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There are now 7 billion people on the planet, according to the United Nations, and this is much more of a blessing than a curse. While more people means more mouths to feed, it also means more minds to solve humanity's problems. If the world's economy becomes more integrated, and if our policies do more to limit the collateral damage that we do, the promise of more population will dramatically overwhelm the risks.
Everything we eat or drink or drive draws both on the physical gifts of our planet and on human ingenuity. While more people may tax the physical resources of the world - both directly, by consuming more from farms and coal mines, and inadvertently, by generating more greenhouse gases - they only increase the stock of human knowledge. Ideas don't get eroded by use.
Meanwhile, long-held fears of shortages of food and other commodities may be overblown. More than two centuries ago, Thomas Malthus famously wrote that "population, when unchecked, increases in a geometrical ratio," but "subsistence increases only in an arithmetical ratio" and therefore "the poor consequently must live much worse, and many of them be reduced to severe distress." He argued that overpopulation would bring starvation by overwhelming the world's agricultural resources.
His dire predictions helped give economics its reputation as the "dismal science," but Malthus overestimated population growth and underestimated the growth of agricultural productivity. The population of wealthy countries now grows slowly, if at all, and the world's population growth overall has declined from over 2 percent a year in the early 1960s to slightly above 1 percent today.
Productivity on farms has been rising faster. Since 1948, American farm output, according to the US Department of Agriculture, has increased at 1.6 percent per year, despite using far less land for agriculture. In the developing world, the Green Revolution has been even more spectacular, with productivity increases over 3 percent per year between 1960 and 1980 and over 2 percent between 1980 and 2000. The food that now feeds the world is produced by insights - from innovators like Norman Borlaug, the Nobel Prize-winning agricultural scientist who died in 2009 - more than by soil.
It's always a mistake to look at current consumption and supply and predict when we'll run out. Markets, for food and energy and most other products, have a self-regulating character that tends to limit widespread shortages. If extra people demand more food, prices will rise, consumers buy less, and farmers plant more. Far before we run out of gas, prices will soar, consumption will plummet, and companies will find more energy.
Clearly, the outlook is less rosy in poorer, more isolated countries, where famine, not obesity, endangers life. Sub-Saharan Africa can suffer enormously from agricultural shortfalls, especially if climate change causes droughts and deterioration in soil quality. Yet productivity will improve elsewhere. Countries that are part of the global trading system will be relatively safe, because they'll be able to buy wheat from Siberia or Canada, but graver risks face countries that rely only on local food.
The risk that added population poses to the poorest fifth of the planet's people is all the more reason why we should help them move out of rural poverty - and help them grow into urbanized societies that are integrated into the global economy.
The move from farm to city is a transformation from an economy dominated by land, which gets more congested as the population grows, to an economy dominated by ideas, which multiply with density. In knowledge-based economies, every extra human gives us another potential teacher or friend or employer.
The greatest reason to worry about the 7 billion is the inadvertent harm done by humanity. Unfortunately, no market force will automatically counteract the risks caused by massive increases in carbon emissions. We can certainly have 7 billion humans, living in prosperity, with little increase in greenhouse gases, but we need better policies, like a carbon tax, that limit the environmental harm from each new person.
If we control humanity's inadvertent damage, we can fully rejoice in each new person, who will enjoy the wonders of life and contribute to the river of human knowledge that sustains our species.