Last week the government published a shortlist of five schemes for harnessing the tidal power of the river Severn, to provide renewable electricity. It is no secret which is favoured in Whitehall - the biggest one, as ever: a 10-mile mega-barrage that would cost £14bn, and could generate 5% of Britain's power.
This may sound the kind of thing environmentalists ought to be unanimously keen on. Yet many say that the damage done by this mammoth piece of technology - destroying mudflats and bird habitats, and weakening the famous tidal wave known as the Severn bore - would outweigh the benefits. A battle is being joined over the fate of Britain's longest river, and it is highlighting an uncomfortable truth which environmentalists don't much like dwelling on: some green technologies can have distinctly un-green impacts.
Britain is a small, overcrowded and overdeveloped country in which wild places are at a premium. On moors and glens, on tidal rivers and empty beaches, humanity's impact can be escaped, at least for a time. A mountain is an example of what the American poet Robinson Jeffers called "the transhuman magnificence": a place that rises above the detritus of civilisation, where we may go to experience the reality of nature and the reality of ourselves. I have had such experiences on mountains, and they helped lead me to become an environmentalist.
When I climb a mountain, then, and find that the detritus of civilisation has followed me, in the form of giant wind turbines, my reaction is not to jump for joy because it is zero-carbon detritus. My reaction is to wonder how anyone could miss the point so spectacularly. And when I hear other environmentalists responding to my concerns with aggressive dismissal - particularly if they have never visited the mountain in question - I get really quite depressed.
Fifteen or so years ago, as an excitable young road protester, I tried to prevent the destruction of beautiful places. To me, building a motorway through ancient downland, or a bypass through a watermeadow, was a desecration. To me today, a windfarm on a mountain is a similar desecration. A tidal barrage that turns a great river into a glorified mill stream is a desecration. Carpeting the Sahara with giant solar panels would be a desecration. The motivation may be different, but the destruction of the wild and the wonderful is the same.
It is de rigueur among greens to respond to such heresy by explaining that we have less than 100 months to get to grips with global warming; a few turbines on the odd hillside is a small price for preventing the apocalypse that would result from our failure.
Well, maybe. But while renewable energy is a good thing in principle, if schemes end up, like their conventional forbears, as centralised mega-projects that override local feeling and destroy wild landscapes, then they become precisely the kind of projects that people like me cut their teeth trying to stop.
If you don't understand what makes Helvellyn awe-inspiring, or the Severn bore magnificent, or the Lewis peat moors evocative, in some deep - and possibly inexplicable - sense, then you will have no idea what I'm talking about. These places will seem not to be places at all, but "resources", ripe for exploitation; and your response to them will be about not breathing space or spiritual nourishment, but kilowatt hours and energy security.
Environmentalism is surely inspired by a sense of wonder at the richness of the natural world. Without that inspiration, it becomes the kind of bleached, technocratic, office-bound variety so common today, which pushes for the taming of rivers, mountains and wildlands in the name of making the ever-expanding human economy more "sustainable". Desperate to seem grown up, serious and economically literate, many greens seem to have become terrified of talking about the things that motivated them in the first place. Beauty. Wildness. A connection to the non-human, the remote, the untamed.
Human impact on the world is now so enormous that the civilisation we have built is feeling the shudders. If the world's governments, with the collusion of some environmentalists, want to pretend that the need to question that civilisation's values can be staved off with wave machines and wind turbines, it is up to them. But we should understand that, whether we dig up coal or carpet the wildlands with barrages and turbines, we are making a statement: this is our world, and we will exploit every inch of it. We want - no, need - more energy for our TVs, cars and planes. It is our right. There is no alternative.
There is only one place this attitude can lead: to a collision between civilisation and the biosphere. I don't see any number of barrages doing much to prevent that. And I would put a lot of money on the winner.