A wise old saying

There is an old saying in the law: as the allegation is more serious so should the proof be more clear. I am not going to turn this musing into a paper on burdens and standards of proof, but I do want to look at that saying and see what it means in practice.

There are two different principles at work here. One is that the more unusual the activity complained of the less likely people are to believe that it occurred. For example a witness who says "I was standing at the bus stop outside my house at 8am waiting for the bus to take me to work" is describing something very ordinary and everyday, it takes no leap of faith to accept that he is telling the truth. Were he to say "I was standing on my head on top of the bus shelter waiting for a big pink fairy to carry me to work" even the kindest soul is likely to have some difficulty accepting it as true. It is probably right to say that the commission of a very serious criminal offence is something which does not happen as often as the commission of minor offences. To take an obvious example, there are fewer murders in London each year than there are examples of littering the pavement. An accusation of murder necessarily requires the prosecution to persuade the jury that something very unusual happened and that, of itself, makes the jury less likely to convict the Defendant without clear evidence.

The other principle is that where the penalty for a particular offence is a serious penalty it is fair to expect the offence to be proved very clearly. Not only is murder a rare occurrence, it also carries a mandatory life sentence. It is hardly surprising that juries often take a long time to deliberate in murder cases even where the evidence is very strong indeed, they know the consequences of a guilty verdict and will not cut any corners.

These thought-processes merely reflect standards that have developed over time in our society. We have a well-developed sense of fairness, we know what is serious and what is trivial, we know that it is fair to give serious matters more mature consideration than trivial matters. Perhaps it is better expressed as a negative: we know it would be unfair to convict someone of murder unless the evidence is very clear indeed. Many murders are just ordinary assaults with highly unfortunate results but that does not prevent the jury from requiring overwhelming proof of the assault where the victim died and less powerful proof where exactly the same type of blow merely left the victim bruised.

This reasoning is now coming to the fore in the great global warming debate. When the hoo-hah started some years ago only a small number of people felt a need to examine the theory in any detail because the only threatened consequence was that the planet would get a bit warmer. How nice, we all thought, a longer cricket season, less ice on the roads in winter, lower heating bills, let's have a bit more of it if it's not too much trouble, thank you.

Then the predictions turned to plague, famine and pestilence. That's a rather different scenario. We don't like plague, famine and pestilence, we must stamp out this evil. There was still relatively little interest in the science behind the arguments because there was no price to pay except to cut down a bit on coal and petrol. That's not a problem, I will drive at 60mph rather than 70 in order to prevent starvation in Africa. All that was required was equivalent to not dropping litter, it was no great inconvenience and a lot of good would result.

Over the last three or four years things have changed dramatically. All of a sudden we were told we must stop driving, stop flying, stop this, stop that and we looked at how those changes would affect our lives. Those who hanker for life in a cave with nothing but a small cabbage patch for food and hand chewed raffia clothing could not be happier, their dream is coming to pass. The rest of us face calls for such dramatic changes to our comforts that we ask whether it really is necessary. Suddenly we are threatened with the equivalent of the mandatory life sentence and, not surprisingly, we ask whether the case for such a serious penalty is proved with sufficient clarity. The accepted, perhaps even orthodox, position of the alarmists was accepted without debate when it did not threaten us, then we became a jury.

The task of a scientist when he appears before a jury is to explain the science in handy bite-sized chunks so that it can be understood by those who need to understand it in order to reach a decision. If he is exposed as an obsessive the jury might well be reluctant to accept what he says without supporting evidence. In the global warming debate we find obsessive scientists on both sides, we are bombarded with hyperbole and worst case scenarios. What we want to know, sitting in our jury box, is whether the case of the alarmists is proved. Do they have sufficient evidence to justify the life sentence with which we are now threatened?

I wonder whether, when making their doomsday predictions, they realised they were making their task of persuading us about the science harder rather than easier.