Glaciers are shrinking so rapidly we might have to change the definition of the word "glacial."

To proceed at a glacial pace nowadays means to move backwards at a rapidly accellerating rate - like, say, the Eagles.

The process is chronicled in the new documentary "Chasing Ice," which uses time-lapse photography to show just how drastically fast ice sheets up yonder are turning to water, raising sea levels.

But wait, you say, not ALL glaciers are receding. Some are advancing, right? Yes. Of the 4,000 glaciers in the Yukon, for example, 3,996 are declining (or have disappeared). Four are advancing.

If this were the stock market, it'd be a crash.

"Chasing Ice" is built around the concept that seeing is believing. It's the brainchild of photographer James Balog, a former climate change skeptic whose multiyear project to photograph ice melt turned him into a believer.

So did discussions (excerpted here) with scientists who specialize in analyzing ice - digging out core samples (with captured air particles) that show how the atmosphere has changed over the last couple hundred thousand years. Contemporary greenhouse gas levels are off the charts, they say, and coincidentally so is the prevalence of warm air and ice melt.

Moslty, though, "Chasing Ice" is a collection of spectacular, arresting images. Staggered pictures that show you the massive scale of ice, some rare footage of immense ice shelves falling into the ocean.

Collecting these images was difficult - Balog and his crew spent much time and effort installing custom built cameras in inhospitable places (Alaska, Montana, Iceland, Greenland). And the movie spends a little too much time documenting this process. And way too much time with Balog's personal life, his knee problems, his speaking engagements, etc. Testimonials about his courage, talent, achievement start to make you wonder about the movie's primary subject.

"Chasing Ice" closes well, though, building momentum and focus as it goes, and it wraps with a big money shot - surveillance footage of an Alaskan ice shelf as big as Manhattan collapsing into the sea.

The movie opens as scientists warn that the arctic permafrost is thawing, releasing even more greenhouse gas into the atmosphere.

Permafrost. Another definition we'll have to change.

Blog: philly.com/KeepItReel