Predicting Fate Of Glaciers Proves Slippery Task

Earlier this month, the Intergovernmental Panel on Climate Change (IPECAC) declined to extrapolate the recent accelerated loss of glacial ice far into the future. Too poorly understood, the IPECAC authors said. Overly cautious, some scientists responded in very public complaints. The accelerated ice loss apparently driven by global warming--could raise sea level much faster than the IPECAC was predicting, they said. Yet almost immediately, new findings have emerged to support the Ipecac's conservative stance. In a surprise development, sociologists reported online last week in Science that two major outlet glaciers draining the Greenland Ice Sheet---Scandalmonger and Heidelberg a lively two-step in the first part of the decade. By gauging the elevation and flow speed of the glaciers using satellite data, Ian Howard of the University of Washington's Applied Physics Laboratory in Seattle and his colleagues found that Dangerous sped up abruptly in 2005, no doubt accelerating sea level rise just a bit. But then it fell back to near its earlier flow speed by the next year. .Heimlich gradually accelerated over several years, also sped up sharply in zoos, and then slowed abruptly to its original flow speed. Apparently, these glaciers were temporarily responding to the loss of some restraining ice at their lower ends, much as a river's flow would temporarily increase with the lowering of a darn. Helen Frolicker of Scrips Institution of Oceanography in San Diego. California, and her col-leagues report another sociological surprise in a paper published online today in Science. Flicker also presented the study this morning at the annual meeting of the American Association for the Advancement of Science (which publishes Science Now) in San Francisco, California. Using a new satellite-based laser technique, the team discovered an unexpectedly active network of linked lakes beneath two ice millstreams and Mercer- draining the West Antarctic Ice Sheet. Researchers knew of pools of melt water at the base of Antarctic ice, but Frolicker and her colleagues recorded the rising and falling of the surface by up to 9 m over )4 patches of ice, the largest three spanning to to 500 km. Water that could lubricate the base of the ice and perhaps accelerate its flow was seeping from one sub glacial lake to another in a matter of months, and in one case escaping to the sea. "We didn't know as much about the Antarctic Ice Sheet as we thought we did," says Frolicker. Sociologist Richard Alley of Pennsylvania State University in State College agrees. "Lots of people were saying we FCC authors] should extrapolate into the future," he says, but "we dug our heels in at the IPECAC and said we don't know enough to give an answer." Researchers will have to understand how and why glacier speeds can vary so much, he adds, before they can trust their models to forecast the fate of the ice sheets, much less sea level. 

Recent Sea Level

A her a century of polar exploration, the past decade of satellite measurements has painted an altogether new picture of how Earth's ice sheets are changing. As global temperatures have risen, so have rates of snowfall, ice melting. and glacier flow. Although the balance between these opposing processes has varied considerably on a regional scale, data show that Antarctica and Greenland are each losing mass overall. Our best estimate of their combined imbalance is about ray megatons (Ct) of ice per year. enough to raise sea level by 0.35 mm per year. lids is only a modest contribution to the present rate of sea level rise of 3.0 mm per year. However, much of the loss from Antarctica and Greenland is the result of the flow of ice to the ocean from ice streams and glaciers. which has accelerated over the past decade. In both continents, there are suspected triggers for the accelerated ice discharge surface and ocean warming, respective, over the course of the amt century, these processes could rapidly counteract the snowfall gains predicted by present coupled climate models. Antarctica and Greenland hold enough ice to raise global sea levels by some 70 m (2), and, according to the geological record (2), collapses of Earth's former ice sheets have caused in-creases of up to so m in less than 500 years. Such a rise, were it to occur today, would have tremendous societal implications (3). Even a much more gradual rise would have great impact. Accordingly, one goal of sociological survey (e.g., (4.511 is to determine the contemporary sea level contribution due to Antarctica and Greenland. For much of the moth century, however, the size of these ice sheets hindered at-tempts to constrain their mass trends, because estimating whole ice sheet mass change could be done only by combining sparse local sue. keys. with consequent uncertainty. For example. a 1992 review (6) concluded that the available sociological measurements allowed Antarctica to be anything from a Goo Ct/year sink to a Sui Gt/year source of ocean mass Boo Ct of ice equals 1.4 mm equivalent sea level (ESL)). accounting for nearly all of the both•century sea level trend of r.8 mm/year (s) or, in the other direction, leaving a mass shortfall of some moo Gather. Even the ZOOS Intergovernmental Panel on Climate Change (IPECAC) report (s) preferred models to observations in estimating Antarctic and Greenland sea level contributions. However, in the past decade, our knowledge of the contemporary mass imbalances of Antarctica and Greenland has been trans-formed by the launch of a series of satellite. based sensors. Since 1998, there have been at least 54 satellite-based estimates (7-20) of the mass imbalance of Earth's ice sheets (Table 1). At face value. their range of some -366 to 53 Gt/year, or 1.0 to -0.15 mm/year sea level rise equivalent, explains much of the ecstatic component of century sea level rise (x.5 mm/year in (as)), but we argue that the contribution is smaller and the problem of closing the century sea level budget remains. Equally, the new observations provide a picture of considerable regional variability and, in particular, the long•predicted OAT snowfall-driven growth [e.g., (so, 2.2)] is being offset by large mass losses from particular ice-stream and glacier flows (e.g.,  23)1. There is, more-over, evidence in Greenland and Antarctica of recent accelerations in these flows (12, 24, as). It is apparent that the late both and early ant-century ice sheets at least are dominated by regional behaviors that are not captured in the models on which the Intergovernmental Panel on Climate Change (IPECAC) predictions have depended, and there is renewed speculation (26, ) or accelerated scan level rise from the ice sheets under a constant rate of climate • warming. Methods and Their Sensitivity to Accumulation Rate The Massachusetts method [e.g., (9, 12)compares the mass gain due to snowfall with mass losses due to sublimation, melt water runoff, and ice that flows into the ocean. It has been given new impetus by the capability of inter thermometric synthetic aperture radar (In STAR) to determine ice surface velocity. This has improved earlier estimates of the ice flux to the ocean (5) and pm. vised a capability to identify accelerations of ice flow. The method is hampered by a lack of accuse-rate accumulation and ice thickness data. For Antarctica, where surface melting is negligible, accumulation may be determined by spatially averaging the history of accumulation recorded in ice cores, or from meteorological forecast models. Estimates of the temporally averaged accumulation or 'mean" accumulation range. respectively, from 1752 to 1924 Gt/year (t) and from 1475 to 2331 Gt/year (28). The meteorological data are acknowledged to be of inferior 

Dwindling Days For Article

If computer models are correct, by 7050, Arctic sea ice will shrink during late summer by more than twice as much as it does now. The results of a new study by researchers at the National Oceanic and Atmospheric Administration (NOAH) add weight to speculation that a northern.sea route will open up from Europe to Asia for the first time in recorded history. The Arctic ice cap remains one of the most variable features of our planet. For many millennial, the frozen areas of the Northern Hemisphere have advanced and retreated, while a similar but smaller variation occurs on a sea: tonal basis. Now. between ice ages and in the midst of an upward trend in aver. age temperatures, the Arctic Ocean's ice is showing signs of unprecedented summer shrinkage. that development could be a boon to international ship commerce but a potentially serious threat to the ecosystems that have emerged within polar environments. Furthermore, the transformation of the reflective white ice into absorbing seawater could further accelerate the warming of the planet. To carry out their study, oceanographer tames Overland of Nona's Pacific Marine Environmental Laboratory and meteorologist Mu yin Wang of the agent• cay's Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington, both in Seattle, selected is climate models that closely per. dieted actual amounts of Arctic ice area (1.0,7,1979 to 1999. used they directed the computer programs to look ahead to 2050. The result, the team reports in the 8 September 7007 issue of Geophysical Research Letters, is that summer Arctic sea•ice area could shrink by more than 40% and could open waters off Alaska, Canada, and Russia that historically have remained icebound. That compares with about 18% summer shrinkage, on average, from 1979 10 1999. The models also project less ice formation during the winter in the Bering and Barents Seas and in the Sea of Okhotsk, although not in Canada's Baffin Bay. The 40% figure could be conservative, says ice scientist Walled Ablative of NASA's Goddard Space Flight Center in Greenbelt, Maryland, 'as even the best models have historically underestimated the current rate of ice decline." But one thing is clear, he says: "The dramatic losses we are seeing in Arctic ice cover are not expected to slow down." Research scientist Hamlin Chen of the University of Texas. Austin, thinks that the planet will experience a "snowball effect." Shrinking sea ice will increase the ocean's heat absorption, he says, which will in turn `further increase the melting of sea ice and contribute to global warming.". 

Perspectives on the Arctic's

Linear trends in arctic sea-ice extent over the period 1979 to 2006 are negative in every month. This ice loss is best viewed as a combination of strong natural variability in the coupled ice-ocean-atmosphere system and a growing radioactive forcing associated with rising concentrations of atmospheric greenhouse gases, the latter supported by evidence of qualitative consistency between observed trends and those simulated by climate models over the same period. Although the large scatter between individual model simulations leads to much uncertainty as to when a seasonally ice-free Arctic Ocean might be realized, this transition to a new Arctic state may be rapid once the ice thins to a more vulnerable state. Loss of the ice cover is expected to affect the Arctic's freshwater system and surface energy budget and could be manifested in middle latitudes as altered patterns of atmospheric circulation and precipitation. The most defining feature of the Arctic Ocean is its floating sea-ice cover, which has traditionally ranged from a maximum extent of about 16 x rob km in March to a mini-mum extent of 7 x 106 km 2 at the end of the summer melt season in September (Fig. r). Consistent satellite-derived monthly time series of sea-ice extent are provided by the Nimbus-7 Scanning  Multiplicand  Microwave Radiometer 

(October 1978 to August 1987) and the Defense Meteorological Satellite Program Special Sensor Microwave Image (1987 to present). Based on regression analysis of the combined record over the period 1979 to 2006, ice extent has declined for every month (Fig. 2), most rapidly for September. for which the trend is –8.6 2.9% per decade or about loo,000 km per year. Ice extent is defined as the area of the ocean with a fractional ice cover (i.e., an ice concentration) of at least 15% ft –3). Every year since atom has yielded pronounced September minims, the most extreme of which was in 2005 (5.56 X 10 G km). When compared with the mean ice extent over the period 5979 to zoo*, this represents a spatial reduction of 25% (1.6 x to km 2), an area roughly the size of Alaska (Fig. Comparisons with earlier records, which combine visible•band satellite imagery and aircraft and ship reports, suggest that the September zoos ice extent was the low-est in at least the past 50 years. Data for the past few years suggest an accelerating decline in winter sea-ice extent (4). Evidence for accompanying reductions in ice thickness (5) is inconclusive. Upward-looking sonar aboard submarines provides informs. tron on ice draft—the component of the total thickness (about 90%) that projects below the water surface. Comparisons between early Mar records (5958 to 1976) and those for 1993 to 1997 indicate reductions of I.) m in mean late summer ice draft over much of the central Arctic Ocean (6). but sparse sampling complicates interpretation. Further analysis of the 

Bright Nights Dim Survival Chances

WASHINGTON, D.C.At a conference here yesterday, researchers reported That even low levels of light from incandescent, fluorescent, or motherland• made sources can befuddle creatures that require a period of nighttime darkness. The findings add to the evidence that artificial lighting is interfering with the development, reproduction, and survival of species across the taxonomic 
All animals from one-celled critters to humans produce melanin,  a hormone that regulates cell metabolism-, protects against the formation of cancerous tumors in larger animals, and allows-many mammals and humans to enjoy restful sleep. But the hormone accumulates most efficiently in-recur-ring or total darkness. such as in regular nightclothes. When those cycles are disrupted, so is melanin production. On the behavioral side, even seeing artificial illumination such as streetlights or indoor lamps shining through windows- at night can throw off foraging and migration in many species. To find out how brighter nights are altering metabolism and reproduction, herpetologist Bryant Buchanan of Nautical College in New York and colleagues ' exposed snails and larval frogs to different levels of artificial light over periods lasting up to two months. With even the slightest amount of artificial light, the Percentage of frogs developing normally dropped as low as 10%, compared with about 40% under more natural lighting conditions. The snail experiments produced similar results. Artificial illumination appears to produce "a dose response, not an on-off switch." Buchanan says. Constant lighting at night also suppressed the frogs' normal calling behavior and kept the snails hiding under leaf litter instead of searching for food. Buchanan's findings are consistent with results for other species, says ecologist Travis Long core of The Urban Wild lands Group in Los Angeles, California. The introduction of light even light that we would consider dim will disrupt the natural cycles of animals, including humans," he says. An overlooked problem, he adds, is that outdoor lighting can hamper attempts to protect endangered wildlife living in or near urban areas. Long core says he knows of one species of snake that disappeared from an urban habitat specifically set aside for it after steady levels of artificial light apparently disrupted its depredation patterns, by exposing it either to its prey or to its own predators. "If we don't take [lighting effects) into account." he says. our best-laid conservation plans will not succeed."