Like tigers, their striking beauty belies incredible power. During an ice age, glaciers chew up everything in their paths, etching their signatures on landscapes like Yosemite National Park's stunning cliffs or Norway's dramatic fjords. When they recede, melting glaciers can unleash a torrent of water and debris capable of inundating downstream villages and shorelines.

Glaciers are home to iconic species such as penguins and polar bears, noted for their vast grandeur and start beauty, and most importantly – serve as nature's water tanks. Glaciers capture frozen precipitation and then release it as water through streams and rivers during warmer months.

We study how glaciers melt because better understanding their intricate water storage system provides a window into how our climate is changing. As glaciers go, so goes the Earth's temperature and sea level. The current rapid (geologically speaking) reduction in global glacier mass provides clues to the likelihood that significant and possibly catastrophic environmental changes lay ahead.

While we can't halt glacier melt, we can adapt to the environmental consequences and slow down the increase in greenhouse gas emissions that contribute to their reduction.

The Nature of Glaciers

Glacier melt is a natural phenomenon. Glaciers are accumulations of snow at higher altitudes that condense into ice and, thanks to gravity's pull, slowly move downhill. Glaciers add mass from snow, and they shrink by melting in warmer months. As glaciers inch their way downhill they often increase their rate of melt due to the lower and warmer elevation.

Warmer global temperatures can push the melt line (the altitude at which snow melts) higher and increase the rate at which glaciers shrink. Currently the two largest glacial regions -- the ice sheets of Greenland and Antarctica -- are melting more precipitously than in the past, flooding the oceans with fresh water and threatening shorelines world wide.

The melt rate of Greenland's ice sheet has increased by 30 percent during the past 30 years. In Antarctica the ice sheet is moving towards the ocean 12 percent faster than in the previous decade, prompting a sea level rise in the region of .16 inches per year.

The long-term average annual economic loss from glacier disasters or related mitigations costs are estimated to be in the order of several hundred million U.S. dollars.

Melting glaciers are responsible for one-third of the total rise in sea level, according to Andrew Fountain, Professor of Geography and Geology at Portland State University. Fountain, who travels the world studying glaciers, expects that with the current rate of melt global sea level will rise approximately one foot by 2050. (The other two -thirds of sea level rise comes from thermal expansion as water warms.)

However, a sea level rise of a few meters would submerge coastal regions around the world, as pointed out in the film "An Inconvenient Truth."

If glacier melt continues to accelerate, sufficient fresh water could be dumped into the oceans to disrupt the natural circulation of cold and warm water under the oceans, known as the thermal haline flow or the "great ocean conveyor."

This conveyor circulates warmer water from the equator to the northern Atlantic region to replace cooler seawater that sinks to the ocean floor, keeping eastern North America and western Europe warmer than their distance from the equator would otherwise suggest. Stopping this flow could cause another ice age, according to Fountain.

"It's like the first 15 minutes of the 'Day After Tomorrow,'" says Fountain, referring to the film's opening sequences depicting New York as a frozen wasteland.

"The question is, can [an ice age] happen in the next 50 to 100 years? Probably not, but maybe," Fountain says. "How much do you want to know about maybe?" says Fountain, explaining the need to further study how glaciers melt and their relationship to climate change.

"This is the scary issue for us (glaciologists). We don't have sufficient science to know what the probability of [an ice age] is." Once an ice age starts, a significant climate change could be completed within a decade and would cause a major disruption to world economies, according to Fountain.

Fountain says that we are beyond the point where we can mitigate climate change and should focus on adapting to its inevitability. Scientists don't understand environmental systems sufficiently to fully understand how greenhouse gas emissions will effect the climates, Fountain says.

Glacier's Local Effects

Even if glacier melt does not prompt a significant climate shift, changes to the natural system of holding frozen water could severely impact the inhabitants and economies of the areas near glaciers.

Melting glaciers can cause avalanches and "outburst floods" that threaten communities and slides of earth and debris that reshape the landscape and disrupt travel and commerce. A loss in glacier mass increases the likelihood of drought and water scarcity, according to United Nations report the Global Outlook For Ice and Snow (PDF).

"The long-term average annual economic loss from glacier disasters or related mitigations costs are estimated to be in the order of several hundred million US dollars," according to the report.

Lake outburst floods are the biggest local threat from melting glaciers. Glacial lakes that overflow from melting can rupture and overwhelm communities downstream.

As glaciers move downhill they burrow into the earth, uprooting vegetation and cut through the earth and rock. When they retreat by melting, they can leave behind a basin of debris and unstable dirt and gravel, according to Fountain. These basins are prone to fail during rains, sending a cascade of water and debris down the hillside, overwhelming homes, streams and roadways.

An extreme example of an outburst flood occurred in 2002, when an ice/rock avalanche with a volume of 100 million cubic meters killed more than 30 people in the Caucasus region of Russia.

As glaciers shrink and temperatures rise, the peak run-off time for fresh water from glaciers shifts to earlier in spring, and less water is available during dry summer months. In the northern hemisphere, water from glaciers "flows just at the time when you need it, in August and September that are generally the driest months," according to Fountain. But with shrinking glaciers, the likelihood of severe drought increases.

The majority of people in the world depend on water from glacier melt for food, drinking water, and irrigation, including 40 percent of the world's population who live downstream from glacier tributaries in Asia. Smaller glaciers means less water available in the summer and increasing scarcity for human comsumption, according to the U.N. report.

"Reduced water flow in the dry seasons will lead to more and longer periods with critical shortages of water for transportation, drinking water and irrigation, with consequences for trade, small and large-scale agriculture and with increased potential for disputes over sectoral and regional allocations of this diminishing resource."

What We Can Do

The rate of glacier melt is directly affected by the Earth's temperature, which is influenced by greenhouse gas emissions and a natural cyclical variation in climate. Countering climate change requires a global effort that starts with individuals and communities.

People who live downstream of glaciers and would like to protect their water supply and backyards from the effects of glacier melt can not do much on their own, according to Fountain. For example, residents of the Himalayas or northwest U.S. who cut back emissions can't protect their glaciers because of global influences. "The atmosphere is fairly well mixed," Fountain says, adding that the Western U.S. is strongly affected by emissions from China because of how the wind circulates across the globe.

Slowing down the current increase in glacier melt requires a concerted global action that should start at the grass roots level, according to Fountain. National and regional governments, industries and individuals need to increase their energy efficiency and reduce their emissions.

Individuals can start by assessing their carbon output and changing their lifestyles to improve their energy efficiency, as recommended by the Save Our Snow Foundation.

Communities and associations that campaign against and limit their own greenhouse gas emissions will be heard by the politicians who are in the best position to enact large scale change, according to Fountain. He says it is "not politically viable to reverse (the amount of) emissions," but slowing down the rate of increase to protect glaciers is an achievable goal.