Since before the Industrial Revolution, exponential economic growth has supported rising standards of living around the world. Everincreasing use of natural resources, notably energy from fossil fuels, has been key to the process. Climate change is a civilization-threatening consequence. Increasing temperature and more frequent natural disasters will impact the economy in many ways, inflicting damage on output and assets. Here we present a model of economic growth based on Keynesian aggregate demand theory to study how climate feedbacks affect the long-run evolution of the economy. Traditional growth theory attempts to explain sustained exponential increases of labor productivity and income. Early contributions such as Solow’s influential model focused on capital accumulation as the engine of growth. Capital deepening (a higher capital/labor ratio) supposedly allows workers to be more productive (Harrod, 1939; Domar, 1946; Solow, 1956). This tradition of growth theory sees technological progress — due to either scientific and technological developments external to the economy or investment in research and development — as the other main driver of growth. Innovations can be technological or organizational such as the division of labor across and within industries. Decreasing costs due to economies of scale also play a role (Smith, 1776). Potential output is determined by the size and skills of the labor force, the accumulated capital stock, and the available technology. In supply-driven mainstream models it will always be realized through full employment of the available resources. An important alternative conception of economic growth, based on Keynes’ theory of aggregate demand, developed in the work of Nicholas Kaldor, Michal Kalecki, and Joan Robinson, emphasizes demand as the immediate driver of production and income growth in capitalist economies. The model we present here combines such a short-run demand-determined model of output with a model (inspired by Kaldor’s thinking on economies of scale) of endogenous long-run technical change depending on the growth of output. We follow the Kaldorian tradition of linking capital accumulation with technological progress: high demand calls forth higher output and income, which over time lead to accumulation and provide a macroeconomic explanation for productivity beyond standard growth theory. An important strand of thought in ecological economics emphasizes that increasing labor productivity has historically gone hand in hand with rising productive use of energy (Taylor, 2008). Since the 19th century, fossil fuels have been the principal source (Georgescu-Roegen, 1975; Cleveland et al., 1984; Ayres and Warr, 2009). We extend the standard model of economic growth to allow for this productivity-energy link directly.