2052 - A Global Forecast for the Next Forty Years using a mix of models

摘要

The book 2052 -A Global Forecast for the next Forty Years (Randers, 2012) contains a description of what the author sees as the most likely scenario for global population, GDP, consumption, and ecological footprint over the next 40 years. The 2052 forecast is a "Business As Usual" scenario - in the sense that it describes the global future that will result if global society continues to make decisions in the traditional way, based on short term cost minimization. The basic assumption underlying the forecast is that individuals, corporations and nations will continue to tend to choose solutions that serve their short term interest. The present paper focuses on the method used to arrive at the 2052 forecast. The starting point was the The Limits to Growth study of scenarios for the human ecological footprint and the causal structure of the World3 model. Exploratory work, based on data for the last 40 years, indicated that global wanning will become the tightest planetary constraint going forwards. The study therefore focused on CO2 emissions and their effects. In the first iteration, future CO2 emissions were estimated in an open-loop model (using the "linear core" of the revised causal structure). In the next iteration, the forecast was improved by including the effects of important, but un-modelled, feedback through manual iteration. The global forecast was obtained as the sum of separate forecasts for 5 world regions. In both stages external models (from the literature) were used to improve the quality of the forecast. But these models were not fused into one complete system dynamics model of global growth. Rather concepts and insights were borrowed wholesale, and consistency over time (and among regions) was sought through manual iteration, using spreadsheets. The paper elaborates the weaknesses in this procedure, but argues that it is still possible to arrive at a credible forecast for the next 40 years, and to conclude that world population and GDP will grow more slowly towards 2052 than commonly assumed, but still fast enough to trigger significant global warming.