Ice Loss Signs of Change

The Cryosphere  Earth has many frozen features including – sea, lake, and river ice; – snow cover; – glaciers, – ice caps; – ice sheets; and – frozen ground.  Collectively called the "cryosphere," Earth's frosty spots play a critical role in regulating global climate.

 Throughout the cryosphere, surface temperatures remain below freezing for a portion of the year.  Direct measurements of the cryosphere can be difficult to obtain because many of these areas are remote.  Researchers use satellites to monitor changes in the global and regional climate by observing how regions of the cryosphere shrink and expand. The Cryosphere, (cont’d)

Shrinking Sea Ice  In summer, long hours of sun and warmer temperatures melt some of this ice.  During dark winter months, sea ice covers most of the Arctic Ocean.

 Arctic sea ice usually reaches maximum melt in September, and expands again in winter. Shrinking Sea Ice (cont’d)  Because sea ice is more reflective than liquid water, it regulates global climate by keeping polar regions cool.

Shrinking Sea Ice (cont’d)  Sea ice extent is decreasing due to warmer air temperatures, warmer ocean temperatures, and when ice fragments are blown out of the Arctic Ocean by wind.  As sea ice melts, the Arctic's ability to stabilize the Earth's climate declines, escalating a "feedback loop" of more solar energy absorption, higher air temperatures, and less sea ice.

Behind the Numbers  Using satellite data, researchers have determined that winter Arctic sea ice has declined by 4.3% per decade from 1979 to  Arctic sea ice is melting much faster in summer, with volumes decreasing 12.4% per decade through 2010.

 In summer 2007, the polar ice cap melted to its lowest level on record and the fabled Northwest Passage became navigable for the first time. Behind the Numbers (cont’d)

 The 2010 minimum ice extent was the third lowest since 1979, the fourth year in a row the Northwest Passage opened, and the third consecutive year of an open Northern Sea route.

 September ice extents have declined on average 30 years faster than IPCC models had predicted.  While the annual minimum sea ice extent typically occurs in September, all months have shown decreases. Behind the Numbers (cont’d)

Glacier Anatomy  Glaciers are year-round masses of snow and ice that take years to accumulate.  Found at high altitudes and latitudes around the world, glaciers move constantly but at tortoise- speed, like a slow motion river.

 Glaciers accumulate snow at higher elevations, which over time becomes compressed into ice. Glacier Anatomy (cont’d)  Where glaciers reach the ocean, this river of ice melts, breaks off, and floats away.  If melting is balanced by the accumulation of new snow, a glacier maintains equilibrium and neither grows nor shrinks.

Glacial Clues About Climate  Glaciers are key indicators of climate change: by growing or shrinking, advancing or receding, a glacier provides visible evidence of changes in temperature and precipitation.  Melting glaciers and ice sheets account for more than one-third of current sea level rise.  Research indicates that glacial ice loss has accelerated over the last decade.

Glacial Clues About Climate  The Jakobshavn Isbrae glacier, (above), is located on the west coast of Greenland. The ice front, where the glacier calves into the sea, receded more than 25 miles (40 km) between 1850 and 2010.

Glacial Clues About Climate (cont’d)  Since 1960, glaciers worldwide have lost more than 2,000 cubic miles of water.  The contribution of glaciers and ice caps to global sea level has increased from 0.03 in. (0.8 mm) per year in the 1990s to in. (1.2 mm) per year today.

 The photos above reveal the disappearance of Grinnell Glacier in Glacier National Park over the course of a century. The glacier is first documented in 1900 and again in Glacial Clues About Climate (cont’d)

Disappearing Ice Shelves and Advancing Ice Sheets  The ice shelves—slabs of frozen, floating ice hung up on islands or other geographic features—that long buttressed the ice sheets are rapidly collapsing or melting.  The Larsen B ice shelf in Antarctica—which collapsed in 2002—is one such example.  Once shelves are gone, ice sheets or their outlet glaciers can accelerate by up to eight times their advance toward the sea.

 Image Sequence of Larsen Ice Shelf Collapse:  Disappearing Ice Shelves (cont’d)

Ice Sheets and Sea Level Rise  The extent of the Greenland ice sheet that melts each summer has increased by 30% since 1979, consistent with warming air temperatures.  Melting occurred on 50% of the ice sheet during the record season in 2007.

 The loss of ice from the Greenland ice sheet has accelerated since the mid-1990s, and now contributes as much as 0.03 in. (0.7 mm) per year to sea level rise due to both melting and accelerated ice flow.  This makes up approximately half the global contribution to sea level rise from glaciers and ice caps. Ice Sheets and Sea Level Rise (cont’d)

 Changes in the Greenland and Antarctic ice sheets are critical in quantifying forecasts for sea level rise.  Since its launch in January 2003, the ICESat elevation satellite has been measuring the change in thickness of these ice sheets.

Ice Sheets and Sea Level Rise (cont’d)  Antarctica is also losing ice more quickly—especially from the West Antarctic ice sheet—as a result of accelerating ice flow.  Antarctica's current contribution to sea level rise is comparable to Greenland's.

Ice Sheets and Sea Level Rise (cont’d)  Glacial melt provides a reliable source of irrigation and drinking water, particularly late in the summer after seasonal snowpack has melted.  Much of Earth's fresh water is found in glaciers, including the polar ice sheets.  If glaciers lose mass due to melting and breaking off — particularly the Greenland and Antarctic ice sheets—the meltwater will contribute to global sea level rise.