Every age has its economic lunacies, behaviour that points to a wider problem. It might be the rocketing cost of rare tulip bulbs in old Amsterdam, the Spanish practices of the print unions at their mightiest in old Fleet Street or the madness of the junk bond market a few years later. Today there are plenty to choose from, including the booming sales of cars that can do 180mph when congestion reduces traffic to a crawl; or a housing market that has garages and beach huts selling for more than most people dream of.
But if you want something so weird that, when you stop to consider it, it may well make the historians of tomorrow blanch, it is the current craze for popping over to New York to do the shopping. With the pound now close to two dollars, almost every newspaper has been advertising the delights of heading for the airport with a couple of empty suitcases. From jeans to sneakers, digital cameras to handbags, cleansing balm to CDs, who could resist the lures of Macy's, Bloomingdales or New York's branches of Virgin, Apple and Gap?
Well, the short answer is: most people can, or have to, resist it. Either they cannot afford the air tickets or time in the first place, or else the very thought of the queuing, scanning, seat-jammed experience of air travel makes them feel violently sick. It is only a minority who will get the seats, make it to the terminals at Manchester, Glasgow or wherever, and return, in time for Christmas, with their booty.
Yet this is a minority that still has the cultural force with it. Shopping is our favourite leisure activity - most media are basically advertising adjuncts of the shopping industry - and air travel is still the fastest growing mode of transport. According to the Aviation Environment Federation, UK passenger numbers have increased by 310% in 25 years, and the government forecasts that in 14 years the annual number of passengers using British airports will double to 400 million. By that time Boeing expects twice as many aircraft to be in service - a world commercial fleet of 31,750.
The flying craze, it seems, is undiminished by warnings about global warming. According to the travel information company OAG, transatlantic air travel for October had risen 6% in a year, and is at its highest level since 9/11.
I make no apology for adding more raw numbers to this mix, because they are astonishing. World airlines scheduled more than 25,000 flights in October between America and western Europe, an increase of nearly 1,400 in 12 months. This is only a fraction of the world scene, which stood in October at 2.4m flights (a cool 70,000 increase on October 2005), representing more than 280m seats. The biggest increase - 17% - comes from low-cost carriers, and it is the Middle East, India and China that are responsible for the largest growth. So air travel mirrors the wider global economy: the Atlantic, which used to be the most important route, is shrivelling.
Yet, as with global warming generally, we can only hope to change what it is within our reach, which means transatlantic business. In his report for the Treasury, Rod Eddington says that even if passengers are made to pay the full environmental cost of flights, demand in the UK will still outstrip supply. The British economy is abnormally dependent on air travel, particularly in the south-east, so he argues for concentrating expansion of flights on the business-users' hub airports, such as Heathrow. This may make economic sense but its implications for shopping-trip air travel are obvious: it has to stop.
This will not be popular. Put the shopping mania and the flying mania together and you get what has become glamour for the middle classes, if not quite the masses. Once hopping over to America for the weekend was the kind of thing you read about Hollywood legends or City tycoons doing; now it's available to most people on a salary, if they want it badly enough. We shouldn't be snobbish: flying to shop is not intrinsically worse than flying to see old buildings. But it is environmentally suicidal. Mad. Bonkers.
Yet it is a madness that feeds on itself. A different segment of the air travel market makes the point eloquently. Apparently the pre-Christmas alpine skiing season is in trouble for the obvious reason - lack of snow. Races have been cancelled from France to Norway. Here is yet another small piece of the mountain of evidence about global warming, to which the air travel mania so notably contributes. And what is our reaction? Apparently it is to head for North America - I mean fly there, of course - where the snow is still plentiful and the skiing top notch.
We know it's not sustainable. Yet millions of us, probably most of us, are terrible hypocrites. We want to do something about global warming. The thought of those sparkling glaciers disappearing into history is terrible. But this year, at any rate, the skiing break matters more. Who knows how often the chance will come? Let's not linger. The same goes for shopping and the weak dollar (caused in part by the awesome overhang of US debt, another symptom of the consumer economy running riot). This is not sustainable but it's here, now, so let's grab those suitcases and head to the airport.
What we need, most obviously, is a much tougher and more realistic form of political leadership than we have had so far, and a stronger civic culture that opposes the shopping mania of today's media. We need to be obliged to change our habits - and that is going to require a level of courage not obvious from Westminster, or from anywhere else.
All political parties say they "get it" when it comes to cheap air travel, but don't hold your breath for any significant moves to cut it. This week's autumn statement may well see a gesture in this direction, but we can expect any tax rises to be modest, not punitive. Which politician, after all, is going to want to stand accused of being a killjoy, of spoiling the voters' holidays?
Yet in the end, for the sake of the environment we will just have to move around the world less. We will have to do our shopping nearer at hand, not further away. We have to do business remotely, as the internet once promised, and not casually nip across an ocean. Look beyond Christmas: cold turkey's on the menu.
Jackie Ashley