Joseph Nicholas, Tottenham, London

I've been noodling from time to time at the on-line version of Challenger 21. Indeed, I've saved parts of it to my hard drive, so that I can read it without running up the phone bill. (In the UK, all calls are charged according to their length. Surfing the internet on dial-up can therefore be a bit expensive.) In this case - when I've had the opportunity to read some more, I'll probably write some more - I'm responding to some of the comments in the letter column; from (in order) Joseph Major, Martin Morse Wooster and Hank Reinhardt.

"People who are in horror movies don't watch horror movies," says Joseph Major. He's forgetting Scream, the first and the best of the series (in fact, it was made as a stand-alone, with no thought that there might be sequels), in which the characters comment explicitly on the tropes and conventions of the teen slasher genre and their likely default roles in the "real version" being played out around them. (If I recall correctly, I think that one point one of the characters addresses the others on videotape, saying that if his friends are watching this then he obviously didn't survive.)

My favorite line in that movie came when a character named infamous mass murderers - "Jack the Ripper ... Charles Manson ... O.J.!"

"Where did Benford get the notion that we will run out of oil in 50 years?" asks Martin Morse Wooster, and continues: "All the evidence of the past suggests that when the price of oil rises, companies get to work and find new areas to drill in. Isn't it true that if we only had the proven reserves of 1978, we'd have very little oil now?" Unfortunately, Wooster is here confusing total reserves, recoverable reserves and economically recoverable reserves. I shall attempt to elucidate.

When the Club of Rome published The Limits To Growth in 1970, predicting an imminent end to exploitable resources of raw materials and fossil fuels, it was basing its predictions on economically recoverable reserves, as the economics of extraction then stood. That is, it recognised that there were recoverable reserves over and above those it classified as economically recoverable, but considered that the cost of extracting those additional reserves would exceed the revenue to be gained from them.

What has happened in the thirty years since is that extractive technologies have continued to develop, to the point where what would have been economically unrecoverable in 1970 can now be exploited for profit. This has occurred independently of increases in the actual price of oil - apart from the artificial shortages and price hikes of 1973 (and the taxes levied on fuel at the pump by governments), the relative cost of oil has remained largely unchanged. Unfortunately, the focus on price -- an obvious headline indicator, and one that is much more meaningful to the public at large - has tended to mask developments in extractive technology, leading to the belief that the discovery of new (i.e., undetected or suspected) reserves is dependent on the price going up.

What has actually happened, however, is that the proportion of total reserves classified as economically recoverable has increased markedly - while known total reserves have increased very little. In other words, we're finally beginning to push up against the limits. Which is where the Association for the Study of Peak Oil, to which I referred in my previous letter, comes in.

"In my seventy years I have read many editorials and comments espousing all sorts of positions," begins Hank Reinhardt's letter. " Some have been superb, some have been lousy, but I am hard pressed to find one to compare with Guy's latest editorial. It is beyond compare! It is magnificent! Never have I encountered one piece that is so filled with ignorance, hypocrisy, absurd exaggeration and just pure drivel."

After that my brain glazed over a bit - it's a long rant, and as usual with long rants from Hank Reinhardt, the actual subject matter tends to disappear beneath the torrent of bile he pours forth. And, to be honest, I don't think you answered him very well.

Step back from the actual subject matter - the invasion of Iraq, Abu Ghraib, Saddam Hussein's torturers, Waco and Ruby Ridge - and look at the basic point he's arguing. "It's all right for us to do this, because others do it too." In other words, that two wrongs really do make a right. Once that is grasped, his whole argument falls over, and there's no need to worry either about his details of who did what to whom when in history or the question of whether this sort of behaviour does or does not run counter to what the US allegedly stands for, because his moral standpoint has vanished - or probably never existed in the first place.

Mind you, I enjoyed his argument about the Vietnam War being a Democratic war because the Democrats were in power at the time. Therefore, because he doesn't like Democrats, it was an evil and unjust war. Whereas the invasion of Iraq, because it was mounted by a Republican government, is therefore perfectly acceptable. (Or something like that. As I say, his actual points tend to be submerged by his invective.) As he himself might say: it is beyond compare! Magnificent! And utterly, utterly ridiculous.