At any time in the past 100,000 years, a space traveler approaching the Earth from a million miles away would have made out a blue globe with ice caps on the top and bottom. Some scientists predict that by 2050, the Arctic Ocean will be free of ice during the high summer months of the northern hemisphere. The North Polar ice cap may be gone by the end of the current century, replaced by sunny blue water.
Ernest Hemingway's fabled snows of Kilimanjaro, which existed when Neanderthals met the first humans and later as Ötzi lay dying in the Alps and later yet when the ancient Romans hunted game animals for the Colosseum, may be gone by the time you read this. Glaciers are melting at breakneck pace in the Andes of South America, the Alps of Europe, the Himalaya of South Asia--portending horrendous floods, mud slides, and other disasters of Biblical proportions. Atop the Royal Range in Bolivia, glaciers at altitudes of 17,000 to 18,000 feet including the Chacaltaya, Huayna Potosí, and Condoriri are melting at dozens of feet per year and will vanish soon. This in turn will most likely cause disastrous permanent disruptions in the water supply for drinking, irrigation, farming, and hydroelectric power. It's easy to see the chain of events snowballing--no pun intended--with major impact on human and other living populations. The disruption of habitats may well prove fatal for many large animal species already teetering on the brink of extinction.
The Greenhouse Effect (global warming) causes carbon dioxide and other pollutant emissions to gather--some invisible, some seen as a layer of haze in the troposphere. That's the habitable portion of the atmosphere, which is about 11 miles thick at the equator where the air is warmer, and a little more than half that, 6-8 miles thick, at the poles where the air is colder. As solar radiation pours into the troposphere and reflects off the oceans and continents, a lot of the short-wavelength energy (about a third of the sunshine we receive) can't escape from the atmosphere, so the atmosphere gradually warms. Nobody knows what part is due to natural climate cycles, but it's clear that humans are helping global warming along.
One way the casual observer can see the effect of human activity on the atmosphere is in looking at the night sky. In our growing cities, it is often difficult to make out the constellations of stars because the air is dirty. By contrast, if you stand by a quiet desert road at night far from civilization, you can't make out the constellations either--because the night sky is so black and so clear, and the carpet of stars is so dense, that the constellations are lost there for entirely different reasons--a breathtaking sight most humans will never see as they pursue their urban lives. One astronomer recently estimated that more than two thirds of humans today have never seen the Milky Way sprawling from end to end across the night sky for the same reason.
Global warming...or global icing?
Will your neighborhood become a beach as sea levels rise due to melting ice? Or will the ongoing warming trend kick some switches that will suddenly cause shaggy glacial predators on high snowdrifts to stalk past your living room window?
Whichever way the pendulum swings, global warming is a reality today, and we are seeing violent weather effects--typhoons, floods, snow storms, heat waves--sometimes not even in their proper season. So where will global warming take us? In this article, we'll look at the counterintuitive possibility that we may be heading like an express train right into the next ice age; or, if you prefer, into the rest of an ongoing ice age during which the childhood of human civilization, the Holocene, may have been a brief 12,000 year pause.
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