When the Guardian launched its Comment is free threads, it was one of the most exciting developments in journalism I had ever witnessed. Suddenly, everyone could play. Columnists and leader writers were no longer the voice of God: they could be immediately challenged, corrected, held to account. People with something to say could say it, expertise from every field and every part of the world was harnessed.

The early discussions were invigorating, fascinating, thrilling. They forced me to smarten up my act, to try to close the gaps in my thinking, to consider the argument more carefully before setting it out. It seemed like an exercise in mutual education: a Frierian teach-in of the kind that I am too young to have experienced, but which always seemed to me to have been the way to go.

There is still something of this in the threads: whenever I have the stomach to read all the way through them I find a few comments which teach me something new, introduce me to interesting stories and links, or force me to challenge and reconsider the things I have said. But such posts increasingly look like gems among dross.

On the Guardian's environment site in particular, and to a lesser extent on threads across the Guardian's output, considered discussion is being drowned in a tide of vituperative gibberish. A few hundred commenters appear to be engaged in a competition to reach the outer limits of stupidity. They post so often and shout so loudly that intelligent debate appears to have fled from many threads, as other posters have simply given up in disgust. I've now reached the point at which I can't be bothered to read beyond the first page or so of comments. It is simply too depressing.

The pattern, where environmental issues are concerned, is always the same. You can raise any issue you like, introduce a dossier of new information, deploy a novel argument, drop a shocking revelation. The comments which follow appear almost to have been pre-written. Whether or not you mentioned it, large numbers will concentrate on climate change – or rather on denying its existence. Another tranche will concentrate on attacking the parentage and lifestyle of the author. Very few address the substance of the article.

I believe that much of this is native idiocy: the infantile blathering of people who have no idea how to engage in debate. Many of the posters appear to have fallen for the nonsense produced by professional climate change deniers, and to have adopted their rhetoric and methods. But it is implausible to suppose that this is all that's going on. As I documented extensively in my book Heat, and as sites like DeSmogBlog and Exxonsecrets show, there is a large and well-funded campaign by oil, coal and electricity companies to insert their views into the media.

They have two main modes of operating: paying people to masquerade as independent experts, and paying people to masquerade as members of the public. These fake "concerned citizens" claim to be worried about a conspiracy by governments and scientists to raise taxes and restrict their freedoms in the name of tackling a non-existent issue. This tactic is called astroturfing. It's a well-trodden technique, also deployed extensively by the tobacco industry. You pay a public relations company to create a fake grassroots (astroturf) movement, composed of people who are paid for their services. They lobby against government attempts to regulate the industry and seek to drown out and discredit people who draw attention to the issues the corporations want the public to ignore.

Considering the lengths to which these companies have gone to insert themselves into publications where there is a risk of exposure, it is inconceivable that they are not making use of the Guardian's threads, where they are protected by the posters' anonymity. Some of the commenters on these threads have been paid to disseminate their nonsense, but we have no means, under the current system, of knowing which ones they are.

Two months ago I read some comments by a person using the moniker scunnered52, whose tone and content reminded me of material published by professional deniers. I called him out, asking "Is my suspicion correct? How about providing a verifiable identity to lay this concern to rest?" I repeated my challenge in another thread. He used distraction and avoidance in his replies, but would not answer or even address my question, which gave me the strong impression that my suspicion was correct.

So what should we do to prevent these threads from becoming the plaything of undisclosed corporate interests? My view is that everyone should be free to say whatever they want. I have never asked for a comment to be removed, nor will I do so. I believe that the threads should be unmoderated, except to protect the Guardian from Britain's ridiculous libel laws. But I also believe that everyone who comments here should be accountable: in other words that the rest of us should be able to see who they are. By hiding behind pseudonyms, commenters here are exposed to no danger of damaging their reputations by spouting nonsense. Astroturfers can adopt any number of identities, perhaps posting under different names in the same thread. We have no idea whether we are reading genuine views or corporate propaganda. There is also an asymmetry here: you know who I am; in fact some people on these threads seem to know more about me than I do. But I have no idea who I am arguing with.

Some people object that verifiable identities could expose posters to the risk of being traced and attacked. This is nonsense. I make no secret of my whereabouts and attract more controversy than almost anyone on these pages, but I have never felt at risk, even when, during the first few months of the Iraq war, I received emails threatening to kill, torture and mutilate me almost every day. For all the huffing and puffing in cyberspace, people simply don't care enough to take it into the real world.

So how could it best be done? Amazon prevents people from reviewing their own work by taking credit card numbers from anyone who wants to post. Is this the right way to go, or is there a better way of doing it? What do you think?

Monbiot.com