As the age of cheap oil comes to a close, it's springtime for gloomy futurists. Visions of a brutish world marked by violent squabbles over dwindling reserves, of junkyards littered with abandoned cars, of suburban slums overrun by weeds, of the collapse of industrial agriculture--none of this sounds as outlandish as it once did. Still, most of these horror stories are likely overstated: Energy experts tend to agree that, with a little ingenuity and a generous helping of political will, we could transition away from fossil fuels without being forced to give up our modern lifestyles.

But there's one big exception--an area where a post-carbon world really could mean a radical shift in the way we live. That's the world of commercial flight.

Early signs of an aviation apocalypse are already upon us. As oil prices flirt with $130 per barrel and the dollar struggles, airlines are paying nearly 80 percent more for fuel than they did a year ago. Twenty-five airlines have gone belly-up this year--three to four times the usual yearly rate. Major carriers like American, Northwest, and United, still reeling from the industry downturn after September 11, go barely a month without announcing layoffs and capacity cuts.

And it gets worse from there. Despite recent fluctuations, a growing number of economists are bracing for oil to hit or surpass $200 per barrel in a few years, and most industry analysts agree with Douglas Runte, of RBS Greenwich Capital, who told The Wall Street Journal in June, "Many airline business models cease to work at $135-a-barrel oil prices." After all, most airlines barely figured out how to be profitable in a world of low fuel costs. Jeff Rubin, chief economist of Canadian investment bank CIBC World Markets, has predicted that gasoline will hit $7 per gallon by 2010, forcing some 10 million cars in the United States off the road. If that happens, he told me, "You're going to see an even bigger exit in the airline industry."

As if one plague wasn't enough, the threat of climate change could mean further doom for airlines. In Great Britain, green groups are lobbying hard in favor of aviation fuel taxes and against a proposed third runway at Heathrow Airport, wewhile activist groups, like one called Plane Stupid, have taken to unfurling banners from atop Westminster Palace and elsewhere with slogans like WE FLY, WE DIE. They argue that, at a time when greenhouse gases are pushing global temperature to perilous levels, flying--one of the most energy-intensive forms of travel around--is a luxury the planet simply can't afford. (While aviation currently accounts for just 3 percent of man-made carbondioxide emissions, it's one of the fastest-growing sources, and the true climate impact of flight is around 2.7 times that of carbon dioxide alone, thanks to the added warming effects of nitrogen-oxide emissions and jet contrails.)

As a result of this advocacy, a social stigma against flying is slowly spreading across Europe. While air travel isn't covered by the Kyoto Protocol, the next round of climate-treaty talks will likely address the issue, and the EU has recently announced that it will bring aviation into its emissions-trading regime--forcing airlines to pay for 15 percent of their carbon use starting in 2012. "That's the real deal," says Bill Swelbar, a research engineer at MIT's International Center for Air Transportation. "When you look at some of the taxes and fees being discussed in Europe, we might as well bankrupt our industry today." John Whitelegg, a transportation expert at York University's Stockholm Environment Institute, estimates that requiring airlines to pay the full environmental costs of flight could raise fares as much as five-fold.

Few of the analysts I interviewed wanted to venture predictions about aviation's end of days. One far-reaching scenario, however, was put forward by Anthony Perl and Richard Gilbert, two Canadian transportation experts who, in their new book Transport Revolutions, envision a world in which rising oil prices have reduced domestic flying in the United States roughly 40 percent by 2025--even assuming that airlines improve fuel efficiency by about 50 percent. In such a scenario, the United States could go from having nearly 400 primary airports down to 50 or so; instead of dozens of flights each day between New York and San Francisco carrying 200 people apiece, there might be only a handful carrying 800 or more in new extra-jumbo jets.

The Federal Aviation Administration, for its part, remains bullish on flight, predicting that U.S. airlines will carry 1.3 billion passengers by 2025, nearly double the current number. But even the FAA is starting to soften its outlook, since, already this year, fares in the United States have risen nearly 15 percent on average and some 2.7 million fewer people are expected to fly this summer than last. American Airlines has announced a 12 percent cut in domestic capacity for the rest of the year; United Airlines, a 16 percent cut. Regional jets--smaller planes carrying fewer than 50 passengers that account for one-fourth of all flights today--are being grounded en masse. In the short term, cuts may prove healthy for many airlines, letting them scale back to profitable core markets. But, if oil prices do soar past $200 per barrel, major carriers could start downsizing sharply, abandoning more routes and smaller hubs, and even going out of business for good.

Maybe the gloomy futurists have a point after all, and mass aviation could be coming to an end. No longer would air travel be like the Internet or television--a cheap technology available to virtually anyone, shaping our world in countless little ways. If that happened, the result would mean more than just the end of easy weekend jaunts to Bermuda or annual Christmas visits home. It could mean major shifts in the economy, changes in immigration patterns across the world, and perhaps even a remapping of the planet as we know it.

In the 1950s, flying was a special event: You could hardly find a ticket from New York to Europe for less than $5,000; men put on suits, women wore hats and heels, and some of the luxury planes, like Pan Am's Clipper, had bridal suites, dining salons, and beds. But, in the late '70s, under pressure from consumer groups and business interests, Congress deregulated the industry, allowing upstarts to open up new routes more easily and compete on price, ushering in the modern age of mass aviation. Between 1975 and 2005, inflation-adjusted airfares in the United States plunged some 40 percent, while the annual number of passengers more than tripled. A similar shift swept across the Europe in the '90s, as deregulation gave rise to popular "no-frills" carriers like Ryanair and Easyjet. By 2001, The Atlantic Monthly was envisioning a dawning age of "air taxis"--small planes that would make flight as quotidian as hailing a cab.