This paper investigates a possibly fundamental aspect of technological progress. If knowledge accumulates as technology advances, then successive generations of innovators may face an increasing educational burden. Innovators can compensate through lengthening educational phases and narrowing expertise, but these responses come at the cost of reducing individual innovative capacities, with implications for the organization of innovative activity—a greater reliance on teamwork—and negative implications for growth. Building on this “burden of knowledge” mechanism, this paper first presents six facts about innovator behaviour. I show that age at first invention, specialization, and teamwork increase over time in a large micro-data set of inventors. Furthermore, in cross-section, specialization and teamwork appear greater in deeper areas of knowledge, while, surprisingly, age at first invention shows little variation across fields. A model then demonstrates how these facts can emerge in tandem. The theory further develops explicit implications for economic growth, providing an explanation for why productivity growth rates did not accelerate through the 20th century despite an enormous expansion in collective research effort. Upward trends in academic collaboration and lengthening doctorates, which have been noted in other research, can also be explained in this framework. The knowledge burden mechanism suggests that the nature of innovation is changing, with negative implications for long-run economic growth.

Great achievements in knowledge are produced by older innovators today than they were a century ago. Nobel Prize winners and great inventors have become especially unproductive at younger ages. Meanwhile, the early life cycle decline is not offset by increased productivity beyond middle age. The early life cycle dynamics are closely related to age when the PhD was received, and I discuss a theory where knowledge accumulation across generations leads innovators to seek more education over time. More generally, the narrowing innovative life cycle reduces, other things equal, aggregate creative output. This productivity drop is particularly acute if innovators' raw ability is greatest when young. © 2010 The President and Fellows of Harvard College and the Massachusetts Institute of Technology.

Human capital differences across countries can appear large or small depending on measurement methods. This Reply clarifies key assumptions and conceptual distinctions across accounting approaches. Accounting-based arguments for small human capital differences are difficult to sustain. By contrast, large human capital differences are theoretically and empirically coherent. Non-accounting arguments against large human capital variation are examined and their weaknesses pinpointed. This Reply also suggests a fruitful way forward for this literature, providing a natural conception of human capital that integrates literatures on ideas and institutions with the accounting of Jones (2014). (JEL E24, I26, J24, J31)

This paper presents a new framework for human capital measurement. The generalized framework can (i) substantially amplify the role of human capital in accounting for cross-country income differences and (ii) reconcile the existing conflict between regression and accounting evidence in assessing the wealth and poverty of nations. One natural interpretation emphasizes differences across economies in the acquisition of advanced knowledge by skilled workers.

Economic growth within countries varies sharply across decades.This paper examines one explanation for these sustained shifts in growth-changes in the national leader.We use deaths of leaders while in office as a source of exogenous variation in leadership, and ask whether these plausibly exogenous leadership transitions are associated with shifts in country growth rates.We find robust evidence that leaders matter for growth.The results suggest that the effects of individual leaders are strongest in autocratic settings where there are fewer constraints on a leader's power.Leaders also appear to affect policy outcomes, particularly monetary policy.The results suggest that individual leaders can play crucial roles in shaping the growth of nations."There is no number two, three, or four . . .

A rapidly growing body of research applies panel methods to examine how temperature, precipitation, and windstorms influence economic outcomes. These studies focus on changes in weather realizations over time within a given spatial area and demonstrate impacts on agricultural output, industrial output, labor productivity, energy demand, health, conflict, and economic growth, among other outcomes. By harnessing exogenous variation over time within a given spatial unit, these studies help credibly identify (i) the breadth of channels linking weather and the economy, (ii) heterogeneous treatment effects across different types of locations, and (iii) nonlinear effects of weather variables. This paper reviews the new literature with two purposes. First, we summarize recent work, providing a guide to its methodologies, datasets, and findings. Second, we consider applications of the new literature, including insights for the “damage function” within models that seek to assess the potential economic effects of future climate change. (JEL C51, D72, O13, Q51, Q54)

This paper investigates the remarkable extremes of growth experiences within countries and the changes that occur across growth transitions. We find two main results. First, virtually all but the very richest countries experience both growth miracles and failures over substantial periods. Second, growth accelerations and collapses are asymmetric phenomena. Collapses typically feature reduced investment amidst increasing price instability, whereas growth takeoffs are primarily associated with large expansions in international trade. The results show that even very poor countries regularly grow rapidly, but sustaining growth is difficult and may pose a very different set of challenges than starting it. Copyright by the President and Fellows of Harvard College and the Massachusetts Institute of Technology.

This paper uses international trade data to examine the effects of climate shocks on economic activity. At the aggregate level, Melissa Dell, Benjamin F. Jones, and Benjamin A. Olken (2008) (hereafter, DJO) have demonstrated that higher temperatures in a given year reduce the growth rate of GDP per capita, but only in poor countries. The analysis of trade data in this paper builds on that finding, with three principal motivations. First, international trade links the fortunes of countries, providing potentially important conduits for geographically limited climatic impacts to have global economic effects. Second, international trade data is the best available source for identifying economic activity worldwide separately by narrowly defined sectors. Examining international trade data, one can thus say more precisely what sectors are affected by climatic changes. Finally, the trade data, collected by the importing country, provides a check on the potentially low-quality national accounts data provided by the home country.

Temperature and Income: Reconciling New Cross-Sectional and Panel Estimates by Melissa Dell, Benjamin F. Jones and Benjamin A. Olken. Published in volume 99, issue 2, pages 198-204 of American Economic Review, May 2009

Technological advance is often embodied in capital inputs, like computers, airplanes, and robots. This paper builds a framework where capital inputs advance through (i) increased automation and (ii) increased productivity. The interplay of these two innovation dimensions can produce balanced growth, satisfying the Uzawa Growth Theorem even though technological progress is capital-embodied. The framework can further address structural transformation, general-purpose technologies, the limited macroeconomic impact of computing, and declining productivity growth and labor shares. Overall, this tractable framework can help resolve puzzling tensions between micro-level observations of innovation and balanced growth while providing new perspectives on numerous macroeconomic phenomena. (JEL E22, E23, E24, E25, L16, O33, O41)