Guest Post by David Middleton
Breathtaking news from Nature…
Published online 9 January 2011 | Nature
The end for small glaciers
IPCC estimates of sea level rise corroborated, but large ice sheets might endure.
Richard A. Lovett
New Zealand’s mountain ranges could lose up to 85% of their glaciers by 2100. In the most comprehensive study of mountain glaciers and small ice caps to date, a team of US and Canadian scientists has projected that most of the world’s smaller glaciers will be gone by 2100.
The finding confirms that the Intergovernmental Panel on Climate Change (IPCC) — the scientific group assessing climate risk — was correct in estimating that by that date, complete or partial melting of smaller glaciers will contribute about the same amount to sea-level rise as meltwater from the giant ice sheets of Antarctica and Greenland. The study also confirms that the IPCC was wrong in stating that Himalayan glaciers would disappear by 2035.
Radić and coauthor Regine Hock of the University of Alaska in Fairbanks conducted their study by modelling the effect of climate change on every mapped mountain glacier or ice cap, using a middle-of-the-road IPCC scenario for future emissions of greenhouse gases. They then extrapolated the results to account for the fact that while Earth’s total glaciated areas are well mapped, many sections have yet to be divided into individual glaciers.
The projected contribution of each glacier’s partial or complete melting to sea level rise ranges from 8.7 cm to 16 cm, depending on the model. The IPCC’s estimates for sea level rise by 2100 ranged from 7 to 17 centimetres in its 2007 fourth assessment report.
Glaciologist Ted Scambos of the US National Snow and Ice Data Center in Boulder, Colorado says it is reassuring that the IPCC and the new study have independently reached the same conclusion. “Both could be wrong, but it gives more confidence that both are approximately right,” he says.
Ok… They used an IPCC emissions scenario. Presumably they used a climate sensitivity which conforms to the so-called consensus (~3.0°C per doubling of pre-industrial CO2). With the IPCC assumptions, they confirmed the IPCC’s projected sea level rise projections as well as predicting the demise of “small glaciers.”
Why is it a headline? They used the IPCC assumptions to model the IPCC results.
I wonder if they incorporated this little item into their model…
It appears that glacier mass balance has been on the increase since 2003… What’s up with that?
The Greenland and Antarctic ice caps have been relatively permanent features throughout the Quaternary (possibly since the Oligocene). If these ice masses melted, it would be a big deal. On the other hand, small glaciers and year-round Arctic sea ice have not been permanent features. They are relatively recent and probably rare features of the Holocene. The geological evidence indicates that the presence these small ice masses is anomalous.
The “small glaciers” of Glacier National Park, Montana may have not existed during the Holocene Climatic Optimum (HCO). The geological evidence suggests that they formed about 7,000 years ago as the Earth’s climate began to cool after the HCO.
History of Glaciers in Glacier National Park
The history of glaciation within current Glacier National Park boundaries spans centuries of glacial growth and recession, carving the features we see today. Glaciers were present within current Glacier National Park boundaries as early as 7,000 years ago but may have survived an early Holocene warm period (Carrara, 1989), making them much older. These modest glaciers varied in size, tracking climatic changes, but did not grow to their Holocene maximum size until the end of the Little Ice Age (LIA) around A.D. 1850. While they may not have formed in their entirety during the LIA, their maximum perimeters can be documented through mapping of lateral and terminal moraines. (Key, 2002) The extent and mass of these glaciers, as well as glaciers around the globe, has clearly decreased during the 20th century in response to warmer temperatures.
Climate reconstructions representative of the Glacier National Park region extend back multiple centuries and show numerous long-duration drought and wet periods that influenced the mass balance of glaciers (Pederson et al. 2004). Of particular note was an 80-year period (~1770-1840) of cool, wet summers and above-average winter snowfall that led to a rapid growth of glaciers just prior to the end of the LIA. Thus, in the context of the entire Holocene, the size of glaciers at the end of the LIA was an anomaly of sorts. In fact, the large extent of ice coverage removed most of the evidence of earlier glacier positions by overriding terminal and lateral moraines.
“Mapping of lateral and terminal moraines” clearly demonstrates that the maximum extent of the glaciers was reached during the Little Ice Age (LIA). If “in the context of the entire Holocene, the size of glaciers at the end of the LIA was an anomaly,” how can the current reduced extent be an anomaly? Is there some ideal extent? Something between the LIA maximum and the current extent?
The glaciers of Mt Ranier National Park may date back to the last Pleistocene glaciation, but they also exhibit a similar variability to those of Glacier National Park…
The size of glaciers on Mount Rainier has fluctuated significantly in the past. For example, during the last ice age, from about 25,000 to about 15,000 years ago, glaciers covered most of the area now within the boundaries of Mount Rainier National Park and extended to the perimeter of the present Puget Sound Basin.
Geologists can determine the former extent of glaciers on Mount Rainier by mapping the outline of glacial deposits and by noting the position of trimlines, the distinct boundaries between older and younger forests or between forests and pioneering vegetation. Geologists determine the age of some of the deposits by noting the age of the oldest trees and lichens growing on them and the degree of weatherring on boulders. Between the 14th century and AD 1850, many of the glaciers on Mount Rainier advanced to their farthest went down-valley since the last ice age. Many advances of this sort occurred worldwide during this time period known to geologists as the Little Ice Age. During the Little Ice Age, the Nisqually Glacier advanced to a position 650 feet to 800 feet down-valley from the site of the Glacier Bridge, Tahoma and South Tahoma Glaciers merged at the base of Glacier Island, and the terminus of Emmons Glacier reached within 1.2 miles of the White River Campground.
Retreat of the Little Ice Age glaciers was slow until about 1920 when retreat became more rapid. Between the height of the Little Ice Age and 1950, Mount Rainier’s glaciers lost about one-quarter of their length. Beginning in 1950 and continuing through the early 1980′s, however, many of the major glaciers advanced in response to relatively cooler temperatures of the mid-century. The Carbon, Cowlitz, Emmons, and Nisqually Glaciers advanced during the late 1970′s and early 1980′s as a result of high snowfalls during the 1960′s and 1970′s. Since the early-1980′s and through 1992, however, many glaciers have been thinning and retreating and some advances have slowed, perhaps in response to drier conditions that have prevailed at Mount Rainier since 1977.
The Mt. Ranier glaciers also seem to have reached their maximum Holocene extent during the Little Ice Age.
Guess what other ice feature appears to have also reached its maximum Holocene extent during the Little Ice Age?
McKay et al., 2008 demonstrated that the modern Arctic sea ice cover is anomalously high and the Arctic summer sea surface temperature is anomalously low relative to the rest of the Holocene…
Modern sea-ice cover in the study area, expressed here as the number of months/year with >50% coverage, averages 10.6 ±1.2 months/year… Present day SST and SSS in August are 1.1 ± 2.4 8C and 28.5 ±1.3, respectively… In the Holocene record of core HLY0501-05, sea-ice cover has ranged between 5.5 and 9 months/year, summer SSS has varied between 22 and 30, and summer SST has ranged from 3 to 7.5 8C (Fig. 7).
If we take the HacCRUT3 instrumental temperature record for the Northern Hemisphere and tack it on to a recent Northern Hemisphere climate reconstruction (Ljungqvist, 2009) and then scale the GISP2 climate reconstruction (Alley, 2004) to fit the instrumental record and reconstruction, we can see that the modern climate is actually rather cool relative to the rest of the Holocene…
Some may take issue with tying the GISP2 reconstruction into a hemispheric data set… But there aren’t any published Northern Hemisphere multi-proxy reconstructions that go back more than a couple of thousand years. There is a Wikipedia global reconstruction that I think was an attempt to minimise the Holocene Climatic Optimum…
The Wiki-reconstruction does attenuate the HCO a bit; but it still shows that the modern climate is down right cold in comparison to the rest of the Holocene.