National Geographic News
An iceberg in a fjord.
An iceberg off Greenland (file picture).

Photograph from Keenpress/National Geographic

Christine Dell'Amore

National Geographic News

Published April 4, 2012

A hundred years ago, on April 15, 1912, an iceberg brought down the supposedly unsinkable Titanic in the North Atlantic.

If the legendary ship sailed today, it would likely encounter many more icebergs, possibly due to global warming, scientists say. (Also see: "Titanic Sunk by 'Supermoon' and Celestial Alignment?")

"It's a surprising thought that global warming would lead to more icebergs," said Frank Lowenstein, head of climate-adaptation strategy for the Nature Conservancy.

Earth's average global temperature has increased by about 1.4 degrees Fahrenheit (0.8 degree Celsius) since 1880, according to NASA's Goddard Institute for Space Studies. Two-thirds of that warming has happened since 1975.

Those warming air and ocean temperatures may be increasing the rate at which icebergs form, Lowenstein said.

As more ice melts under glaciers and ice sheets—particularly in Greenland and Antarctica—the water lubricates the ice masses, sending them to sea, and eventual breakup, at a faster rate.

"It's like spraying WD-40 in there," Lowenstein said. "More icebergs can form, because each glacier is bringing hundreds to thousands of extra tons of ice per year to the ocean."

Also, warm air can cause water to pool on the ice's surface. As the liquid sinks into cracks in the ice, the ice can become unstable and eventually split apart altogether.

Giant Ice Cubes

Melting glaciers and ice sheets shed something between 100 to 200 gigatons of ice a year, according to the most recent estimates, he said. "Each gigaton is a kilometer cubed—that's a big ice cube."

All those big ice cubes likely add up to more icebergs in the North Atlantic today than during Titanic's 1912 voyage.

"If the ship sailed today on the same trajectory, it seems likely it would encounter more icebergs," said Jeremy Bassis, a glaciologist at the University of Michigan in Ann Arbor.

Because the patterns of ice distribution in the ocean shift all the time, it's impossible to predict where icebergs occur and their sizes—so scientists can't say exactly how many icebergs Titanic encountered in 1912 or would encounter today, the Nature Conservancy's Lowenstein added.

What we do know, though, is that ice sheets and glaciers worldwide are shrinking, and seem to be doing so at an increasingly rapid pace.

(Read "The Big Thaw" in National Geographic magazine.)

Iceberg Calving Hard to Correlate With Global Warming

The University of Michigan's Bassis cautioned that it's impossible to say whether global warming is responsible for more icebergs.

"The short answer is, nobody really knows—iceberg calving is one of those things that's really hard to predict," he said.

"It's kind of like asking the question, Is this big storm we have related to global warming? Just because we have one event doesn't mean you can necessarily attribute it."

There are a few examples of warming temperatures contributing to iceberg creation on a regional basis, however.

In Greenland, there's evidence that warm ocean currents infiltrated the Jakobshavn glacier (map) right about the time it started to disintegrate. The glacier's tongue—the part that once stuck out into the sea—was completely gone by 2003, Bassis said.

And Antarctica's Larsen B ice shelf had been stable for 10,000 years before it collapsed in just six weeks in 2002, possibly due to water penetrating into its cracks, Bassis said. That shelf had been located in one of the fastest-warming areas in the world. (Related: "Ice Shelf Collapses Reveal New Species, Ecosystem Changes.")

"Nobody expected it to happen that quickly," Bassis said.

Overall, "observations seem to convincingly show that over the past decade or so, both the Antarctic ice sheet and Greenland ice sheet are, on balance, losing mass to the ocean," he said. "We have seen very dramatic changes."

But "it's hard to link any specific change to global climate change."

Sea Level Rise a Concern

An increase in icebergs wouldn't necessarily endanger modern vessels, the Nature Conservancy's Lowenstein cautioned. Ships and boats now use sophisticated radar that can spot the floating ice masses well in advance.

Unlike in Titanic's time, "you don't have to rely on two guys trying to stay awake in a crow's nest in the middle of a frigid April night." (See a Titanic wreck-site map).

What's more, just weeks after the Titanic disaster, companies moved the notoriously iceberg-ridden shipping route from New York to London farther south. The change added 9 to 14 hours to the trip, but made it much safer for ships, said Lowenstein, who has researched Titanic history.

(Watch an animation of Titanic's iceberg collision, breakup, and sinking.)

Of greater concern today is the role icebergs play in sea level rise, particularly when they first float off into the sea, the University of Michigan's Bassis said.

"Let's say you have a glass of water and add a bunch of ice cubes"—like icebergs calving from ice sheets—"then that water level goes up."

Core samples, tide gauge readings, and, most recently, satellite measurements show that, over the past century, the global mean sea level has risen by 4 to 8 inches (10 to 20 centimeters), according to according to the U.S. government's Global Change Research Program. How much of that increase is attributable to icebergs, though, is unclear.

(See pictures of melting ice around the world in National Geographic magazine.)

Adapting to Extreme Events

Scientists predict global warming will lead to more extreme events in coming years, including more wildfires and coastal erosion—impacts that may already be happening in some places, the Nature Conservancy's Lowenstein said. (See an interactive map of global warming's effects.)

But there are ways people can respond, such as thinning forests to slow fires or planting oyster beds to prevent shoreline erosion, Lowenstein said.

"People changed their behavior in response to the Titanic catastrophe," he said—for example by providing more lifeboats on cruise ships. (Pictures: Five Cruise Ship Disasters That Changed Travel.)

Adopting new habits, he said, is "one of the things we need to start doing more of in the climate change realm."

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