For details of the New Statesman's Young Music Critic competition, click here.

One summer's day a dozen years ago, while lecturing a class of Spanish graduates on arts criticism, I suddenly realised they hadn't a clue what I was talking about. Spain had lived under Church repression into the 20th century, and under Fascism until General Franco's death in 1975. The notion of a free press was fairly recent and non-partisan arts comment was novel, in a country where art was provided by the government. Criticism, one student said, might be construed as ingratitude.

Tearing up my notes, I spent the next three hours on my feet explaining the history and practices of criticism - from Swift and Addison in the coffee houses of London to the telegenic interpretations of Kenneth Clark, Robert Hughes and Marcel Reich-Ranicki, whose expert enthusiasms developed the critical faculties of an armchair audience: an unexpected democratisation, marvellous to behold and infinitely valuable.

Clark made it possible for a chap in a pub to appreciate Francis Bacon, and Reich-Ranicki for a hausfrau to persuade her neighbour in the butcher's queue that Günter Grass was a more important writer than Hermann Hesse. Kenneth Tynan and Pauline Kael added repertoire tips and quality control to their remit. Their successors attempt to mediate between a bewildered public and the debate about conceptual art. The role of the critic is in constant evolution, a work in progress, a creative necessity.

Yet, in 2010, the critic is an endangered species, almost a write-off. The onslaught of the internet on newspaper economics has ravaged arts journalism. Across the United States, from Miami to Seattle, newspapers have slashed budgets and sacked critics, leaving the New York Times, which is similarly under siege, wielding an unhealthy near-hegemony.

In Britain, the Telegraph and the Times cut review fees to £40 and £60, a disincentive for all but the utterly desperate and the academically tenured (who else would write all night for the price of a cheap pair of shoes?). The mechanism for succession has gone to rust. The average age of classical music reviewers on the nationals is over 55; theatre critics are not much younger. Atrophy is setting in.

At the former incarnation of the Evening Standard eight years ago, I published four to five reviews a night, and six to seven at weekends. No newspaper, the Standard included, maintains that level of engagement today, and as a result much of London's glorious diversity goes unreviewed. Ethnic and experimental arts are ignored, as are venues off the beaten track. When did you last read about a concert in Croydon, Blackheath or Basingstoke? The Brighton Festival is covered, if at all, by local writers because the nationals won't pay train fares.

In the Midlands and the north, most newspapers have gone downmarket. Vasily Petrenko of the Royal Liverpool Philharmonic, an orchestra in the ascendant, asked me not long ago if the Arts Council couldn't subsidise the press to publish reviews. His proposal was not altogether quixotic. A lack of regional reviews distorts relative merit and turns the allocation of state funding into a political lottery. Goodness, as Mae West said in another context, has nothing to do with it.

On television, the BBC has replaced genre authorities with comedians such as Rolf Harris or the gardener Alan Titchmarsh. Alan Yentob, a time-serving executive famed for his creative indecision, has planted himself uncertainly in a main-channel slot. ITV, the Simon Cowell channel, has abolished The South Bank Show. Channel 4 flickers to deceive. Talent shows, dance excepted, are judged by ignorance. TV has abdicated its role in the arts conversation.

These depredations leave criticism in a crisis that is as insoluble as it is universal. Only in France and Germany are critics protected and respected as before, and even in those rule-bound societies the howling of wolves can be heard at the editorial door. If Le Monde hits the wall, there will be no Molière review with le petit déjeuner.

The critics, it is claimed, are authors of their own misfortune, having failed to move with the fast-changing times. Many still cling to the ivory tower. In a court date coming up in Cleveland, Ohio, the music critic Donald Rosenberg is challenging his demotion on the Plain Dealer after prolonged hostility with the music director of the Cleveland Orchestra, Franz Welser-Möst. Many colleagues see this as a test case of critical independence, a good man sacked for his opinions. But in a city wasted by recession, making an issue of a critic's job security looks like angels dancing on a pinhead.

The pulpit tone of old-school critics sounds wrong in an age of instant response. The Guardian's critic Lyn Gardner is aware that many who sit beside her at the theatre can create a Twitter storm before she composes a sentence. Today's critic, she says, needs to be "part of a widening conversation that includes artists and audiences".

Where that takes place is online, and off-media. In Atlanta, Georgia, critics laid off by the local paper cover the city on the portal ArtsCriticATL.com. In London, three dozen writers have sunk their savings into theartsdesk.com. Its founder, the ex-Telegraph dance critic Ismene Brown, argues that the arts cannot survive without "the impassioned debate that springs up in the immediate aftermath of a new production or show". She would like readers to respond to the reviews, but few are taking her up on this so far.

Easy to navigate and chaired by the former Barbican chief John Tusa, theartsdesk.com has 2,000 readers a day and expects four times as many by the end of the year. Aimed at anyone with an urgent going-out need, the site offers quick and useful consumer guidance. But the ground it covers is the central metropolitan agenda dictated by the national press. It adds little by way of diversity, grass roots, regional spread, or international perspective.

For the offbeat stuff you have to go to sites such as electricsheepmagazine.co.uk. Run by a print magazine, Electric Sheep, it reviews fringe and art-house films that seldom get space in the broadsheet newspapers. The writing is confident and well-informed and the scope encompasses everywhere from Spain to South Korea. I was excited to read about a Mexican new-wave gem, I'm Gonna Explode (also reviewed in the NS by Ryan Gilbey) and to catch up on the latest film noir. Unlike mainstream film sites such as rottentomatoes.com, electricsheepmagazine.co.uk avoids industry chit-chat and cheap abuse. It writes about film for people who like film: a classic approach.

Every art form now has a niche website. There's ballet.co.uk and theatremonkey.com, artforum.com and classical.net, to name but one for each sector. Some are sleek as a Gucci shop window, others nerdish and introspective. Often, the reader has no idea whether the critic can be trusted. One record-review loudmouth is an estate agent by day. He may well be no less committed to truth and beauty than a biblical calligrapher, but it is hard to avoid the suspicion that, without roots in the critical tradition, web reviewers are blowing with whatever wind offers the best freebies.

Instead of an organised transition from print to web, what we have is a primordial chaos in which readers hardly know whom to believe. If an overpaid presenter, a Jonathan Ross, raves about a film on the telly, what assurance do we have that he wrote the words and, indeed, holds these views for longer than it takes to mouth them off the autocue?

Nor is the print press in much better shape. The Times has recently replaced its veteran theatre critic, Benedict Nightingale, with a celebrity columnist (Libby Purves) and filled its film slot with a general features writer. The critical incubator has thus been decommissioned and trust in criticism has fallen to an all-time low, lower even than the Irish poet Brendan Behan's glib dismissal: "Critics are like eunuchs in a harem; they know how it's done, they've seen it done every day, but they're unable to do it themselves."

But the world needs good critics more now than ever before if it is not to be given a frontal lobotomy by multinational blandness. Cities without critics will vanish off the cultural radar at the very recessional moment when what they most need is to spark a creative impulse. Nations without critics will fall into the demagogic grip of profiteers such as Cowell and the book-club queen Amanda Ross - unlicensed entertainers whose chief concern is the cheap laugh. For Ross, all books are just books. For a writer, each book is a world unto itself. Without critics to engage with the unknown, those worlds will be lost and the collective intelligence impoverished.

The unholy alliance of Andrew Lloyd Webber and the BBC in the Pop Idol-style casting of low-risk theatrical revivals is a glimpse, a peek through the poisoned keyhole, into what a future without critics might resemble. That future is drawing ever closer.

How can we rescue criticism from the brink of extinction? Some of the best minds in the arts are turning over that question without, at present, much by way of a solution. My feeling is that we have to start from small beginnings, training a new generation of critics in the traditional method and hoping that they will show the resourcefulness to achieve continuity. The New Statesman's search for a young music critic will be widely supported - and not only in this country, as the arts are a global business, but one that, unlike the banks, will never be too big to fail.

The critic of tomorrow will probably tweet a first review in the interval and submit a voice file from the top deck of the homeward-bound bus. The tempo has quickened and the technology has got slicker, but the imperative of bearing independent witness to the arts is unchanged. When the last critic signs off, it will be curtains for civilisation.

Norman Lebrecht, a Whitbread-winning novelist, was assistant editor of the London Evening Standard from 2002 to 2009. His next book, "Why Mahler?", will be published by Faber & Faber in July.