Once confined to the margins, the ecological critique of economic growth has gained widespread attention. At a United Nations climate-change summit in September, the teen-age Swedish environmental activist Greta Thunberg declared, “We are in the beginning of a mass extinction, and all you can talk about is money and fairy tales of eternal economic growth. How dare you!” The degrowth movement has its own academic journals and conferences. Some of its adherents favor dismantling the entirety of global capitalism, not just the fossil-fuel industry. Others envisage “post-growth capitalism,” in which production for profit would continue, but the economy would be reorganized along very different lines. In the influential book “Prosperity Without Growth: Foundations for the Economy of Tomorrow,” Tim Jackson, a professor of sustainable development at the University of Surrey, in England, calls on Western countries to shift their economies from mass-market production to local services—such as nursing, teaching, and handicrafts—that could be less resource-intensive. Jackson doesn’t underestimate the scale of the changes, in social values as well as in production patterns, that such a transformation would entail, but he sounds an optimistic note: “People can flourish without endlessly accumulating more stuff. Another world is possible.”