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Title: Green transition, investment horizon, and dynamic portfolio decisions Authors:  Willi Semmler - New School for Social Research (United States) [presenting]
Ibrahim Tahri - PIK (Potsdam Institute for Climate Impact Research) (Germany)
Joao Braga - New School (Germany)
Abstract: The purpose is to analyze the implications of investors' short-term oriented asset holding and portfolio decisions (or short-termism), and its consequences on green investments. We adopt a dynamic portfolio model, which, contrary to conventional static mean-variance models, allows us to study optimal portfolios for different decision horizons. Our baseline model contains two assets, one asset with fluctuating returns and another asset with a constant risk-free return. The asset with fluctuating returns can arise from fossil-fuel-based sectors or from clean energy-related sectors. We consider different drivers of short-termism: the discount rate, the nature of discounting (exponential vs hyperbolic), and the decision horizon of investors themselves. We study first the implications of these determinants of short-termism on the portfolio wealth dynamics of the baseline model. We find that portfolio wealth declines faster with a higher discount rate, with hyperbolic discounting, and with a shorter decision horizon. We extend our model to include a portfolio of two assets with fluctuating returns. For both model variants, we explore the cases where innovation efforts are spent on fossil fuel or clean energy sources. Detailing dynamic portfolio decisions in such a way may allow us for better pathways to empirical tests and may provide guidance to some online financial decision-making.