Forget about the rain; what will the Olympics do for the economy? The circumstances when London was chosen to host the games were of course utterly different from those the country encounters now. That was the height of a boom, while this is at best a disappointingly slow recovery.
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The good news is that at least there is slack in the economy were the Games to provide a significant boost to demand. The bad news is that the record of the Olympics bringing any lasting gain to the host country is discouraging. Right now though, even a short-term boost would be more than welcome.
Some good news first, which is nothing to do with economics. There is a consistent bias towards the host country when it comes to awarding medals, a bias from which you can apparently calculate how many medals the UK will win. If this is right, we become number three in the gold medal table, after the US and China and ahead of Russia, as you can see from the top chart.
But – rather like winning the World Cup or that other great sporting event, the Eurovision Song Contest – topping the charts does not necessarily bring economic success with it. Indeed looking at what happened to Greece, you might think that there is even a reverse effect: a country that spends a lot of money on a sporting party ends up with unused facilities and a load of debt. It took 30 years for Montreal to pay off the debts accumulated for the 1976 Olympics.
Fortunately the debts for the London Olympics will be quite small in relation both to the size of the UK economy and to the rate at which we are running up other debts. The Games are also small in relation to the London economy, a contrast with Athens and Barcelona, but more similar to Beijing and Sydney.
Indeed, the more you crawl over the numbers, the smaller the impact would seem to be.
There are obvious positives in that many people will visit the city who might not have come. Those people will spend money. But visitor numbers have been strong already, with this week Heathrow reporting record throughput for the first half of the year and anecdotally at least, it would seem that some visitors will have put off trips to avoid Olympic congestion. Having special lanes painted on the streets for the high and mighty officials is a most un-London thing.
Besides, economies grow by continuous effort, not one-off events. At a consumption level, money spent now is money not available to be spent later, so any short-term boost to spending will be offset by a decline afterwards. And £10bn or £15bn or whatever the Games eventually cost is not big in relation to an economy of £1,500bn a year.
There have been examples where the publicity of the games, plus the new infrastructure put in for them, has had a lasting impact on the economy. The best example of that has been Barcelona, which had become a destination of choice for the conference business as a result of hosting the Olympics. But even Barcelona is worrying about its still-to-be-repaid debts, and you could argue that the city was in any case due for a revival given its location, architecture and other assets.
London is not in the position of needing to be put on the map: more people pass through its airports than any other place on earth.
The city that perhaps presents the best parallel to London is Sydney. A huge amount of planning went into making sure, as far as possible, that the facilities put in were designed for after-use, and I think that, just as we have learnt a great deal about athletics training from Australia, we have also learnt about matching facilities to long-term needs rather than a short-term show.
However, studies of the economic impact on the Sydney economy have been somewhat discouraging. Ahead of the event they pointed to a sharp increase in economic activity, a boost in fact. After the event, the conclusion was much more sober. Indeed the conclusion was that viewed overall, the Games brought little net benefit to the city. My guess is that, with one exception, in five years' time that will be what we conclude here.
That exception is that we will learn from the exercise in small ways. For example, the pressure on immigration facilities will force us, actually is already forcing us, to think how to use scarce resources more wisely. Segregation of visitors from countries with strong checks at the other end from those with weak checks makes huge sense.
Once we have got rid of the "Zil lanes" (Russian leaders used to be ferried around in huge Zil limousines along special lanes from which other cars were excluded) we may learn something about traffic management. And one bit of London ripe for redevelopment has had a lot of money spent on it.
There is one further point. The Olympics have over the years reflected the changing balance of the world: the decline of the Soviet empire, the rise of China, the continued significance of the US, the rising importance of Latin America and Africa. You can see that, in crude form, in the bottom table, which shows the rising proportion of gold medals won by the emerging world. That was at a record in Beijing, if you exclude the distortions that resulted from the boycott in Moscow, and it will be intriguing to see whether the proportion rises again in London.
And that will surely be the best way to see this Olympics and Paralympics, as a celebration of globalisation. The last one was a celebration of the rise of China. The next one in Rio de Janeiro will be a celebration of the rise of Latin America.
This should not be seen as a celebration of Britain, or at least not mainly that; rather it reflects how one place, London, happens to be just at the moment measurably more international than any place on earth.