The recent study by the Intergovernmental Panel on Climate Change report issued what it calls a code red for humanity due to increasingly extreme heat waves and record temperatures.
More than 80% of Greenland — an area roughly three times the size of Texas — is covered by an ice sheet up to 2 miles thick. Satellite imagery confirms the ice sheet is thinning due to glaciers speeding up and discharging more ice than they accumulate through snowfall, a process known as dynamic thinning.
PETERMANN’S ACCELERATING FLOW: The Petermann Glacier in northwest Greenland is an outlet glacier — a tongue of ice that extends from an ice cap. Outlet glaciers empty into an open area or ocean and typically occupy an irregular depression or fjord. The Petermann drains 7% of Greenland’s ice sheet and its flow rate is increasing.
The upper catchment is a portion of ice cap 60 miles wide and up to 1.8 miles thick. Its base is grounded on bedrock, much of which has been depressed below sea level by its immense weight. It slowly flows toward the edge of the ice cap.
The fjord is a water-filled depression in the bedrock into which the glacier flows. It is 18 miles wide at the ice cap and 9 miles as it nears the sea. Known as the grounding line, the point at which the glacier’s ice begins to float is about 50 miles up the fjord from its snout.
1. Inland ice: With the glacier flowing faster downstream and thinning, inland ice discharge is dramatically increased, accelerating the Greenland ice sheet’s rate of depletion.
2. Sidewall drag: Friction on fjord walls helps to stabilize the floating ice shelf and is transmitted upstream, where it affects the rate of flow of inland ice into the glacier. Reduced sidewall drag leads to an accelerated flow of inland ice, which promotes dynamic thinning.
3. Melting: Warmer air and ocean-water temperatures constantly erode the floating ice shelf as it moves down the fjord. Toward its end, the ice is less than 100 feet thick in places. Its stability will weaken if warmer water hastens underwater melting.
Scientists are especially concerned about an 6.8-mile long, 880-yard wide crack in the floating ice shelf that’s moving closer to the glacier front. If it cracks off and becomes a giant iceberg, sidewall drag will decrease for the remaining ice shelf and inland ice flow and dynamic thinning will gather pace.
ALPINE GLACIERS IN RETREAT
Glaciers in mountain regions around the globe began to decline at the end of the Little Ice Age (1550-1850) and their retreat has gathered pace since 1980. While a minor consideration in sea-level-rise calculations, alpine glacier retreat affects the amount of freshwater available for human consumption, agriculture and for natural ecosystems. The main types of alpine glaciers are shown below.
Piedmont glaciers from where valley glaciers spill out onto flatland at the base of the mountain. A lobe of ice (1) spreads out over the adjacent lowland, or piedmont zone, below the glacier’s restraining valley walls (2). Much of the glacier surface is at a low altitude and may show signs of melting.
Valley glaciers are replenished by year-round snowfall in a mountaintop accumulation area (3). The weight of ice, the slope and gravity combine to push the glacier slowly down the mountain. Sediments and boulders pulled into the glacier’s base from a coarse wet “sandpaper,” which carves out a characteristic U-shaped valley. Debris known as lateral moraine (4) is deposited at the glacier’s sides and terminal moraine (5) is left at its end, or snout.
Cirque glaciers are the smallest of the alpine glaciers, ranging in size from a few hectares to square miles. They form in a steep amphitheater (6), or cirque, and are confined there because their accumulation area (7) isn’t large enough to collect sufficient snow to feed a glacier tongue.
Greenland’s loss of ice over the centuries: If the Greenland ice sheet melted, scientists estimate that sea level would rise about 20 feet.
A team of scientists spent weeks on the Petermann Glacier using state-of-the-art equipment to study physical characteristics and dynamics.
1. GPS trackers: Several GPS units were placed at various locations along the glacier. Each tracker records the coordinates of points on the ice over a period of time to measure the glacier’s flow rate.
2. Radar: Scientists paddled kayaks along the largest of the floating ice shelf’s surface meltwater streams. They used ice-penetrating radar to measure the thickness of the ice shelf. Data collected will help researchers to determine the rate at which the ice is thinning.
Time-lapse photos: Scientists positioned a camera on an adjacent clifftop and took photos of the glacier at various time intervals to record its movement.
ADCP sensor: A sonar device that recorded underwater currents at a range of depths.
CTD sensor: This 3-foot-long cylindrical instrument was lowered into the icy waters for the fjord to measure temperature, depth pressure, salinity and water density.
Sources: Dr Alun Hubbard; Science Daily; Google Earth and NASA and The New York Times
ILLUSTRATIONS BY JEFF GOERTZEN, AUSTRALIAN GEOGRAPHIC
Source: Orange County Register