If you've ever seen large-scale deforestation, especially of the rainforest, and seen it close up when it's just happened, you feel you're in the aftermath of an armoured battle. The scale of the destruction stuns you: cleared ground which seems to be everywhere smoking, burning tree stumps flickering like huge candles. It feels as if some giant beast has torn off a great lump of the landscape and savagely consumed it, leaving bits of it bleeding behind.
Serious deforestation has been going on for more than 30 years across the world's tropical zones, starting in Amazonia and gathering speed, spreading to Indonesia and then to West Africa.
The effect has been staggering: rainforests, which provide us with so much, from oxygen production to carbon storage, once covered 14 per cent of the earth's surface; now, they cover about 6 per cent, and the devastation is continuing.
This is something that the Green Movement, despite immense effort and a certain amount of progress, has not been able to stop. If we examine the 50 years of the Green Movement's existence and try to tot up its failures, the inability to halt deforestation would probably be near the top of the list.
We might bracket it with a similar calamity, this one taking place in the world's oceans: overfishing, and the parallel inability, despite great exertions, to bring it under control.
Why have green activists had such success in limiting pollution, but not in curbing overfishing and deforestation? The answer is that pollution is in essence a tactical environmental issue, something that can be dealt with on its own, while the other two are strategic, meaning they are part of the very structure of things.
So pollution can be brought right down by operating your company differently, and the only reason companies did not do that in the first place was either laziness or miserliness: truly bad publicity will always make them change.
But deforestation and overfishing are something else entirely, part of the human exploitation of natural resources. The pressure for these processes to continue is ultimately driven by rising demand, which is in turn caused by the rise in human numbers – or to put it another way, by the ever-expanding scale of the human enterprise.
Although public attitudes have been changed by the Green Movement, arguably the biggest failure of all during its first 50 years has been not to change those attitudes profoundly enough.
The former director of Friends of the Earth Tony Juniper says the problem is fundamentally about culture.
"We work to take on these environmental challenges without having any kind of profound connection with nature. We've lost it talking in a mechanistic, policy-oriented way.
"We've tried to make it all about numbers, parts per million, complicated policy instruments, and as a result we've lost something that's essential. Most people couldn't tell you the names of country flowers by the side of the road, the birds that are singing. It's a disconnect in our world view – a failure in our philosophy."
Changing culture is much harder than changing what comes out of a pipe. It's a recognition that the next 50 years of the environment movement may not offer the clear-cut, achievable victories of its first half-century.