It's called "The Most Terrifying Video You'll Ever See" and while it's not a horror movie, it is rather disturbing. And it's sweeping the Internet.

The YouTube video is actually a 10-minute lecture on global warming, delivered by Oregon high school science teacher Greg Craven. It may sound preachy, but it's hugely popular and has generated millions of hits on multiple websites.

Craven delivers the low-tech, video treatise from his home in Monmouth, Ore., armed with a black marker and a whiteboard.

He methodically argues that the debate over whether humans caused global warming is moot; instead, Craven says, "the risk of not acting far outweighs the risk of acting."

The film bears plenty of similarities to Al Gore's "An Inconvenient Truth" but Craven argues that Gore didn't go far enough in his film, noting that the way the globe is heading because of climate change will make "Gore look like a sissy Pollyanna with no guts who sugarcoated the bad news."

Craven says at its worst, climate change could bring droughts, famine, floods, dust bowls, economic collapse and the displacement of millions. He concedes that the policy changes that are needed to counter global warming will be economically painful. But he insists that the costs of maintaining the status quo will be worse.

After Craven posted his homemade video on YouTube back in June, it did exactly what he hoped it would do: it went "viral."

Thousands of people clicked on the catchy title then forwarded it on to their friends, until more than 4 million people had viewed it. It now ranks among the most popular videos in YouTube's news and politics category.

Craven told Canada AM that he felt compelled to make the video after he learned how desperate the environmental situation is.

"I knew a lot of the science already, so it just took someone showing me how the puzzle pieces fit together for me to come out with this daunting sense of dread of how things are going to be different," the soft-spoken teacher said.

"This is not just another environmental issue. This may eat our lunch. This is fundamentally different because in a complex system like the climate, there may be tipping points where irreversible damage is done, but you don't see it until it's too late to do something about it. That's what really has motivated me."

Not surprisingly, the video has also generated lots of reaction -- and plenty of it is critical. Craven says he listened to those arguments and then prepared his rebuttal.

"I got 7,000 critical comments. I sorted through those and as a result of those refined my argument and produced 'How It All Ends,' which patches the holes in 'The Most Terrifying Video You'll Ever See'," he says.

"It's a 10-minute video but it's a complex issue."

Craven says "How It All Ends" links to an additional six hours of explanatory videos to bolster his argument. 

"It wasn't supposed to be like that. It sort of exploded on me," he laughs.

In the videos, Craven tries to keep it light by wearing goofy hats and setting chemicals on fire in a lab to demonstrate his points.

Craven says it took him months to produce the 44-part package, so he sent his wife, Jodi, and their two daughters to visit relatives for a week at a time, while he survived on takeout and energy drinks as he produced the videos.

All that intensive work -- and terrible eating -- eventually got to him. He had to visit the emergency room when he began experiencing chest pains. The doctors there told him to reduce his stress level and take it easy.

Craven says he's now feeling much better and has reduced his teaching hours to part-time so he can spend more time with his family. He's also considiring writing a book about all he has learned.