We illustrate a prospective use of this modelling development by comparing the consequences of convergence of the free-time preference coefficients of all world regions to the contrasted Western European vs. United States value. Over the 21st century, compared to a business-as-usual trajectory defined by maintained regional disparities in free time preference, convergence to US free time preference induces a 0.3% decrease in global discounted labour market time, but a 4.2% increase in discounted global GDP sustained by a 2.5% increase in primary energy consumption that translates into a 1.7% increase in cumulated CO2-equivalent emissions; convergence to Western European free time preference decreases labour market time by 13.8%, GDP by 11.7%, primary energy consumption by 10.7% and cumulated CO2-equivalent emissions by 9.1%.