Melting Planet
As ice and snow melt around the globe, scientists struggle to comprehend the often-contradictory effects of global warming.
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| Severe melting of Grinnell Glacier from Mount Gould in Glacier National Park, Mont., between 1938 and 2005. | Photo courtesy of (left) T.J. Hileman (Glacier National Park Archives) and (right) Karen Holzer (USGS). |
Often overlooked in the attention that atmospheric warming receives these days is the fate of the cryosphere. The term refers to the snow, ice, glaciers and permafrost which have a profound impact on the earth’s climate.
And it is changing at an alarming rate, according to the latest United Nations Intergovernmental Panel on Climate Change report.
The cryosphere’s mass and heat capacity plays a central part in climate as it covers most of the polar regions as well as very high and low latitudes. Warming certainly played its part in the recent retreat of the cryosphere, but cannot fully explain the extent of the melting.
Scientists say certain factors are working together to accelerate change.
“A positive feedback process occurs when a small change in a certain direction is enhanced,” explained Dr. Julie Winkler, professor of geography at Michigan State University.
The degree to which a surface reflects light from the earth—the albedo effect—varies because different surfaces absorb and reflect heat and light differently. Snow, ice and glaciers have a high albedo, reflecting vast amounts of light and heat from the planet. The exposed surface of the earth and the oceans have low albedos, absorbing much heat and light.
When the cryosphere melts and rock and soil are exposed, runaway heating occurs: melted ice and snow results in more rock and ocean to be exposed, which in turn absorb more heat. As more heat is absorbed, even more ice melts.
The Cycle Continues
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| The Gulf Stream. Photo illustration by Summi Gambhir. |
As the earth warms, ice and glaciers not only melt faster, they melt earlier, giving them less time to build up during the winter. More rock, soil and ocean are exposed for longer durations, which then trap heat at a greater rate and further amplify the melting.
The U.N. report said that glaciers are shrinking and adding to sea level rise each year, that the average annual snow cover from 1988 to 2004 was reduced by 5 percent compared to annual snow cover between 1967 to 1987 and that the Arctic extent of sea ice has decreased by 2.7 percent each decade since 1978.
The world is losing its ice and snow, and is doing so at an extremely rapid rate.
Permafrost is also affected by warming and displays similar positive feedback. Before the last ice age, the areas that are today frozen ground were grasslands, teeming with an abundance of life. When the climate changed, glaciers overran the grasslands and trapped the organic matter underground, where it slowly decomposed and converted into a gaseous state. For many years these potent greenhouse gases—such as methane and carbon dioxide—have been safely stored away from Earth’s atmosphere. But as the permafrost thaws, these gases are released back into the atmosphere, further accelerating warming.
Scientists have already witnessed the impact of positive feedbacks across the continents. The ice field atop Mount Kilimanjaro in Africa has receded mightily in the past decade. Jennifer Olson, a professor of telecommunications who is associated with the Center for Global Change and Earth Observation at Michigan State University, has seen the mountain’s landscape change during the decade she’s done research in Africa.
"The retreat of the glacier is a combination of warmer temperatures, disturbances in rainy season due to deforestation and the volcanic soil absorbing more radiation," Olson said.
Glacier National Park in Montana also has rapidly shrinking glaciers. According to the Sierra Club’s global warming and energy program, the park boasted close to 150 glaciers around 1850. Today, glaciers are rare. The number has shrunk to about 30.
Convoluted Results
As the cryosphere slowly disintegrates, water is left in its wake. A combination of more water and a warmer planet means more bad news and another positive feedback mechanism: more water vapor—a greenhouse gas—is released into the atmosphere.
Increased water vapor is not all bad because it plays the essential role in forming clouds. Clouds can both accelerate global warming and curb it. In the case of global warming, negative feedbacks, which involve a change that moves the system in an opposite direction, help slow climate change.
Clouds can reflect the sun and keep the earth cool. That is a negative feedback. But when sunlight gets past the clouds and reaches the Earth’s surface, a positive feedback takes place because the clouds hold in heat and warm the atmosphere.
Experts say that the role clouds will play in future warming is highly speculative. Much depends on the amount of clouds, where they are and their composition.
"Warmer clouds, composed of water droplets, have a net cooling effect while ice crystal clouds have a greater warming effect," Winkler said.
A cloud’s albedo is also affected by its formation, which causes much difficulty when trying to predict warming. "Models try and get as much as possible, but clouds are the really hard part... clouds are a very fine scale while the models are too coarse," Winkler said.
Troubled waters
Increased water also affects the Gulf Stream, an ocean current which transports warm waters from the equator to the eastern shores of North America, followed by an eastward movement toward northern Europe. During travel, the warm waters are in constant interaction with the atmosphere. Heat from the ocean is eventually released into the atmosphere, providing northern Europe with its current climate. The movement of the Gulf Stream into the Norwegian Sea, pivotal to the warming of northern Europe, is driven by cold, dense water sinking to the ocean bottom. “The sinking water actually creates a slight depression in the sea level of the Norwegian Sea,” said Nathaniel Ostrom, a biogeochemist at Michigan State University.
Without sinking water, the warmer waters brought by the current would head south towards the southern coast of Europe and Africa. This effect would cause northern Europe’s climate to become similar to the harsh climate of Labrador, Canada.
Increased precipitation and water runoff from melting glaciers and ice, which have inundated the ocean, have also decreased the salt content of the North Atlantic Ocean.
"Lowered salinity in the oceans means that ocean water is less dense and unable to sink," said Ostrom. "It also means that since the fresher water is less dense, the Gulf Stream may move below a lens of the cool water, blocking any interaction between the atmosphere and the warmer waters brought by the current."
Both situations will likely play out in the near future. "Ironically, global warming will bring global cooling to certain regions of the world," Ostrom said.
As scientists debate the outcome of positive and negative feedbacks, polar caps and permafrost continue to melt. Only time will tell what the changes will bring."
Matt Cimitile is a first-year graduate student in the environmental journalism program at MSU. This is his first appearance in EJ. Contact Matt at cimitile@msu.edu.
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