Dr Williams often speaks out on environmental issues
God will not intervene to prevent humanity from wreaking disastrous damage to the environment, the Archbishop of Canterbury has warned.
In a lecture, Dr Rowan Williams urged a "radical change of heart" to prevent runaway climate change.
At York Minster he said humanity should turn away from the selfishness and greed that leads it to ignore its interdependence with the natural world.
And God would not guarantee a "happy ending", he warned.
Dr Williams has often spoken out about environmental issues.
Speaking on Wednesday he said just as God gave humans free will to do "immeasurable damage" to themselves as individuals it seemed "clear" they had the same "terrible freedom" as a human race.
Robert Pigott, religious affairs correspondent
Along with his dramatic urging for people to achieve a personal "conversion" in their attitude to the environment, Archbishop Williams is using the opportunity to teach a slightly more sophisticated take on what Christianity says about the issue.
The concept of a loving and forgiving God has always been central to Christian teaching, even if some traditionalist evangelicals do anticipate the approach of a world-ending apocalypse.
Dr Williams is reluctant to allow Christians to use their faith in a benevolent God - or their fatalism about an apocalypse - to opt out of personal responsibility for the planet Earth.
His key message was about free will - the idea God exercises no control over what people choose to do.
He has used the economic recession to ask fundamental questions about what constitutes genuine wealth and wellbeing, and to argue material consumption has not brought true happiness.
Dr Williams evidently sees the potential for similar lessons to emerge even from the looming crisis over climate change.
"I think that to suggest that God might intervene to protect us from the corporate folly of our practices is as unchristian and unbiblical as to suggest that he protects us from the results of our individual folly or sin," he said.
"God's faithfulness stands, assuring us that even in the most appalling disaster love will not let us go - but it will not be a safety net that guarantees a happy ending in this world."
Without a change of heart, Dr Williams warned, the world faced a number of "doomsday scenarios" including the "ultimate tragedy" of humanity gradually "choked, drowned, or starved by its own stupidity."
The poorest and most vulnerable and our children and grandchildren would pay the heaviest price for climate change, he added.
A Greenpeace spokesman welcomed the speech: "Hundreds of thousands of people are dying every year because we haven't taken the necessary steps to stop climate change.
"Whilst there's nothing wrong in hoping for a miracle, relying on one does seem to be more than a bit reckless.
"We need to all do what we can now, or we're giving up on this world."
Friends of the Earth's executive director, Andy Atkins said: "Humans are responsible for escalating climate change. We have a choice as to how we respond, but we and future generations will live with the consequences of this generation's choice."
Meanwhile, a spokesman for the British Humanist Association said: "The fact that god is not going to help us handle climate change will come as no surprise to many.
"But nor will the reinterpretation of ancient texts to be about stewardship rather than dominion, or indeed any faith in some non-human support.
"What may help us to manage it is human reason and the application of technology, and a recognition that we are on our own on this earth and must handle our own problems."