In the early 1970s, MR editors Harry Magdoff and Paul Sweezy increasingly introduced ecological themes into the magazine, and began to question the viability of unlimited, exponential economic growth in a limited biosphere. Sweezy, in particular, was deeply interested in ecological problems, a topic he began to write on in this period, in essays such as "Cars and Cities"…, and to which he returned on various occasions until the end of his life.… [In this 1974 letter to the influential ecological economist, Nicholas Georgescu-Roegen, Sweezy outlined] the revolutionary implications of ecology, and the break that these necessitated with pure "economism"—a rupture that only a truly revolutionary socialism could bring about.Click here to purchase a PDF version of this article at the Monthly Review website.