The best information on what is going to happen is in the scientific consensus.

The people whose opinion about what burning fossile fuels (and deforestation, and the construction of cement) will do to the future of the climate is to be found in the scientific consensus.

This is not to say that the scientific consensus is correct or that it should not be questioned. In fact, one of the reasons to trust the scientific consensus is that it is produced by an institution that very much respects the possibility of error and the value of challenging current ideas against new evidence. There is no science scripture that says, "You must believe this and those who do not are to be sentenced to death as heretics." Science is filled with examples of people challenging received opinion and, eventually, winning.

Still, science is done by scientists, and scientists are human beings. In any community of, say, 20,000 human beings you are going to have some who are paradigms of virtue and some who lack virtue. You will find people engaged in politics and fraud, corrupted by their own biases, acting on petty grievances against one another and seeking to do favors for their friends.

Science, as an institution, does not deny the fallibility of scientists. In fact, the institution of science is built on the fact that scientists cannot always be trusted and safeguards must be put in place to lessen the harm done by human failings.

With all of its flaws, there is still no better source of information than the scientific consensus. Worst of all, again, are those people who claim that they can visit a half-dozen web pages on the internet and call themselves an expert capable of second-guessing a community of tens of thousands of researchers who have spent their lives studying the relevant subject matters.

If, however, that's not the case, and nobody else is willing to defend the idea of "scientific consensus", then there seems to be little point in my trying to hold back the tide of opinion on this forum

let me tell you a story. It's 1991, I am flying home from Germany, sitting next to a man who is almost in tears, he is so upset. He's a physician involved in an FDA study of a new drug. It's a double-blind study involving four separate teams---one plans the study, another administers the drug to patients, a third assesses the effect on patients, and a fourth analyzes results. The teams do not know each other, and are prohibited from personal contact of any sort, on peril of contaminating the results. This man had been sitting in the Frankfurt airport, innocently chatting with another man, when they discovered to their mutual horror they are on two different teams studying the same drug. They were required to report their encounter to the FDA. And my companion was now waiting to see if the FDA would declare their multi-year, multi-million dollar study invalid because of this chance contact.

For a person with a medical background, accustomed to this degree of rigor in research, the protocols of climate science appear considerably more relaxed. In climate science, it's permissible for raw data to be "touched," or modified, by many hands. Gaps in temperature and proxy records are filled in. Suspect values are deleted because a scientist deems them erroneous. A researcher may elect to use parts of existing records, ignoring other parts. But the fact that the data has been modified in so many ways inevitably raises the question of whether the results of a given study are wholly or partially caused by the modifications themselves.

In saying this, I am not casting aspersions on the motives or fair-mindedness of climate scientists. Rather, what is at issue is whether the methodology of climate science is sufficiently rigorous to yield a reliable result. At the very least we should want the reassurance of independent verification by another lab, in which they make their own decisions about how to handle the data, and yet arrive at a similar result.

Because any study where a single team plans the research, carries it out, supervises the analysis, and writes their own final report, carries a very high risk of undetected bias. That risk, for example, would automatically preclude the validity of the results of a similarly structured study that tested the efficacy of a drug.

By the same token, any verification of the study by investigators with whom the researcher had a professional relationship — people with whom, for example, he had published papers in the past, would not be accepted. That's peer review by pals, and it's unavoidably biased. Yet these issues are central to the now-familiar story of the "Hockeystick graph" and the debate surrounding it.

To summarize it briefly: in 1998-99 the American climate researcher Michael Mann and his co-workers published an estimate of global temperatures from the year 1000 to 1980. Mann's results appeared to show a spike in recent temperatures that was unprecedented in the last thousand years. His alarming report formed the centerpiece of the U.N.'s Third Assessment Report, in 2001.

Mann's work was immediately criticized because it didn't show the well-known Medieval Warm Period, when temperatures were warmer than they are today, or the Little Ice Age that began around 1500, when the climate was colder than today. But real fireworks began when two Canadian researchers, McIntyre and McKitrick, attempted to replicate Mann's study. They found grave errors in the work, which they detailed in 2003: calculation errors, data used twice, data filled in, and a computer program that generated a hockeystick out of any data fed to it — even random data. Mann's work has since been dismissed by scientists around the world who subscribe to global warning.

Why did the UN accept Mann's report so uncritically? Why didn't they catch the errors? Because the IPCC doesn't do independent verification. And perhaps because Mann himself was in charge of the section of the report that included his work.