When the fourth assessment report of the Intergovernmental Panel on Climate Change was released recently, the media and the IPCC functionaries concentrated on the point that part of the known increase in global mean temperatures in the past century or so is due to human activities. Quite so, although we did not need elaborate computer models - or intense scientific debate - to work that out, as this article will show.
The other side to all the recent screaming, however, and one that the environment industry which includes the IPCC is not keen to emphasise, is that part of the increase is due to natural climate cycles. That was the real change.
In previous years the IPCC has tried to blame all the warming on human activity, and was recently severely embarrassed in those efforts. The panel has never acknowledged this embarrassment and, tellingly, has never been seriously questioned over it, although the more recent report shows signs of preferring to keep within known science, rather than include last minute scare stories about ice caps melting and the like. This is welcome.
In one sense all of this does not matter very much. If human activities are changing the climate then something should be done, no matter what the degree of change. This article does not address the issue of emissions, nor does it deny climate change (nor is the author in the pay of oil companies, which is a shame). Instead we will look at the issue of whether the IPCC predictions mean anything or whether they are of any use at all.
As is now well known, climate changes naturally. There are very large variations into and out of ice ages, which scientists seem to know something about, although there is still a lot of debate about the mechanisms involved. But there are also small scale changes over a few decades or a century or two which remain very mysterious.
In the most recent of those minor changes, it is known that up until about 1860 the world was in the grip of what has been called The Little Ice Age. The colder weather has been confirmed by everything from ice cores to surveys of cloud cover in Renaissance paintings (see Little Ice Age, Brian Fagan, Basic Books, 2000 - Fagan is a professor of Archaeology at the University of California). That Little Ice Age, in turn, had several sub variations of somewhat warmer and somewhat colder climate.
Scientists know that changes in solar activity have some hand in all this, but we can only guess at the interaction between the sun, the atmosphere, the ice caps, clouds, oceans currents, aerosols, water vapour, carbon dioxide (natural and man made), dust from volcanoes and heaven knows what else besides. The oceans, in particular, are proving vastly more complicated than scientists suspected until just a few years ago.
Scientists know that in 1860 average temperatures were low, so that at least some part of the 1C plus increase since then must be natural. They also believe that the upswing might have something to do with a general increase in solar activity.
However, the warming trend has gone on too long. There is no previous, recent period where warming has continued for as long as it has up to now (as far as anyone knows). Ergo, human activity might (90 per cent likely) be to blame, and never mind the battalions of IPCC scientists meeting in endless committees.
The Little Ice Age book cited above gave that figure as accepted when it was published. The really tricky part is working out how much of the warming is natural and how much is artificial.
The IPCC, for its part, has fought bitterly against the suggestion that part of the warming may be natural with most of the fight being over a thing called the hockey stick graph - a piece of analysis done mainly by Michael Mann, a climatologist at the University of Virginia.
Distilled from readings of various ice cores and tree rings and the like, the graph showed temperatures rising exponentially and neatly in line with the rise of industrial activity. Perfect!