DiCaprio, of course, is hardly the first actor to lend his celebrity to promoting the issue. "Years of Living Dangerously," for example -- which returns on National Geographic Channel, moving from Showtime -- enlisted a host of stars to explore different environmental concerns.
Still, as the U.N. Messenger of Peace, DiCaprio brings something extra -- including his admitted pessimism -- to the material, as well as connections that land him on-camera interviews with President Obama, Pope Francis, U.N. Secretary General Bank-Ki Moon, entrepreneur Elon Musk and Secretary of State John Kerry, as well as a number of top climatologists.
Anticipating criticism, "Before the Flood" preemptively includes a montage of climate-change deniers in media (Rush Limbaugh, Fox News' Greg Gutfield and Sean Hannity) who will surely dismiss this as more Hollywood hysteria from a limousine liberal.
DiCaprio, however, is clearly no Leo-come-lately but rather puts in the work and time -- visiting five continents, including the Arctic, China and India. He recalls his introduction to the issue more than two decades ago by then-Vice President Al Gore, which is appropriate, since "Before the Flood" is in many ways a decade-later sequel to "An Inconvenient Truth," including its closing suggestions about how an ordinary consumer can help make a difference.
Yet if Gore's movie played like a warning, "Before the Flood" -- directed by Fisher Stevens -- feels gloomier, if not entirely defeated. "We keep getting inundated with catastrophic news about the environment every single day," DiCaprio says. "Things have taken a massive turn for the worse."
As a movie star and activist, DiCaprio is certainly a legitimate target for criticism, including the concerns raised
by his foundation's alleged ties to a Malaysian embezzlement scheme. But when it comes to climate change, he's anything but a dabbler or dilettante.
Compared to "Before the Flood's" dour tone, "Rats" feels like a relative lark, a shrewdly timed entry for Halloween.
Inspired by Robert Sullivan's book, Spurlock has taken the horror-movie conceit to heart -- think the 1971 horror classic "Willard," in documentary form -- down to the cheeky filmmaking approach, including horror-style musical cues, edits and camera angles.
Get past all that, though, and "Rats" really comes across as something of an admiring ode to these little vermin, a tribute to how resourceful they are in evolving and circumventing means of exterminating them.
Like "Before the Flood," Spurlock's investigation takes him far and wide, including the U.K., India and Cambodia. Still, for a U.S. audience the most creepy interlude might be a simple nighttime tour of New York City, where a poked pile of garbage bags sends dozens of rats scurrying down sewer grates.
Moreover, there's a stomach-turning autopsy in a lab, extracting internal parasites that help explain how rats spread disease among human populations.
If there's a real star of "Rats," it's Ed Sheehan, a gruff Brooklyn exterminator who puffs away on a cigar while talking about how smart rats are -- and how much harder they're becoming to kill. "They're scary," he says, "but I gotta respect them."
Once they get over that chill up their spines, those who see "Rats" will likely feel the same way.
"Before the Flood" will premiere in New York and Los Angeles on October 21. It airs October 30 at on National Geographic Channel. "Rats" premieres October 22 at 9 p.m. on Discovery Channel.