Global warming sure is a tough sell.

Al Gore equates it to this analogy: If a frog jumps into a beaker of boiling water, it will immediately jump out. But if placed in one where the water is room temperature and then heated, the frog will sit there the entire time until it boils to death.

“An Inconvenient Truth” offers a more expanded exploration of this idea, with humans as frogs and global warming as the boiling water.

Because the gradual process is one that doesn’t have the instant impact of, say, ramming airliners into buildings, the public apparently requires years worth of convincing as to the catastrophic threat. Even then, there is no guarantee the situation will be embraced.

Perhaps one film can change that attitude.

Riding a poster blurb that dubs it “the most terrifying movie of the year,” the documentary “An Inconvenient Truth” is so convincing that it makes opposers of the argument as credible as Holocaust deniers.

The former vice president points out how there is “100 percent agreement” within the scientific community. However, the energy industry has tried to obfuscate the argument, employing the same tactics used by the tobacco lobby to reposition global warming as a debate.

Using a comprehensive but easy-to-digest multimedia presentation, Gore explains how the burning of fossil fuels at such a high rate is causing glaciers and snow to melt. (The United States is, not surprisingly, the guiltiest of nations.) Those frozen masses reflect sunlight whereas seawater retains it, so their reduction equals more heat that is unable to escape Earth’s atmosphere. Thus the modern escalation of deadly heat waves, hurricanes, typhoons, carbon dioxide levels, etc., continue to plague the planet.

If nothing is done within the next 10 years, Gore describes the inevitable outcome as “a nature hike through the Book of Revelations.”

It’s hard to argue with the facts introduced in “An Inconvenient Truth” – and since I’m not a big oil tycoon, I don’t have to. But there are some questionable areas when it comes to the filmmaking.

Director Davis Guggenheim shows quite an improvement from his lone previous feature, the 2000 thriller “Gossip.” In my original review of the film I chastised, “Guggenheim tries to inject more than the recommended limit of fancy camerawork, jarring edits and hipster soundtrack singles into his film, and the outrageous art direction is especially eye-popping in its absurdity.”

He must have taken the criticism to heart, because the filmmaker does the exact opposite with this documentary. He relies on a no-frills approach to make his case. Much of the picture is simply Gore delivering his speech in a small theatrical setting.

So is this a great movie or did someone merely use a camera to record a great lecture?

Even some of the more visual sight gags (including a “Simpsons”-like animated short that illustrates some of the theories) are taken verbatim from the slide show. Unlike Morgan Spurlock’s “Super Size Me,” which benefited greatly from inventive original material to spice up stretches of potentially dry data, Guggenheim seems content to let Gore do most of the work.

Gore is really the only “character” throughout the project. “Truth” is basically an international travelogue centering on the former investigative reporter while he presents his findings. These engagements are interspersed with ruminations from his family home in Tennessee about the fragile beauty of nature and some very powerful introspection involving family tragedies.

Throughout the movie Gore is rendered as sincere, good-natured and humorous. (“I’m Al Gore. I used to be the next president of the United States.”)

Funny, I remember the man coming across as a total stiff during the 2000 election.

If the same guy who is showcased in the film had let a hint of this personality leak through his blow-dried political image, he might have captured the Florida vote. In turn he would have earned enough electoral points to win the presidential election uncontested.

If Al Gore would have warmed up six years ago, then perhaps global warming wouldn’t be such a problem.