Think of humanity as a herd of caribou living on an arctic island with no predators and abundant sustenance. We reproduce wildly until inevitably the sustenance, the energy source, is overtaxed and collapses.

Then we begin to die. In the case of humanity, billions of us.

The analogy and the dark prophecy are Mike Ruppert’s. And he argues it already has begun, this great dying, and there is nothing we can do to stop it.

For the resource that has sustained human civilization for the past hundred or so years, which underpinned the quadrupling of global population and on which our whole industrial civilization is built, is in accelerating and irreversible decline. That resource is fossil fuel, and in particular, oil.

As Mr. Ruppert, a middle-aged former L.A. cop turned journalist and author, details at length in his book, Confronting Collapse, and also in the documentary Collapse, which will open this year’s Martha’s Vineyard Film Festival next week, that decline means a great deal more than finding an alternative to run our internal combustion engines.

Oil is everywhere in our daily lives. In everything plastic. In paint. There are seven gallons in every car tire. We literally eat of fossil fuels, for they are the feedstock of fertilizers.

They are the food of our economic system, too. Hence the subtitle of the book: The Crisis of Energy and Money in a Post Peak Oil World.

Oil production passed its peak of 8.5 million barrels a day in late 2005. And though the bursting of the housing bubble which followed shortly thereafter gets most blame for the great recession, Mr. Ruppert argues the energy crisis underlaid it; it was for oil that America went to war in Iraq, and so built its massive debt.

And the passing of peak oil will ensure the economic crisis never really ends, for any increase in economic activity will simply push up energy prices and thus snuff itself out.

“We have only seen the first leg of it,” he said on Tuesday, speaking from his home in Los Angeles before heading to the Vineyard next week, when he will discuss his ideas and the film at the festival, after its Friday night screening and in a special program Saturday morning.

“New data is showing an accelerating decline in oil production, faster than I said in the movie.

“And just since the movie came out [late last year], about half the predictions in it have already come true,” he said. “I refer to the insolvency of the FDIC [the Federal Deposit Insurance Corporation, intended to shore up U.S. banks], which is now $21 billion in the red, and there are 700 banks now on a danger list, that will probably fail this year, and to the economic crises in Dubai, in Greece,” he said.

“We are having a massive, global debt crisis that’s now involving possible sovereign defaults in Greece, Spain, even Britain.”

He continued to make predictions. The British pound would shortly be “hammered.” The European Union would break down. There would be no recovery in the United States.

Nor would the U.S. be insulated from the humanitarian crisis which will inevitably follow, which will ultimately see the human population of the planet decline by three to five billion, he said.

“It is not possible to continue infinite consumption and infinite population growth on a finite planet,” Mr. Ruppert said. “It is that simple. All bubbles burst, including population bubbles. Maybe five billion people exist on this planet who didn’t exist before we had oil.

“Those people live everywhere, in every country. People here are going to starve and freeze to death as they are doing now in eastern Europe.

“It may hit even worse in some respects here in the United States because our agricultural system and food production is horribly corrupted by fossil fuels, and much of our soil is basically useless without petrochemicals.

“The countries that are less industrialized, less tied into the global economic/financial growth model, will have a better chance. Because their people are farmers now, they’re less reliant on all the products of energy.

“As I sometimes say, if you were going to take a fall, would you rather fall from the penthouse to the gutter, or from the sidewalk to the gutter?”

Surely though, something can be done to avert disaster?

“If you mean, is there something that will allow us to continue living as we have, no,” he said. “There is no solution. None.”

Maybe if President Carter (who wrote to him endorsing the book, Mr. Ruppert said) had not been run out of office 30 years ago “for telling the truth” about energy, something might have been done.

But it takes 30 years to change an energy infrastructure, and trillions of dollars, quantities of time and money not now available. And anyway, most mooted alternatives are inadequate or counterproductive. Ethanol requires more energy to produce than it delivers. Clean coal is an oxymoron, utterly unfeasible. Wind, solar and nuclear power could never be brought online fast enough to prevent industrial and economic collapse. His book analyzes them all at length.

Furthermore it takes will, and Mr. Ruppert says that will is lacking. Indeed, the powers that be, the corporate interests, the big media, national governments, deliberately hide the grim reality.

“The protectors of the old infinite growth, monetary paradigm want to just let four or five billion people die, and recreate themselves and that paradigm. But they will do so on a planet where the resources for growth have been devastated,” he said.

The only hope lies in local organization.

“National governments are really useless at this point. It will depend on how much local communities can organize in terms of food and energy production and essential services.”

So, that’s Mr. Ruppert’s message, in condensed form. To explore it at greater length, read his book. The essence of the movie, however, is something else. It’s at least as much about the messenger as about the message. Whether director Chris Smith is really on board with the whole collapse thesis is never clear.

He seems more about highlighting the loneliness of the zealot — whether the zealot be tragically right or tragically deluded. The movie is essentially 82 minutes of edited interview with Mr. Ruppert as he sits, chain-smoking, in what looks like a bunker or a cell (it was actually the basement of an abandoned meat packing plant in L.A.), his message illustrated with the odd graph, chart and bit of news footage.

This is not a movie like An Inconvenient Truth, in which the filmmaker sets out to persuade the audience to join the crusade for change. Rather, it puts the crusader, Mr. Ruppert in the dock, and invites judgement. Is he a flake? What has been the personal cost of the crusade?

It would have been a very cruel movie, on a human level, if Mr. Ruppert had been revealed as a deluded conspiracy theorist. It would also have been a more comforting one, on a global level.

In the end though, Mr. Ruppert emerges with dignity. Obsessed, for sure, a little extreme at times, but mostly he’s matter-of-fact, very well researched and persuasive.

And definitely a man sadly resigned to the role of Cassandra.

Yet in the interview this week, he presented something else — an incongruous mix of optimism, purposefulness and wry humor.

He’s “joyful, because what I am seeing since the book and since the movie more particularly, is that there are millions of people around the world who are aware of this problem.”

He has received serious coverage, and the reviews of the movie have been overwhelmingly positive.

He said: “We are still fighting to save enough lives that future generations will have a chance to create a resource-based economy that is not predicated on all that stuff that has driven us now to the edge of extinction. That’s the great contest, what parts of human civilization survive.”

He concludes the conversation by saying: “Have a cheery day now.”