See post below for introduction to this subject.

What has this blog found out so far? Well first of all, global warming is hot hot hot. A huge amount of today’s Times was about climate change. There was a pretty typical article, in this case by Mary Ann Sieghart: “it no longer seems tenable to dismiss the existence of global warming or to deny the contribution that humans have made to it.” What’s changed? the amount of coverage perhaps.

There was also an important letter from Terry Evans on climate change: “Sir, Your leading article (“Green Grind”, March 10 ) demonstrates the problem facing the layman in the debate over the cause of climate change”. He’s right of course, and that’s why this blog is trying to advance from the status of layman to keen amateur. We’ll be returning to Tel’s arguments in the future.

Meanwhile this is what this blog has found so far:

1) For the last 25 years, the earth’s measured temperature has been increasing pretty steadily and over the last century has been rising for most but not all of the time.

2) The theory that mankind has caused this – at least in part – is mainly because of a correlation between CO2 and global temperatures over the last 400,000 years (as proved by antarctic ice-cores). This is the famous Al Gore moment.

3) The current argument promoted by ‘The Great Global Warming Swindle‘ is that this correlation is coincidence rather than causation – because the rise in CO2 comes after the rise in temperature whereas the empirical man might expect cause to precede effect. In general, the consensus defence to this is not that the measurements of antarctic ice-cores are subject to error (and so this blog must assume that they are not), but that the flow of cause and effect is complicated in this case by feedback loops, threshholds, other gases and other possibilities.
As Terry Evans says “The discovery that deep ice cores showed that, in the past, carbon dioxide followed the movement of temperature means that serious positive feedback processes come into play which will increase carbon dioxide concentrations as air temperatures rise — ie, possible runaway warming. Most of these feedback processes are well understood.” This means that initial warming is caused by solar activity or suchlike, but is then sustained and possibly increased by rising CO2 levels (probably from warmer oceans retaining less dissolved gas).

4) Sceptics on the other hand believe that as global temperatures increase, so CO2 levels increase (probably from warmer oceans retaining less dissolved gas) but that the change in CO2 levels in no serious way explains previous or current changes in temperature. Changes in temperature are to do with the sun alone or its position relative to the earth – or possibly to the increase in methane emissions by the elephants who support this diskworld.

5) This blog was disappointed to learn (probably erroneously as it was from Wikipedia) that greenhouse gases do not warm the earth in the same way as a greenhouse warms. It had assumed that all controversy could be sorted out by getting a greenhouse, putting a small model of the earth inside it and chucking some dry ice into the bucket on the floor.

6) Hang on in there – we’re about to get to the point.

7) What is clear to this blog is that the relationship between CO2 levels and temperature is much more complicated than the layman is normally allowed to imagine. Catch a look at this graph:
Look at that sharp verticle red line right on the right of the graph – thats the CO2 level in the atmosphere – everyone agrees that this increase (150 years out of 400,000) is due to human activity (let’s be specific – its due to your gas-guzzling SUV, Mr America – now bow your head in shame). The question is – why aren’t we frying tonight?
CO2 levels now stand at 0.0365%, but in the past, the peak levels of around 0.028% occurred when the average global temperature was about 1.5C higher than the latest 5 year average.

8) Look, however much it wants to, this blog is unwilling to call this a load of old horseshit until it understands more about the feedback argument. But in its younger days, this blog used to make a living in the area of econometric modelling – things like the relationship between price and sales – in that case, whether cause or effect follow each other is much less important: a decrease in price could coincide with a competitive product launch and not cause an immediate increase in sales but over time and on average, the lower price increases the desirability of the product. In the CO2/temparature relationship, this blog doesn’t yet understand why that relationship shouldn’t be immediate – and waits for your comments.

9) When it was still involved in the black arts of modelling, this blog would have said that the relationship between CO2 and temparature had recently broken down, or fundamentally changed in ways that cannot currently be predicted (and cut its fees accordingly).
Because the website that I took the last graph from: also had this graph: to show the latest cause and effect
but if that is the current relationship, then the 400000 year plot – highly simplified – would look something like this:
which is not quite the same sort of Al Gore moment.

Dear me, tomorrow we’ll go back to something interesting like the number of potato sellers on the M4.