Arctic Ice Melt Setting Off Climate Change Cascade

Arctic Ice Melt Setting Off Climate Change Cascade



BOULDER, Colorado, March 19, 2007 - Arctic sea ice that 
has been shrinking for decades may have reached a tipping 
point that could trigger a cascade of climate changes reaching 
Earth's temperate regions, finds a new study from the 
University of Colorado at Boulder. 
Dr. Mark Serreze, a senior research scientist at CU-Boulder's 
National Snow and Ice Data Center who led the study 
synthesizing results from recent research, said Arctic sea ice 
extent has been decreasing in every month since 1979, when 
satellite recordkeeping began. 
Serreze and his team attributed the loss of ice, about 38,000 
square miles annually as measured each September, to rising 
concentrations of greenhouse gases and strong natural 
variability in Arctic sea ice. 
Dr. Mark Serreze is a research professor of geography with the 
University of Colorado-Boulder and a senior research scientist 
with the National Snow and Ice Data Center. 
"When the ice thins to a vulnerable state, the bottom will 
drop out and we may quickly move into a new, seasonally 
ice-free state of the Arctic," Serreze said. "I think there is 
some evidence that we may have reached that tipping point, and 
the impacts will not be confined to the Arctic region." 
The review paper by Serreze and Julienne Stroeve of 
CU-Boulder's NSIDC and Dr. Marika Holland of the National 
Center for Atmospheric Research titled "Perspectives on the 
Arctic's Shrinking Sea Ice Cover" appears in the March 16 
issue of the journal "Science," published by the American 
Association for the Advancement of Science. 
"Given the growing agreement between models and observations, 
a transition to a seasonally ice-free Arctic Ocean as the 
system warms seems increasingly certain," the researchers 
wrote in "Science." 
"The unresolved questions regard when this new Arctic state 
will be realized, how rapid the transition will be, and what 
will be the impacts of this new state on the Arctic and the 
rest of the globe," they wrote. 
"We're seeing more melting of multi-year ice in the summer," 
said Stroeve. "We may soon reach a threshold beyond which the 
sea ice can no longer recover." 
"We have already witnessed major losses in sea ice, but our 
research suggests that the decrease over the next few decades 
could be far more dramatic than anything that has happened so 
far," said Holland. "These changes are surprisingly rapid." 
Dr. Marika Holland is a scientist in the Oceanography Section 
of the National Center for Atmospheric Research. 
The potential for such rapid ice loss was highlighted in a 
December 2006 study by Holland and her colleagues published in 
the journal "Geophysical Research Letters." In one of their 
climate model simulations, the Arctic Ocean in September 
became nearly ice-free between 2040 and 2050. 
Sea ice is frozen seawater that floats on the ocean surface. 
Covering millions of square miles, sea ice forms and melts 
with the polar seasons, affecting both human activity and 
biological habitat. 
Arctic sea ice extent is defined as the total area of all 
regions where ice covers at least 15 percent of the ocean 
surface. 
In the Arctic, some sea ice persists year after year, while 
almost all Southern Ocean or Antarctic sea ice is "seasonal 
ice," meaning it melts away and reforms annually. Sea ice in 
the Arctic appears to play a more crucial role in regulating 
climate, according to the NSIDC. 
Arctic sea ice summer minimum in September 2000, based on 
simulations produced by the Community Climate System Model. 
       
Studies have linked Arctic sea ice loss to changes in 
atmospheric patterns that cause reduced rainfall in the 
American West or increased precipitation over western and 
southern Europe, said Serreze, who is a fellow with 
CU-Boulder's Cooperative Institute for Research in 
Environmental Sciences. 
The decline in Arctic sea ice could impact western states like 
Colorado by reducing the severity of Arctic cold fronts 
dropping into the West and reducing snowfall, impacting the 
ski industry and agriculture, he said. 
"Just how things will pan out is unclear, but the bottom line 
is that Arctic sea ice matters globally," Serreze said. 
Passive microwave satellite data reveal that, since 1979, 
Arctic ice extent has decreased about 3.6 percent per decade, 
but in recent years, satellite data indicate an even greater 
reduction in regional ice cover. 
In September 2002, sea ice in the Arctic reached a record 
minimum, according to a 2003 study by Serreze and his team. 
That year the sea ice extent was four percent lower than any 
previous September since 1978, and 14 percent lower than the 
1979-2000 mean. 
In the past, a low ice year would be followed by a rebound to 
near-normal conditions, but 2002 was followed by two more 
low-ice years, both of which almost matched the 2002 record. 
Arctic sea ice summer minimum in September 2040, based on 
simulations produced by the Community Climate System Model. 
                 
Taking these three years into account, the September ice 
extent trend for 1979-2004 declined by 7.7 percent per decade, 
according to a 2005 study by a research team headed by 
Stroeve. 
The year 2005 set a new record low for Arctic sea ice, 
dropping the estimated decline in end-of-summer Arctic sea ice 
to approximately eight percent per decade. 
Because temperatures across the Arctic have risen from two 
degrees to seven degrees Fahrenheit in recent decades due to a 
buildup of atmospheric greenhouse gases, there is no end in 
sight to the decline in Arctic sea ice extent, said Serreze. 
"While the Arctic is losing a great deal of ice in the summer 
months, it now seems that it also is regenerating less ice in 
the winter," said Serreze. "With this increasing 
vulnerability, a kick to the system just from natural climate 
fluctuations could send it into a tailspin." 
In the late 1980s and early 1990s, shifting wind patterns from 
the North Atlantic Oscillation flushed much of the thick sea 
ice out of the Arctic Ocean and into the North Atlantic where 
it drifted south and eventually melted, he said. 
Computer models predict ice sheets like this one on Ellesmere 
Island, located north of Greenland, could melt faster than 
expected. 

The thinner layer of "young" ice that formed in its place 
melts out more readily in the succeeding summers, leading to 
more open water and more solar radiation being absorbed by the 
open ocean and fostering a cycle of higher temperatures and 
earlier ice melt, he said. 
"This ice-flushing event could be a small-scale analog of the 
sort of kick that could invoke rapid collapse, or it could 
have been the kick itself," Serreze said. "At this point, I 
don't think we really know." 
Researchers also have seen pulses of warmer water from the 
North Atlantic entering the Arctic Ocean beginning in the 
mid-1990s, which promote ice melt and discourage ice growth 
along the Atlantic ice margin. 
Serreze said, "This is another one of those potential kicks to 
the system that could evoke rapid ice decline and send the 
Arctic into a new state." 
"As the ice retreats, the ocean transports more heat to the 
Arctic and the open water absorbs more sunlight, further 
accelerating the rate of warming and leading to the loss of 
more ice," Holland explains."This is a positive feedback loop 
with dramatic implications for the entire Arctic region." 

---