In this Oct. 1, 2011 photo, tourists gather near an electric sign reading "the 62nd anniversary of the establishment of Republic of China" in Tiananmen Square in Beijing. For now, China remains the most populous nation, with 1.34 billion people. Nonetheless, its growth has slowed dramatically and the population is projected to start shrinking in 2027.
NEW YORK — In a cramped office on the 19th floor of Two United Nations, Danan Gu, a nerdy population analyst, found 7 million children in China who didn’t officially exist.
They materialized in front of him, on a desktop computer. Gu pulled up a chart from China’s 2000 census, showing children age 1 and under. Then he clicked on a Ministry of Education report that recorded students in the same age group about 10 years later.
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The numbers didn’t add up: 32 million students were in the schools, but only 25 million were counted in the census a decade earlier. The discrepancy didn’t surprise Gu, who emigrated from China and studied demographics at Duke University. Under the one-child policy, “parents hide children all the time,” he said.
Conjuring up uncounted people by cross-referencing census data with surveys and other statistics is a common trick of the demographics trade, one of several methods used recently by researchers at the U.N. Population Division to arrive at their landmark population projection: 7 billion people inhabiting Earth on Oct. 31.
Looking deeper into the cloudy future, the United Nations expects the world’s population to hit 9 billion in 2050, and, if current fertility levels ease downward as expected, surpass 10 billion at the start of the next century. Mortality rates have a lesser impact on population estimates because life expectancy is rising.
If fertility rates don’t decline, particularly in Africa and parts of Asia, the population could reach 27 billion next century, said the U.N. division’s chief, Gerhard K. Heilig. He called that projection a highly unlikely scenario that must nonetheless be considered.
The words could and would dominate population reports. The United Nations has no way of knowing for certain when the 7 billion milestone will be reached. Oct. 31 is a symbolic date based on population estimates dating back five years, according to an explanation on the division’s Web site. Projections have at least a 1 percent margin of error, meaning the population can be reached six months before a target date or six months after.
The United Nations is regarded in most quarters as the gold standard of population projection, but not everyone agrees with its estimates. A population clock on the U.S. Population Reference Bureau’s Web site, spinning faster than numbers on a gas pump, says humans blew past 7 billion weeks ago, reproducing at 25,000 about every 10 seconds.
Wolfgang Lutz, founding director of the Wittgenstein Centre for Demography and Human Capital, challenged the United Nations’ fertility estimates. The International Institute for Applied System Analysis, which collaborates with Lutz’s group, projected that the population won’t reach 7 billion until July next year at the earliest, or January 2013 at the latest.
“We’re constantly challenged, on a daily basis,” Heilig said. “I get between 10 and 15 questions or concerns, people wanting to know something. We try to follow up whatever people complain about. That’s why we do it [recalculate population projections] every second year.”
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