Hundreds of thousands of years are locked away within the ice crystals that make up every glacier on Earth. The glaciers chronicle the history of the world, but drop by melting drop, they are vanishing.

“It’s equivalent to losing the only library on Earth that tells us what was happening in the Greek period,” said Paul Mayewski, director of the Climate Change Institute at the University of Maine.

As Earth warms, the very glaciers that can tell scientists what caused similar climate changes in the past are disappearing. For glaciologists like Mayewski, it’s literally a race against time.

Of all the climate records available, ice cores – long, narrow cylinders from drill holes reaching miles below the surface of glaciers – offer the clearest glimpse into past climates.

Each winter’s snow is compacted and becomes a distinct layer, much like a tree ring. Historical remnants such as the layer of ash from the eruption of Mount Vesuvius in A.D. 79, can help researchers assign years to the various layers.

But the science of glaciology advanced exponentially after particularly long “perfect” ice cores from Greenland were extracted in 1989. Frequently, portions of cores will have melted and refrozen, distorting the layers. But these 2-mile long cylinders from Greenland offered a precise record for most of the past 110,000 years, said Mayewski, who was a member of the team that drilled the holes.

By matching the characteristics of ice layers with the direct temperature and precipitation measurements available for the past century, scientists were able to “calibrate” the ice record in the cores for the remaining 109,900 years.

“It’s not 100 percent foolproof, but neither is looking at instrument records,” said Kirk Maasch, an atmospheric scientist with the institute.

In addition to considering the color and thickness of the layers, researchers analyze the chemical makeup of the snow itself, which can reveal important clues about the atmosphere through which it fell. For instance, the presence of sodium and chlorine can indicate a particularly stormy period, when more sea salt ends up in the ice.

“Snow is not just H2O,” Maasch said, estimating that ice core analyses consider many major and minor elements.

The Greenland ice cores, and many shorter records from around the world, definitively proved that Earth’s climate can shift quickly – with temperatures rising or dropping by dozens of degrees in just a few years. Such a change today would be comparable to Maine developing the climate of northern Virginia by 2008.

The idea of this rapid climate change turned the world of geology on its head. Mountains grow and canyons develop by fractions of inches each year. For decades, glacier experts had believed that climate behaved in the same way.

Now researchers are working to understand why rapid climate changes occur. But their research depends on collecting more ice cores from rapidly melting glaciers scattered from Patagonia to China to the Arctic.

In 1979, Mayewski conducted his research in Asia at elevations of 15,000 feet. Today, he must climb to 18,000 or 20,000 feet to find the same quality of ice.

“A lot of the sites that we could have sampled 20 years ago are gone,” he said.

Today, scientists have enough data to predict what Earth’s climate will look like in 10,000 years. But to make predictions on a fine enough scale for governments to make plans, researchers need to double their efforts to understand how past changes occurred, Mayewski said.

Information about how climate change affected the Southern Hemisphere is seriously lacking, and retreating glaciers in Asia, Canada, Alaska, New Zealand and South America still contain valuable data, he said.

“It would be nice to get these records before the whole thing disappears,” Maasch said.