A really good guest post is to be found at Anthony Watt’s blog at present which really goes to the heart of my own argument about AGW. I post an extract below bit please take the time to read the full piece:
I drafted this article on November 19th, 2010. At about ten that morning the weather channel, which gets its data for Lethbridge, Alberta from environment Canada and thus ultimately from sensors less than ten kilometers from my house, said the temperature was -17C. At that same time, however, the sensors about four feet above my roof reported a temperature of -19.2C.
By coincidence, and again according to the weather channel, the all time record low for November here, -35.6C, was set on that same day in 1921.
The source number for that claim, presumably 32.08F, is actually an interpolation from various agricultural research and military facilities across southern Alberta, because the airport weather station has been moved a few times and many of the source records lost – but it should be obvious in any case that neither the thermometers in use at airports in 1921 nor the processes in place to record temperature supported anything like that level of precision.
So how cold was it here before I left that morning? there’s really no way to know – and how did that compare to 1921? I don’t know that either.
What I do know is that the values shown were averages taken over time; that neither instrument is predictably accurate to even one decimal place; and that the air between the two is of variable depth, variable humidity, in constant motion, and had markedly less than one chance in twenty-two of being at a real average temperature of -18.1C at about 10 AM that day.
So how does this extrapolate to sticking a thermometer into the troposphere to estimate our planet’s near ground air temperature? Well, in total the world has less than one sensor for every sixty thousand square kilometers; about three quarters of them are closely grouped in the United States, western Europe, and the militarily significant part of southeastern Russia; almost none have trustworthy time-of-readings records for more than a few years; most of the records are both short and discontinuous; most of the readings are accurate only within loose bounds; and an unknown proportion of the time series supposedly formed from instrument readings contain unknown interpolations.
There are other sources of information. For example, weather satellites have produced records for perhaps half the earth’s surface since about the mid seventies – but those records too have unknown source errors; may now contain accumulated and largely undocumented differences from the source data; show significant coverage bias favoring areas important to civil aeronautics; and are generally accessible only in the form of time series whose values are derived from real measurements pertaining mainly to the upper troposphere through calculations calibrated against the same ground sensor readings they’re used to extend and correct.
In contrast many of the proxy records are both long and internally consistent – but they don’t help because these are very coarse grained: whether they’re based on isotope decay or tree rings, the best “rulers” these produce are location specific and marked in decadal or century intervals, not globally applicable and marked in seasons or years.
The bottom line on this is simple: I can’t pretend to know the temperature within a few kilometers of my house right now to within a couple of degrees C without making basic scientific errors in everything from measurement and imagined precision to application – and when people like Jones and Hansen announce in all apparent seriousness that the entire earth is now 0.5C degrees warmer than it was during the period from 1961 to 1990 they’re asking us to accept a very precise number on the basis of data that’s much worse than mine and in the face of applicability, measurement, and computational ambiguities that are orders of magnitude greater.
The credulous have accepted the notion of human agency in “Climate Change” for entirely political reasons and to that end they have been acting in an entirely religious and dogmatic manner. Frankly I would love to hear their explanation of just how they can reconcile the clear problem with the basic data that Paul Murphy outlines in his piece with the certainty that they exhibit about what is clearly little more than a handful of unsupportable claims about the climate from all of their Profits* of doom.