Perhaps the best-known example is the impact that the first oil shock, at the end of 1973 and the beginning of 1974, had on energy consumption. For the previous 100 years the energy efficiency of Western economies had been improving slowly. We used much more energy, of course, but energy use per unit of output had been falling. Power stations in 1970 were much larger than power stations in 1920 but they were also much more efficient. But progress was slow and uneven until the oil shock when, within three or four years, the world made a sudden leap forward. In some areas there has been a bit of back-sliding since then, but the point that the shock reinforced an existing trend still stands.
Now think about beef. The shock is principally a British one, for BSE is unusual elsewhere, and we should not kid ourselves that we are, as a country, important enough to have any great social impact on the rest of the world. Yet the beef crisis reinforces some behavioural changes that are happening here and also taking place in other Western countries. So a question mark over British beef will to some extent make people elsewhere think about the food the West eats, the way it produces it, and the implications for the global food balance.
First, the food we eat: one of the facts that has repeatedly been quoted is that people have been cutting back on beef over the last decade. And not just Britons. With the exception of Japan, where beef consumption is traditionally low, people in all large developed countries are tending to eat less red meat.
Just why this should be is not really clear. You can explain part of it by money: the revolution in poultry farming has cut the price of chicken relative to that of beef or lamb. There are worries about health. There are some not very well co-ordinated concerns about the health effects of eating an excess of red meat. Individual studies seem to show that red meat (and dairy products) is associated with higher incidence of some illnesses such as prostate cancer.
The trend may have something to do with changes in family structure, in particular the rise in single-person households. It may be connected with the tendency for people to snack rather than sit down to a meal. And it may in part be a reflection of wider concerns about the values of a consumer society: even carnivores feel uncomfortable about the way animals are transported and slaughtered.
Will Britons be eating even less meat five years from now? I'm pretty sure they will, for the beef scare is pushing at an open door. People who were cutting back anyway have been given further impetus to do so. And I predict that a similar decline will take place in other developed countries, for all the same forces, with the exception of the BSE scare, are there, too.
But if we will eat less meat, perhaps it will be of better quality and from animals that have been treated with more concern for their welfare. This leads to the second point: the way the West produces its food.
There will, of course, be changes in the way we produce beef. We will see this in the supermarkets: the origin of meat will be more clearly labelled. It is perfectly possible with bar-coding to know from which farm an animal comes. I expect we will have much more product differentiation as meat comes to be sold less as a commodity and more as a specialist product. We will be much more careful what feed is given to animals, changing the way we produce meat and dairy products, because the market will demand it.
While it would be naive to expect the whole factory farming revolution of the last 40 years to be reversed, it is clear that intensive farming methods, for all output, will come under scrutiny. If the feed manufacturers can make an error, what about the producers of fertiliser? In the short term it is perfectly possible to increase grain output by piling more and more fertiliser on the soil, just as it is possible to encourage animals to put on weight more quickly by adjusting their diet. But every time a shock like BSE comes along it makes us question whether there are costs that only become apparent in the very long term.
Consumers are being trained to be sceptical of the assurances of the industry's experts, and if farming, in particular in Europe, remains a protected, producer-dominated industry, ultimately consumers will win. Expect "real food" to become more in demand.
This leads to perhaps the biggest issue of all: what will be the impact of changes in Western agriculture and Western lifestyles on the problem of feeding a rapidly increasing world population? We are up to about 5.7 billion and adding 90 million people a year. Even if the rate of growth falls, it is very hard to see there being less than 8.5 billion people on earth in 2025. Virtually all those people will be in the developing world, leading to the argument that, while it may be possible to feed a larger population, the food will be in the "wrong" places. We know that additional output can be produced in the developed world, but that is not where the additional people will live.
I can see three ways in which this whole argument may change. First, if we eat less meat we put less pressure on the food chain: feeding grain to animals and then eating them is an inefficient way of producing food. We need a bit less than 3,000 calories a day, but because of the meat content, the total calories needed to supply a Western diet are about 15,000. If we ate a Japanese diet with less animal protein we would need perhaps 11,000 calories.
One should not push this argument too far, for there are parts of the world that are very good at producing meat - wet grasslands - but which would be poor land for most grain. But the general fact holds that if we cut back on meat the global food balance improves.
Second, changes in Western agriculture may in the short term make it less efficient: we may produce better quality but, in the short run at least, there may be less of it. So in a way the key to improving the quality of overall output is to eat less meat.
A change in buyer choices will, therefore, balance out a change in farming methods. Broadly speaking, the West remains in balance. There may, however, be a third effect: by redirecting our research so that we farm better but less intensively, we may learn things that are of help to the farmers of the developing world who face the real task of feeding the additional mouths. This is surely important. We know that Western methods are frequently inappropriate for developing countries. Now we are going to have to unlearn some of the methods we have been using. But in doing so we may be able to contribute to the really grinding problem: an extra three billion mouths.
It is hard to find silver linings in the clouds of BSE, but making us recalculate the costs and consequences of excessive factory farming is surely one.