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Outside magazine, September 1999

What's the maximum number of people the Earth can hold?

A. Ciancaglini, Denver, Colorado

We won't even begin to pretend there's a simple answer to this whopper of a question. Population projection is such a wildly unpredictable—and inherently political—conundrum that it's impossible to pin down an exact number. But that hasn't stopped some dauntless demographers from using computer modeling to variously estimate our planet's maximum occupancy, or "carrying capacity," to be between 7.7 billion and 12 billion people. World population in this century has exploded from 1.6 billion in 1900 to nearly six billion (the United Nations estimates we'll reach that number somewhere around this October 12). If present growth continues, we should easily hit this "no vacancy" ceiling within the next century. But before you settle into a deep Malthusian funk, consider a bright spot: 44 percent of the world's inhabitants now live in countries (such as Cuba and Thailand) where fertility is below replacement level. Even so, you don't have to be a deep-ecology alarmist to wonder: Is there enough soil, water, and air to keep 12 billion human hearts alive and beating? Population doomsayers and shrill Cassandras—who warn of a coming "demographic winter" marked by famines and epidemics—have been wrong before, and there are many optimists who still have faith that science and technology can provide the means to avert environmental catastrophe while keeping everyone fed. Maintaining a universally decent standard of living, however, is another story altogether, and some argue we've already exceeded carrying capacity without even realizing it.


Say I'm out sailing on the open ocean, and there's a boat on the horizon. Under ideal circumstances, how far am I seeing with my naked eye?

Curry Haley, Houston, Texas

Although visibility on the high seas is rarely optimal, thanks to the atmosphere's consistently high humidity and the salty particulate matter ceaselessly churned up in ocean spray, it is still usually possible to see all the way to the curvature of the earth—which, for a six-foot-tall person standing at sea level, is only about three miles away. If this sounds astonishingly close, bear in mind this basic principle: When it comes to the earth's curvature, altitude is everything. The higher you are, the more extended the horizon. Shinny 30 feet up your mast, and you'll extend your range to seven miles; jump overboard, and your visual range will shrink to less than a mile. The height of the distant boat is equally important: A hulking oil tanker will ride high above the horizon, visible from perhaps 20 miles away—long before it mows you down.


How big can a hailstone get?

C. Martin, Santa Fe, New Mexico

Disturbingly, outlandishly, and lethally big. Hailstones—such as the softball-size ones that killed 250 people and some 1,600 sheep and goats in India in 1888—are born deep inside the gusty turbulence of cumulonimbus clouds. Powerful updrafts suck raindrops as high as 11 miles into the sky, quickly turning them into ice crystals, which yo-yo up and down, accumulating layers of ice before hurtling to the ground once they become heavy enough. According to the National Oceanic and Atmospheric Administration, the most humongous hailstone on record is a 1.75-pound, basketball-size bomb that fell near the home of Dan White in Coffeyville, Kansas, in September 1970. "I saw this green cloud coming, and I said, 'We're going to get some hail!'" recalls White, noting that NOAA meteorologists made a plaster cast of the spiky orb—now displayed at the Dalton Defenders Museum in downtown Coffeyville. "My boys went out with buckets to hunt for hailstones. It's a good thing they were wearing their football helmets; otherwise they would've been knocked lulu!"


Does the full Moon really get animals riled up, or is that an old wives' tale?

Agatha Robinson, South Bend, Indiana

Our only natural satellite does exert a certain influence on us earthlings, though it doesn't necessarily drive us crazy, as the ancients clearly believed (the word lunatic, remember, comes from the Latin luna, "moon"). Since the Moon's gravitational pull governs ocean tides, it's not surprising that it also governs the reproductive cycles of marine creatures such as tropical sea urchins, fiddler crabs, and grunions. Dive the Great Barrier Reef at the full Moon and you'll witness millions of coral polyps simultaneously releasing clouds of sperm and eggs in a kind of maritime mass orgy—timed to coincide with the month's highest tide. Terrestrial animals (werewolves excluded) may seem more active, too, but that's because full-Moon nights afford better vision for foraging, hunting, and mating. As for humans, in 1985 Nicholas Sanduleak, an astronomer at Case Western Reserve University, reviewed statistics on Cleveland homicides over 11 years—as well as those from similar national studies—and found no scientific correlation between the phases of the Moon and human dementia. Blame it on the goofy drama of horror movies, but if there's any connection, it's probably just psychological.

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