Glacial Retreat of 5,000-7,000 Years Ago
I've come across a few climate articles reporting warm temperatures and high
sea levels just few millennia ago. A long time to us, just a blink of the
eye in the geologic timeframe. The most interesting reports come from the
Swiss Alps, but reports from Greenland and Peru suggest that the glacial
retreat was worldwide.
A common theme of these articles is to report how anomalous our current
temperatures are compared to the past. (Warmest in 7,000 years! Disaster
is near!) Surprisingly absent is speculation that there may be more
botanical and archaeological remains to be found should glaciers retreat
further. The report on glacial wood does point that out. It would be
refreshing to read an article looking why it was so warm then. I haven't
gone looking for any, I'm sure I'll find one soon enough.
2008 Oct 20:
Less ice in the Arctic Ocean 6000-7000 years ago
"Recent mapping of a number of raised beach ridges on the north coast of
Greenland suggests that the ice cover in the Arctic Ocean was greatly reduced
some 6000-7000 years ago. The Arctic Ocean may have been periodically ice
This includes a ruined settlement left by the Independence I Culture in
North Greenland abandoned at least 4,000 years ago.
2008 Dec 5:
Shrinking Glaciers Reveal Hidden Forests And A Warmer Climate
Uniquely old tree remains have recently been uncovered by the thawing of the
rapidly shrinking Kårsa Glacier west of Abisko in Lapland, in northernmost
Sweden. The finds show that in the last 7,000 years it has probably never been
so warm as during the last century.
"If the area hadn't been covered by a glacier all these thousands of years,
these tree remnants would never have made it. The finds yield information
indicating that the 20th century was probably the warmest century in 7,000
years. The fact that the climate is so unique during the last century means
that we must question whether this could be 100 percent the result of natural
mechanisms," says Leif Kullman, professor of physical geography, who is
directing the project.
Pines and birches grew on the site of the glacier during parts of or perhaps
the entire period between 11,800 and 7,000 years ago. This is shown by carbon
14 dating of the remains of trees that have now been uncovered. During that
period, the glacier did not continuously exist, and the climate was warmer than
at any time afterward.
2008 Oct 12:
Glacier melts are erasing climate record
"The largest glacial ice cap in the tropics, Quelccaya, lies in Peru. As it's
been retreating, it occasionally uncovers surprises that had been buried as
the glacier grew. Melting recently uncovered one wetland region that had been
buried under ice for more than 5,000 years, revealing some 50 different
members of the botanical community that once thrived there."
Holocene optimum events inferred from subglacial sediments at
Tschierva Glacier, Eastern Swiss Alps
The lead author of this article is Ulrich Joerin, a scientist studying wood
that is being released by the glacier retreat in the Alps. Much of this wood
has been transported downhill by the glaciers. This means that there used to
be forests in areas that are now glaciated. In this paper he reports "Three
periods of glacier recession were detected, which occurred around 9200 cal yr
BP, from 7450 to 6650 cal yr BP and from 6200 to 5650 cal yr BP. These periods
are called Holocene optimum events (HOE)."
- 2007 Nov 1:
Western Canada's Glaciers Hit 7000-Year Low
"Koch compared the kill dates of the trees in the southern and northern Coast
Mountains of British Columbia and those in the mid- and southern Rocky
Mountains in Canada to similar records from the Yukon Territory, the European
Alps, New Zealand and South America. He also looked at the age of Oetzi, the
prehistoric mummified alpine "Iceman" found at Niederjoch Glacier, and
similarly well-preserved wood from glaciers and snowfields in Scandinavia.
The radiocarbon dates seem to be the same around the world, according to
Koch. It's important to note that there have been many advances and retreats
of these glaciers over the past 7000 years, but no retreats that have pushed
them back so far upstream as to expose these trees."
- 2007 Feb:
Ice-borne prehistoric finds in the Swiss Alps
reflect Holocene glacier fluctuations
This paper reports on archaeological finds exposed in Switzerland dating as
far back as 4,900 years ago. It also reports on object dating back to
other more recent glacial retreats.
On a bigger scale, a paper in The Holocene, Multicentury glacier
fluctuations in the Swiss Alps during the Holocene by Ulrich E. Joerin,
Thomas F. Stocker, and Christian Schluechter reports "A comparison with other
archives and dated glacier advances suggests 12 major recession periods
occurring at 9850- 9600, 9300-8650, 8550-8050, 7700-7550, 7450-6550, 6150-5950,
5700-5500, 5200-4400, 4300-3400, 2800-2700, 2150-1850, 1400-1200 cal. yr BP."
- 2005 Nov 18:
Archaeological Finds in Retreating Swiss Glacier
This is from Climate Audit, one of the more scientifically oriented skeptic
blogs. This has earlier references to the paper above and other work.
2005 May 23:
A New Alpine Melt Theory
"The Alpine glaciers are shrinking, that much we know. But new research
suggests that in the time of the Roman Empire, they were smaller than
today. And 7,000 years ago they probably weren't around at all. A group of
climatologists have come up with a controversial new theory on how the Alps
must have looked over the ages."
The central figure in this article is Ulrich Joerin, lead author of a
2008 paper above. A similar article is
Green Alps instead of perpetual ice about work by Juerin collaborator
Oetzi, the glacier man
Oetzi is the hunter found in 1991 when his final resting spot was exposed
5500 years after his death. This site has several pages with some of the
most recent work on the body and its accoutrements.
- 2013 Mar 17:
Peru: A failed prediction
Glaciologist Lonnie Thompson, from Ohio State University, has long been
sounding the alarm about disappearing glaciers.
article in Science Daily reported on
his recent observations that suggest that the entire [Peruvian
Qori Kalis] glacier [in the Quelccaya ice cap] may likely be gone within the
next five years, providing possibly the clearest evidence so far of global
Ancient plant beds have been newly uncovered as the ice retreats. The first
were discovered in 2002, more are uncovered each year, and carbon dating
indicates that most have been buried for at least 5,000 years.
(See the 2008 Oct 12 entry above.)
In late 2012, photos show little change, so perhaps the current retreat is
slowing down. At any rate, the glacier "may likely" be there for several
Semi off topic links:
I hadn't looked hard, but I hadn't come across an
information source for North American glaciers. I found
Glacier Mass Balance in a blog entry. The site concentrates on the
North America's North Cascades, but has links to mass balance information
from wider areas. The data thins out going before 1980, so most of it covers
the warming phase of a PDO cycle and no data is included from before 1890
or so. However it is a good source of modern glacier information.
A very good reference site for Swiss glaciers is maintained by the Swiss Federal
Institute of Technology - Zurich. Its data goes back to the late
1800s when glacial flow first began to be studied.
Contact Ric Werme or
return to his home page.
Last updated 2013 March 17, originally written 2008 December 6.