Evaluating Past Forecasts: Reflections on One Critique of The Limits to Growth

摘要

In early 2005 after completing four years of study, an international network of 1,500 specialists produced a massive study, The Millennium Ecosystem Assessment. The principal findings in their reports generally confirm the long-term forecasts made over three decades earlier in a 1972 book, The Limits to Growth by Donella Meadows and her colleagues. The main features of the Limits to Growth projections have also been supported by other scientific studies during the past decade. They are also confirmed increasingly in the media by the widespread and growing concern about global problems related to oil depletion, water scarcity, agricultural soil deterioration, fisheries collapse, species loss, and climate change. Despite this corroboration, the initial Limits to Growth report was met with a storm of criticism that has persisted among many decision makers down to the present. In addition, a general survey of policy makers, at least in the United States today, would probably show they are either totally uninformed about the substance of the Limits to Growth forecasts, or that they have a vague and general impression that the report was disproved long ago and is no longer worthy of serious consideration. What explains this contrast? There is basic confirmation of the Limits to Growth scenarios within the fields of physical and biological science while there is general disdain and disregard within the fields of economics and policy. This is a question of central importance for the Dahlem Workshop, which hopes to produce a body of analysis that will have a different fate. The question can be usefully addressed by examining several of its corollaries. What vocabulary is useful for describing forecasting efforts and their products? What is the role of scenarios like those prepared by the Limits to Growth team? Why are the Limits to Growth conclusions still debated and criticized, after they have been generally confirmed by physical and biological developments on the planet? What would be the criteria and the procedures relevant for someone who is honestly trying to evaluate forecasts like those presented in Limits to Growth? What motivations prompt those who criticize such work? What lessons can we learn that will raise the quality and the impact of any forecasts that emerge from this Dahlem Workshop process? In this chapter I first present a brief glossary of terms useful in describing and evaluating efforts to foretell the future. Then I summarize the main features of the original Limits to Growth forecasts and compare those forecasts with scientists' current understanding of the global situation as summarized most recently in the Millennium Ecosystem Assessment. I examine one early and influential criticism of the Limits to Growth report-a major magazine article by Peter Passell and two colleagues, academic economists in the U.S. I list the various ways in which these three authors sought to dispute our analyses and discredit our team. I offer a conceptual perspective that is useful for understanding the role of forecasts in the evolution of social policy. Finally, I provide a list of seven concrete steps the IHOPE participants could take when releasing their report. The goal of all this is to provide the 96th Dahlem Workshop participants with information and perspectives that will help them increase the value and the impact of their work to develop better foundations for describing the integrated history and the future of people on Earth.