Surprisingly few specific long-range economic forecasts exist. The IPCC made some in order to drive their energy and environmental forecasts. They forecast GDP growth of 7-fold between 1990 and 2050 and 24-fold by 2100. The numbers for industrialized countries are 5-fold and 13-fold, and those for developing countries are 14-fold and 69-fold (IPCC, 1995, Volume 2: 590).
It is common to forecast that recent growth rates of about 10 percent per year for China and other Asian “tigers” will continue for some time as they close income per capita gaps with developed Western economies and that the Chinese economy will therefore become the largest in the world. Paul Krugman has been more skeptical, arguing that the easy period of growth for many Asian countries, in which they have used high savings rates to mobilize capital, is reaching an end; those countries may need substantial internal transformations in the next phases of growth. The former Soviet Union was able to achieve rapid growth in a similar early phase of capital mobilization, but proved unable to sustain growth with fundamental social transformations.
Angus Maddison (1995) has studied global economic growth over the 1820-1992 period in a manner that could theoretically facilitate forecasting. He emphasizes the role of technological progress in the leading state and of catch-up processes in followers. This model suggests, however, that the key variable for the future is technological progress in the leader(s), and that seems nearly impossible to forecast. There is, however, evidence that such progress has accelerated over time - the period of most rapid growth since 1820 was 1950-1973, the second most rapid was 1870-1913, and the third most rapid was 1973-1992.
Models. The IMF maintains an econometric model called MULTIMOD, primarily for developed countries, focused on inflation. See www.imf.org/external/np/res/mmod/mark3/index.htm.