Not surprisingly, the news has precipitated another round of quasi-Malthusian musings: Can the planet support 10 billion people? This is certainly a legitimate question, but the focus on the global picture -- which really hasn't been significantly affected by the update -- obscures the real news in the update.
As the Economist notes:
The most dramatic changes are national, not global. America's population, now 310m, is likely to rise to 400m in 2050 and 478m in 2100. China's is forecast to fall by 400m between now and 2100. Russia’s population is now 142m; Afghanistan’s slightly more than a fifth of that; Niger’s barely a tenth. But by 2100, Afghanistan is forecast to have the same population as Russia (111m) and Niger will be larger. Such forecasts need to be taken with a bucketload of salt: tiny shifts in today’s birth rate extrapolated over 90 years produce huge changes. But the general picture is probably right. Sub-Saharan Africa’s current population, at 856m, is little more than Europe’s and a fifth of Asia’s. By 2050 it could be almost three times Europe’s and by 2100 might even be three-quarters of the size of Asia. By any measure, Africa is by far the fastest-growing continent.
The most eye popping element is the rapid decline in China's population -- the result of the one child policy playing itself out over time. Two major lessons come to mind: 1) major transformations to social systems can be consciously planned and implemented when there is the political will but 2) successful implementation plays itself out in a span of decades rather months. In other words, such transformations are much harder in social systems dominated by quarterly-returns and the horse race politics of seemingly constant elections.