Nearly two-thirds of the world's population will live in cities by 2030, with most people middle class, connected by technology and protected by advanced health care, a report suggests.
That is the best-case scenario in the report, Global Trends 2030, released by the US government's National Intelligence Council. In the worst-case scenario, the rising population leads to conflict over water and food, especially in the Middle East and Africa, and the instability contributes to global economic collapse.
The study is the intelligence community's analysis of where current trends will take the world in the next 15 to 20 years, intended to help policymakers plan for the best and worst possible futures.
One bright spot for the US is energy independence. "With shale gas, the US will have sufficient natural gas to meet domestic needs and generate potential global exports for decades to come," the report said.
Among the major trends: the rise of a global middle class that is better educated, connected via technology and healthier due to advances in medicine. Power will no longer reside with one or two key nations but be spread across networks and coalitions of countries.
In countries with declining birth rates and an ageing population like the US, economic growth may slow, while 60% of the world's population will live in cities. Food, water and energy will be more scarce.
"Nearly half of the world's population will live in areas experiencing severe water stress," the report said.
Among the anticipated crises is the worry of global economic collapse, fighting among nations that do not adapt rapidly enough and the possible spill-over of instability in the Middle East and South Asia to the rest of the world.
Technology is seen as a potential saviour to head off some of this conflict, boosting economic productivity to keep pockets filled despite rising population, rapid growth of cities and climate change.
The report warns of the mostly catastrophic effect of possible "Black Swans", extraordinary events that can change the course of history. These include a severe pandemic that could kill millions in a matter of months and more rapid climate change that could make it hard to feed the world's population.