【論文】（10/09更新）

要旨：This paper investigates the elusive role of productivity heterogeneity in new trade models in the trade and environment nexus. We contrast the Eaton-Kortum and the Melitz models with firm heterogeneity to the Armington and Krugman models without heterogeneity. We show that if firms have a constant emission share in terms of sales — as they do in a wide range of trade and environment models — the three models’ emission predictions exactly coincide. Conversely, if firms have a constant emission intensity per quantity — a prominent alternative in the literature — the emission equivalence between the three models breaks. We provide a generalization that nests both constant emission shares in sales and constant quantity emission intensities as special cases. We calibrate the models to global production and trade data and use German firm-level data to estimate the key elasticity of how emission intensity changes with productivity. Our multi-industry quantification demonstrates that the role of firm heterogeneity depends both on the model and the estimated parameters. Moving from the Armington model to the EK model increases the emissions effect on trade, while moving from the Krugman model to the Melitz model decreases the emission effects on trade.

座長練習者：関口 格（京都大学）

1700-1730 “Herding in Equity-Based Crowd Funding” 松下 旦 (京都大学)

1730-1800 “Facilitating trust and trustworthiness: The impact of mediation” 千葉 早織 (京都産業大学)

Title: Structural Change in Production Networks and Economic Growth

Abstract：We study structural change in production networks for intermediate inputs (input-output network) and new capital (investment network). For each network, we document that the share of output produced by goods sectors has declined since the 1950s, offset by a rising fraction of production by services sectors. We develop a multi-sector growth model to study these trends and show that our framework admits an aggregate balanced growth path with such structural change. Calibrating the model using disaggregated expenditure-side price data for the United States, we find that inputs to intermediates production are complements. However, in contrast to existing literature, we find that inputs to investment production are substitutes. Hence, structural change in production networks implies that resources endogenously reallocate to the slowest growing intermediates producers and the fastest growing investment producers. As a result, we show that investment-specific technical change accounts for an increasing share of U.S. aggregate growth, rising from 30-40% of growth prior to the 1980s to more than 70% since the year 2000. In addition, more than 20% of aggregate growth after 2000 stems from endogenous reallocation induced by structural change. At the same time, productivity growth within the input-output network has stagnated, accounting for the bulk of the recent slowdown in aggregate growth.