The political revolution never really came close to happening in 1968. But it is clear now that the cultural revolutions of the 1960s are here to stay. The rights of women, ethnic minorities and gays are enshrined in law and embedded in consciousness.
How do revolutions of this kind come about? Typically, there will be a slow growth of consciousness, then a headline-grabbing series of books and events, and after that a permeation of new ideas and attitudes through the fabric of society. Education and the culture industry play an important role.
Consider feminism. The Second Sex by Simone de Beauvoir was a bestseller when it appeared in English translation in the United States in 1953, but it was not until the very end of the 1960s that the movement gained mass attention - thanks to the coining of the phrase "women's lib", the tabloid myth of mass public bra-burnings, and the publication of Germaine Greer's The Female Eunuch. A decade later, feminism was everywhere: in fiction, drama and film, and across the academic disciplines (with the exception of the hard sciences).
There was a similar progression in the arenas of race and gay rights. But what about the other great cultural revolution of the 1960s: environmental consciousness?
In 1962, Rachel Carson's Silent Spring woke the world up to the dangers of toxic pesticides. In the 1970s, Love Canal and Agent Orange became symbols of the devastating ecological consequences of rampant capitalism and imperialism, while the oil crisis made everyone aware of the limits of natural resources. By the turn of the century, more people were engaged in environ- mental campaigning of various kinds - from local protests over new housing and roads to the global consciousness-raising of Greenpeace - than in any other kind of political direct action.
Yet there has not been a corresponding revolution in cultural practice. We have feminist history, feminist literary theory and feminist anthropology by the barrow-load. Ditto for "post-colonial" studies. There are university departments of women's studies, MAs in sexual dissidence, the Orange Prize for women's fiction, and, in the theatre, Gay Sweatshop and Split Britches. From Salman Rushdie to Zadie Smith, the modern novel has pulsated with visions of multiculturalism. So where are the equivalents for the promotion of an environmental agenda? How often do you get to see a film or play, or read a novel or work of history or cultural commentary, that is manifestly "green"?
My own field of expertise is English literature. Over the past 20 years, just about every major author since Chaucer has been analysed in relation to race and gender. There has been a huge industry in the recovery of the lost voices of the literary past - female poets, black autobiographers, gay novelists. Minorities of all kinds have been honoured, and the literary canon redrawn accordingly. Old liberal humanists in English departments up and down the country have had to recognise that there is no going back to the morally bracing but crampingly provincial "great tradition" of F R Leavis.
I started doing ecological literary criticism a decade ago, when I grew impatient with a tendency among the most advanced readers of William Wordsworth to claim that there is "no such thing as nature". This seemed a counter-intuitive way of looking at someone who took such an interest in the ecology of the Lake District. When I looked around for precedents for my approach, I was greeted with near silence.
As far as I am aware, the first example of self-consciously ecological literary criticism - published just two years after Rachel Carson - was an article called "Enclosures: the ecological significance of a poem by John Clare". Clare, a 19th-century farm labourer, was a proto-ecologist in that he perceived human society and the natural environment to be held together in a complex and delicate web. But Clare has always been on the margin of the literary canon, and the article's appearance in Mother Earth, the journal of the Soil Association, was hardly noticed by academics.
In the 1970s, the growth decade of feminist reading, there was only one (not very good) book of ecological literary criticism. There was just one more in the 1980s when, following the publication of Edward Said's Orientalism, post-colonial theory came to dominate the agenda. Whatever academic discipline or field of artistic creation you consider, the story is the same.
Why has the greening of culture lagged so far behind the other revolutions? Environmental activists might reply that they are too busy doing things: stopping a road, saving a whale, trampling a GM crop trial. They have no time to bother with theory, with the past or with the arts.
They are wrong. Before you can change policies, you must change attitudes. This is the lesson to be learnt from those other movements. It must sometimes seem curious that passionate feminists devote their time to writing articles and teaching seminars about Shakespeare's misogyny and the patriarchalism of Renaissance culture, rather than campaigning against low pay for women or female circumcision in Africa. But these feminists know that, by reading the past, they can influence the future. Their project has been so successful that everyone is now alert to the woman question. So, too, with racial awareness.
By the same token, a green rereading of history - and literary history and philosophy and every other humanistic field - is a necessary precondition for a deeper understanding of our environmental crisis. "A placeless world is as unthinkable as a bodiless self," writes the American philosopher Edward Casey. All human activity takes place in an environment. Everything we do is influenced by, and influences, our environment.
History is shaped by natural forces, as well as social ones. Climate is as formative as class. Environmental degradation - deforestation in particular - has been the main cause of the end of empires. Environmental history is now one of the fastest-growing fields in the discipline, especially so in India, where the effects of climate on society are much more immediately visible than they are here.
Yet this is a very recent development. The first self-consciously Green History of the World appeared in 1991. Symptomatically, its author was not a professional academic historian, but the "disgraced" former civil servant Clive Ponting.
The obvious reason for the slow growth of "green cultural studies" is that environmentalism does not conform to the model of "identity politics". The most influential feminist theorists and historians have been women. They are themselves the beneficiaries of the revolution they preach. So, too, when the empire writes back: the most influential post-colonial thinkers have been non-whites. The pioneers of "queer theory" are gay. Male feminists, white post-colonialists and heterosexual queer theorists have to tread carefully: can they speak on behalf of the Others whom their ancestors have spent centuries oppressing?
Environmental theorists are not themselves trees or whales or ozone holes. They have no choice but to speak on behalf of the Other (ie, the non-human) that we have so long exploited. We can ask women and non-whites their opinion as to whether a book, a work of art, a historical action or a philosophical assumption is sexist or racist. But before what tribunal can we establish that any of these things might be speciesist?
Environmental ethics is a burgeoning field in philosophy but, like the animal rights movement, it has difficulty with the central premise in ethics, from Aristotle to Kant to Rawls, namely that the flip side of rights is obligation. If a new grouping - the unpropertied, women, slaves - claims rights, it must also sign up for certain duties. How can you extend rights to animals or the environment, when they have no obligations to us? All answers to this question involve the abandonment of the familiar contractual models of justice and ethics.
Ethics, history, belief, artistic creation: they are all part of culture. This is the core of the problem. What is culture? Culture is the opposite of nature. We make ourselves human by setting ourselves against nature. We cannot ever "return to nature" in the manner of Jean-Jacques Rousseau's noble savage. But nature returns to us. As a green reading of Freud might have it, the repressed returns in the form of flood, famine and pollution. This, then, is the troubling paradox: the greening of culture is both a contradiction in terms and a necessity for our very survival on the planet.
Where does culture happen? In the interior realm of the reader's consciousness, in the darkened auditorium of the theatre and cinema, the electronic box of the television, the cyberspace of the web, the climate-controlled research library, the closed atmosphere behind the windows of the university seminar room - screened, in several senses of the word, from the immediacies of nature. Is it any wonder that modern culture, in both its creative and its critical manifestations, has found little place for the smell of earth, the bite of insect and the contamination of air and water?
Two big ideas dominated the humanities in the late 20th century. One was the theory of the social construction of reality. The other was a belief in the primacy of representation. Both proved deeply inimical to any consideration of the relationship between culture and nature. If everything is predetermined by ideology, there can be no unmediated access to nature. Equally, if all artworks and cultural analyses are refracted through the prism of language and other signifying codes, then we can only ever know our representations of nature, not the thing itself.
It is useful to be made aware that, say, an 18th-century landscape painting is shaped by, among other things, a market place for artistic patronage and a set of formal representational techniques influenced by the neoclassicism of Claude Lorrain. Cultural representations of nature are always mediated. It does not follow that nature somehow does not exist. Yet that was the conclusion towards which late 20th-century cultural critics moved. "There is no nature except as it is constituted by acts of political definition made possible by particular forms of government." So said one sophisticated critic of Wordsworth. In one sense, he is right: Wordsworth's Lake District today is, in many respects, physically shaped by the politics of farming, forestry and tourism. But in another sense, he is alarmingly wrong: the planet will still be here after humankind and all its forms of government are obliterated by toxic emission, genetic mutation, nuclear annihilation or whatever. As feminism and multiculturalism made the noble Enlightenment idea of "man" a taboo term in academic discourse, so the theories of representation and social construction placed an embargo on the equally noble Romantic idea of "nature".
Wallace Stevens will, I think, come to be recognised as the most authentic poet of the 20th century. Stevens spent his whole working life insulated from nature in a Connecticut insurance office. Yet read him carefully, and you will find him returning again and again to the complex but necessary reciprocal interplay of mind and world, culture and nature. As he wrote in his poem "The Planet on the Table":
His self and the sun were one
And his poems, although makings of his self,
Were no less makings of the sun.
It was not important that they survive.
What mattered was that they should bear
Some lineament or character,
Some affluence, if only half-perceived,
In the poverty of their words,
Of the planet of which they were part.
We are beginning to recognise that the truly pioneering cultural criticism of the late 20th century was not the postmodern self-indulgence of Parisian gurus such as Derrida and Baudrillard, but a more grounded and varied body of work: Raymond Williams's The Country and the City, Keith Thomas's Man and the Natural World, Robert Pogue Harrison's Forests: the shadow of civilisation, Mike Davis's eco-sociological studies of Los Angeles, City of Quartz and Ecology of Fear. With the turn of the century, ecological history and literary criticism have come of age, thanks to books including John McNeill's Something New Under the Sun: an environmental history of the 20th century and the Harvard scholar Lawrence Buell's Writing for an Endangered World.
Through the 1990s, artists such as Richard Long and Andy Goldsworthy worked with natural materials and made the process of dwelling upon the earth an essential part of their vision. Among the more memorable independent films of the past few years was Todd Haynes's Safe, with Julianne Moore as a woman afflicted with what she becomes convinced are environmentally induced allergic symptoms. And among the handful of truly great novels of our time is Don DeLillo's White Noise, with its "airborne toxic event".
All these works recognise the inseparability of nature and culture. They show that there is no way out of our ecological networks but, at the same time, they recognise that there is no way back to the forest, to unmediated nature. In Haynes's film, the symptoms of Julianne Moore's character might be attributable to traffic, but they might be psychosomatic. In DeLillo, toxic pollution is both a frightening scientific possibility and a forceful metaphor for the inauthenticity of modern culture.
Harrison's eloquent cultural history of the forest begins with a quotation from the 18th-century philosopher Giambattista Vico: "This was the order of human institutions: first the forests, after that the huts, then the villages, next the cities, and finally the academies." It is the academies that have been among the last to wake up to the true extent of our ecological crisis. But at last we are getting there. Wallace Stevens again:
They will get it straight one day at the Sorbonne.
We shall return at twilight from the lecture
Pleased that the irrational is rational,
Until flicked by feeling, in a gildered street,
I call you by name, my green, my fluent mundo.
Jonathan Bate is Leverhulme research professor at Liverpool University and author of The Song of the Earth (Picador)