Who should you trust?

It is a simple fact that the world is a complex place. You can't be everywhere and know everything from first-hand experience. And so inevitably you have to accept reports from others about how the world is, and incorporate those reports into your understanding of the world.

But how do you decide whose reports are trustworthy and whose are not? And how do you justify those choices when (also on the basis of second-hand information) others have chosen to trust different people and have come to radically different ideas about the world.

In his comments on Paula Kirby - Believers in denial world. JonJ has quite clearly come to a very different understanding of climate change and its causes from my own conclusions. Neither of us is in a position to do much in the way of verifying the data directly, so both of us are relying on reports from others.

But it is clear that we have chosen to trust a radically different group of people.

So let's have a think about trust and skepticism, who we place our trust in and why.

First, there are some people and some aspects of what they relate which you are able to check directly. So you can develop a view informed by direct evidence as to their trustworthiness and how much weight you can place on their word.

Second, it is possible to make some assessment of a person's character by comparing him or her to others who you know, and in that way make a rough estimate of their trustworthiness even though you have had no opportunity to make any kind of direct check.

Third, you can go by reputation. In assessing somebody's trustworthiness you can rely on the opinion of others who you do trust.

Fourth, you can look at motivation, whether a person has any particular reason to lie on a particular subject, whether they have something to gain by doing so.

Then you can consider, if somebody was lying to you on a topic, whether it is likely that the lie would have been found out by somebody else and word of this reached you.

None of these methods are certain, none are as good as finding out for yourself, but they do allow you to make some kind of assessment of the balance of probability that you are being told the truth.

Let's consider how this might be applied in a case where (if you are not a professional biologist) you are definitely going to have to rely on second-hand knowledge. Let us think about the "debate" between those who accept the evidence for Darwinian evolution, and those who are Young Earth Creationists.

Now, there is a huge amount of scientific evidence in favour of an earth whose age is 4 billion years or so. I shan't go into the details of what it is, that isn't the topic of this post. But if earth is less than 10,000 years old as the Young Earth Creationists would have us believe, then all this scientific evidence must be wrong.

If this is the case, then one and only one of the following three things must be true.

1. Scientists are being entirely honest, but have misinterpreted the data or have yet to discover some decisive bit of evidence which will prove the earth is only a few thousand years old.
2. Scientists are engaged in a world-wide conspiracy to hoodwink us all into thinking the earth is old.
3. The evidence for an old earth is real, but has been put there by God to give the impression of an old earth, and God has done such a good job of it that there is no way for us to be able to see the join.

You'll note that these three options are mutually contradictory. Either the evidence for a young earth exists or it doesn't. If it does, then (3) can't be true. If the evidence does exist, then scientists are being honest about it or they aren't, which means that both (1) and (2) can't simultaneously be true. Creationists don't choose just one of these and stick to it, they slip and slide and slither between these three positions depending on who they are arguing with and what bit of awkward evidence they are trying to explain away.

Let's take option (3) first. This is an unfalsifiable proposition, deliberately designed so that no evidence can possibly be obtained that would decide the question in either direction. It is a variant of the 5 minute hypothesis, and as such can be dismissed. While there is no means of proving it to be false, equally there is no reason to think it is true. The fact that creationists make such retreats into untestable propositions when the going gets tough is a very good reason to consider them untrustworthy.

Let's look next at the idea of the global scientific conspiracy. From what we know of human psychology, it is quite clear that this secret is just too big to keep. If there were such a conspiracy, it would have come out by now. Any scientist who could prove Darwin wrong would have fame that lived down the ages. Too much of a temptation for such a secret to have been kept among so many scientists for so long. It would never have lasted. So the conspiracy idea just isn't plausible.

Lastly, let's look at the idea that the scientists are honest but mistaken. For this to be true, dozens of entirely independent bits of evidence which all point the same way would all have simultaneously to be wrong. Radioactive dating techniques would have to be wrong, geological evidence, continental drift, astronomical and cosmological evidence, physics, biology. All would have to be giving wrong answers, and moreover, entirely by chance all be giving the same wrong answer. This isn't plausible either.

So even if you don't understand all that much about evolution, you can safely trust the word of the scientists on this one. The earth is billions of years old, time enough for Darwinian evolution to have done its work. Darwin was right, though there are always more details to be learned about it.

So lets look next at the issue of man-made climate change, about which JonJ and I had our disagreement. First of all, I will accept that the evidence for man-made climate change is not as strong as the evidence for an earth that is billions of years old. But it is still pretty strong. And it is possible to make an assessment using the same principles. We can still consider a number of possible hypotheses as to how the present situation might have been reached even through man-made climate change doesn't exist.

1. The scientific consensus is mistaken, and although the evidence for man-made climate change appears to be strong, it is in fact being honestly misinterpreted. Either climate change isn't happening, or it has other predominant causes unrelated to human activities.
   
2. There is a worldwide conspiracy of scientists to hoodwink the world into thinking that climate change is man-made when it isn't.

Again, note that the two options are mutually contradictory. A scientist can be dishonest, or can be honestly mistaken, but he can't be both at the same time. you have to choose between the two options.

Let's consider the conspiracy theory first. For this to be true, it would have to be a big secret. Again, too big to last. Peer review is part of the scientific culture, and the discovery of scientific hoaxes such as Piltdown Man is part of scientific folklore. It is not impossible for individual scientists to be dishonest, but the scientific method, with its peer review, repeatability of experiments and cross-checking of different methods against each other is in effect a vast exercise in institutional mistrust designed specifically to ensure that such dishonesty (as well as more mundane mistakes and errors) are brought to light eventually. I've described a bit of the scientific method in a previous article The conflict between science and religion.

Scientists know this, and so the motivation to deceive mostly isn't there, not least because of the near-certainty of being found out eventually. So, broadly speaking, we can rule out a scientific conspiracy as a plausible option.

But what about Climategate? Well, I've read a selection of the emails, and they don't form evidence of a conspiracy. What I have noticed is the following

• It is perfectly clear that those who have released the emails have been very selective about what they have released, and have deliberately chosen the ones which are potentially most damaging. This is called cherry-picking, highlighting the evidence that best supports your case and hiding the rest. It is unscientific and dishonest, and should be taken as a sign of dishonesty on the part of the hackers.
• Much of what is in the emails concerns techniques for understanding the data. For instance, tree-ring data offers a good proxy for temperature, except in the last hundred years or so. We know that it is a good proxy in older times because there is a good correlation between that and direct human temperature measurements. But in the last hundred years, tree rings in industrialised counties are thinner than one would expect. This is likely to be caused by industrial pollution. It can't be caused by lower temperatures, because we can measure the temperature directly and we know what it has been these last hundred years. So the "decline" in temperatures as supposedly indicated by the tree ring data has to be discarded, because we know it is wrong.
• Scientists are human and intemperate just like the rest of us. Few of us would look all that good if the entire contents of our private emails were suddenly and without warning made public. The UEA scientists are learning the hard way something I've known for a while. If you write something down, even in private, you have to be prepared to defend it in public.
• It is necessary for scientists to discuss incomplete, provisional and ongoing work amongst themselves. The unpublished material needs to be gathered together into published papers, where the necessary calculations have been checked, the data has been peer-reviewed and the conclusions justified. Scientific papers are published in such a way that other scientist can replicate the work and see if they obtain the same results. To treat informal unpublished material as if it is a scientific paper and then claim it is incomplete is unreasonable.

So, while Climategate might be evidence that some scientists don't much like each other (an all too human trait), it is not sufficient to justify a belief in a conspiracy theory.

So what about the idea that the scientific consensus is honestly held but wrong? It isn't impossible that this is the case, though it seems unlikely. What uncertainty remains is not about whether we are changing the climate, but rather how fast and by how much we are doing so. The only way to resolve that uncertainty is to do more science and get better answers.

But in the meantime, we need to go with the best guess that the evidence suggests. Our best guess is probably better than a second-best guess that ignores the balance of the evidence. And our best guess suggests that we need to take action now. That will be as much of a discomfort to scientists as the rest of us. In fact, it is worse for scientists - nobody likes to be the bearer of bad news. The scientists would have much preferred to be able to say there is nothing to worry about - they could stop worrying as well.