"I stop at the edge of the pond, see the reflection of trees and sky erased by the wind. And in the sudden void where my future self once stood – a choice, thrown back at me like an echo across the water: What will I do with the time I'm given?

"My sheer belatedness in reaching this point is mind bending – in fact it's perhaps the most difficult thing for me to understand and accept. How could I have gone so long in denial? Not denial of the science, the fact of climate change – I was always reasonably well informed. I mean denial, on some deeper level, of my own part in it, my responsibility – personal and political – and of what climate change will mean in the years to come.

"I took no comfort in knowing that I was far from alone in my lateness. My entire generation, more or less, as we entered middle age, stood indicted. Those of us born in the late sixties and early seventies came of age along with the knowledge of global warming. And yet, a full twenty years on, here we were, the vast majority of us, having done little or nothing about it.

"I, for one, couldn't be bothered – I had a digital revolution to win. I had degrees to earn, a career to build, a family to start. I had places to go, websites to launch. I had bands to see, blogs to read. I had endless cable TV dramas to watch. I had drugs to take, coffee to grind, weight to lose. I had memoirs to write. For Christ's sake, I had my navel to observe. You could say I navel gazed while the planet burned.

"What I'm trying to say here, what I believe needs to be said, is that what I experienced that day at Stone's Pond – the fear, the anguish, the palpable sense of an existential reckoning, all breaking to the surface – was a symptom of something far larger than my own private struggle. What I'm saying is, there's a spiritual crisis, or struggle, at the heart of the climate crisis and the climate struggle – a crisis we've hardly begun to come to grips with, or even acknowledge. The immense suffering that is now inevitable, within this century, on this rapidly warming planet is the result not only of an 'environmental' or 'economic' or 'political' crisis – or even, for that matter, a 'moral' one. It's all of these combined, and yet, if possible, more. It's what I can only call spiritual.

"By 'spiritual' I don't necessarily mean religious (although often it is). I mean deeply human – I mean our deepest, most profound, and ultimately inexpressible sense of ourselves. And by 'crisis' I mean a deep crisis of identity unlike any, perhaps, since Darwin, or Hiroshima – an unnerving sense that, despite all our science and technology, we don't really know who we are and where we're going, or what it means to be alive as a human being at this moment on Earth. A sense that we don't yet know the full magnitude of what we've done to the planet and to future generations, beginning with our own children. A paralyzing sense that we're heading into the unknown, into a new, uncharted wilderness for which we're not prepared. And I want to say that it's our society's failure, our failure, on the whole, to acknowledge and address this essentially spiritual dimension of our global crisis, humanity's greatest, that explains our failure to come to grips with it, morally as well as politically.

"What I'm talking about transcends 'environmentalism.' It transcends religion. It transcends politics and ideology. What I'm talking about is the overriding fact of our shared human predicament. And what I want to suggest is that it requires something of us beyond the usual politics and proposals, the usual answers, the usual pieties. It requires a kind of searching, a kind of questioning, that can move us from self-absorption, isolation, cynicism – from the moral and emotional detachment of denial – to a new kind of engagement.

"Or maybe a very old kind.

"I don't know what it was, exactly – some voice on the wind? – but standing there at Stone's Pond, something drew me back to Walden and Thoreau. I'd gotten to know my surrounding physical landscape, but I was lost when it came to the moral one, and Thoreau is that interior landscape's most prominent local feature – the height looming over my shoulder. Hadn't he written about the moral crises of his time, slavery and war and industrialization, in the grip of a passionate personal engagement with nature? How could I have managed to ignore him? He'd lived just up the road, our local saint, walked the same ground. It was as though I'd been living at the foot of Whitney or Washington – or Katahdin – and never thought to climb it.

"And so I decided, as ridiculous on some level as it might sound, that the first thing I'd do was go back to Thoreau – and I would walk back to Walden. Only this time, I'd pay more attention – I'd find new routes. I'd look for the other Walden, Thoreau's Walden. I had to see if it could still be found. Not the place itself, but the state of mind. And not a refuge or sanctuary, but a way of living in the world, of engaging it, as it is, right now. That's what I had to find – that and the answer to the only question now that mattered, the question Thoreau had asked himself and all of us: 'What will we do with the time we're given?' "