What will the world look like about two decades from now? Obviously, nobody knows, but some things are more likely than others. Companies and governments have to make informed guesses, because some of their investments today will last longer than 20 years. In December, the United States National Intelligence Council published its guess: Global Trends 2030: Alternative Worlds.

The NIC foresees a transformed world, in which "no country - whether the US, China, or any other large country - will be a hegemonic power". This reflects four "megatrends": individual empowerment and the growth of a global middle class, diffusion of power from states to informal networks and coalitions, demographic changes owing to urbanization, migration and aging, and increased demand for food, water and energy.

Each trend is changing the world and "largely reversing the historic rise of the West since 1750, restoring Asia's weight in the global economy, and ushering in a new era of 'democratization' at the international and domestic level". The US will remain "first among equals" in hard and soft power, but "the 'unipolar moment' is over".

It is never safe, however, to project the future just by extrapolating current trends. Surprise is inevitable, so the NIC also identifies what it calls "game-changers", or outcomes that could drive the major trends off course in surprising ways.

First among such sources of uncertainty is the global economy: Will volatility and imbalances lead to collapse, or will greater multipolarity underpin greater resilience? Similarly, will governments and institutions be able to adapt fast enough to harness change, or will they be overwhelmed by it?

Moreover, while interstate conflicts have been declining, intrastate conflicts driven by youthful populations, identity politics and scarce resources will continue to plague some regions like the Middle East, South Asia and Africa. And that leads to yet another potentially game-changing issue: whether regional instability remains contained or fuels global insecurity.

Then there is a set of questions concerning the impact of new technologies. Will they exacerbate conflict, or will they be developed and widely accessible in time to solve the problems caused by a growing population, rapid urbanization and climate change?

The final game-changing issue is America's future role. In the NIC's view, the multi-faceted nature of US power suggests that even as China overtakes America economically - perhaps as early as the 2020s - the US is most likely to maintain global leadership alongside other great powers in 2030. "The potential for an overstretched US facing increased demands," the NIC argues, "is greater than the risk of the US being replaced as the world's pre-eminent political leader."