Birmensdorf,
24.01.2013
New Greenland ice core reveals warmer temperatures 120,000 years ago
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The Black dome, the main
NEEM camp facility which includes kitchen, dining room, and work space. (large version)
Photo: Konrad Steffen (WSL)
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NEEM automatic weather station with NEEM camp in background.
(large version)
Photo: Konrad Steffen (WSL)
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Research team of Konrad Steffen (left) with J.P. Steffenson (NEEM camp
leader), Simon Steffen (student), and Faezeh Nick (post-doc).
Photo: Konrad Steffen (WSL) (large version)
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The climate
graph shows the temperature from the previous warm interglacial period, the
Eemian (left) throughout the entire ice age to present time (right). The blue colours
indicate ice from a cold period, while the red colour is ice from a warm
period. The new results show that during the Eemian period, 130 to 115 thousand
years ago, the climate in Greenland was around 8 degrees C warmer than today.
The early Eemian, 128 to 122 thousand years ago, coincides
with strong northern summer insolation. The top shows a
graph of ice sheet surface temperature and altitude. At the beginning of the Eemian, 128,000
years ago, the ice sheet in northwest Greenland was 200 meters higher than today, but during the warm Eemian period the ice mass regressed, so 122,000
years before now the
surface had sunk to a level of 130 meters below the
current level. During the rest of
the Eemian the ice sheet remained stable at the
same level with an ice thickness
of 2,400 meters.
(large version)
Copyright: D. Dahl-Jensen (Univ. of Copenhagen)
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Copyright Notice
The
Swiss Federal Research Institute WSL provides the artwork for imaging
of press articles relating to this media release for free. Transferring
and saving the images in image databases and saving of images by third
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A
new study provides surprising details on changes in Earth’s climate during the
last warm period (120,000-128,000 years ago). Even though temperatures in
Northern Greenland were 5-8 degrees Celsius higher than today, the thickness of
the ice sheet was only a few hundred meters lower. And this despite the fact
that sea level was 4-8 metres higher than today. This indicates that the
melting of the Greenland ice sheet may have contributed less than half of the
total sea level rise at the time. This interglacial period (the so called "Eemian")
may be a good analogue for where the Greenland ice sheet is heading today in
the face of increasing greenhouse gases and warming temperatures.
The apparent good news from this study is that the
Greenland ice sheet may not be as sensitive to temperature increases as
previously thought. However, the bad news is that if Greenland did not disgorge
larger parts of its ice into the ocean during the Eemian, then Antarctica and
here especially the more climate sensitive West Antarctic Ice Sheet must be
responsible for a significant part of the 4-8-metre sea level rise and may be
even more sensitive to climate warming than previously thought. These results
from the North Greenland Eemian Ice Drilling (NEEM) project, led by the
University of Copenhagen and with participation by the University of Bern and
Prof. Konrad Steffen, Director of the Swiss Federal Research Institute WSL, have now been published in "Nature".
The new findings also revealed temporal changes in the
higher temperatures in Northern Greenland over the last interglacial period. At
the beginning of the Eemian (128,000 years before today), the ice sheet in the
vicinity of NEEM was 200 metres higher than today. At the same time, the
temperature at the altitude of the current drill site was up to 8°C warmer.
Towards the end of the Eemian, the sheet thickness was reduced by 130 metres
compared to today but the ice was still 2400 metres thick, while the
temperature was still about 5°C warmer. The research team estimates that the
volume of the Greenland ice sheet shrank during the Eemian by no more than 25%
over 6000 years. The rate of elevation change in the early part of the Eemian
was high (about 6 cm/yr) and the loss of mass from the Greenland ice sheet was
likely on the same order as changes observed during the last ten years. "The increasing melt on
the Greenland ice sheet during the past decade and the anticipated temperature
increase of several degrees by the end of this century are indicators that the Greenland
ice sheet is expected to be a significant contributor to the sea level rise",
says Prof. Konrad Steffen, a climate specialist who has worked on the ice sheet
for the past 20 years.
The concentrations of the atmospheric greenhouse gases
methane and nitrous oxide in the Eemian, measured by the Bern team, were
similar at that time to what is observed during the preindustrial period about
150 years ago, i.e. before the increase by human emissions started. The strong
warming in Northern Greenland during the Eemian led to frequent summer melt
layers clearly recognized by a low air content and greenhouse gas
concentrations, which due to the melt processes were much higher than their
atmospheric value. Such melt events are very rare by comparison during the past
5000 years and require a warming during the Eemian of at least 4°C.
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The
NEEM project
Led by the University of Copenhagen and involving 14
nations, the team drilled an ice core to bedrock in North-West Greenland (camp
position 77.45°N 51.06°W, ice thickness about 2500 m) in just over two years.
The team extracted the first complete Greenland ice core record of the last
interglacial period, known as the Eemian. The layers in the NEEM ice core –
formed over millennia by compressed snow – are being studied in detail using a
large suite of measurements, including greenhouse gases measured by the
division of Climate and Environmental Physics at the Physics Institute of the
University of Bern. The Bern team is also measuring ionic and particulate
aerosol tracers on the NEEM ice core in very high resolution to better
understand past variations in climate on a year-by-year basis, similar in some
ways to a tree-ring record.
Prior to the NEEM project, Prof. Konrad Steffen
(WSL) installed a climate recording
station at the NEEM site to study the local conditions and thereby improve interpretation
of the ice core record. Currently, he operates a network of 20 climate stations
on the Greenland ice sheet providing evidence of environmental fluctuations for the past
20 years across this dynamic region.
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Scientific publication
- NEEM community members: Eemian interglacial reconstructed from a Greenland folded ice core, Nature,
23. Januar 2013, doi:10.1038/nature11789
Further Reading
Further information
Prof. Dr. Konrad Steffen
Swiss Federal Research Institute WSL
Zürcherstrasse 111
8903 Birmensdorf
Tel. +41 (0)44 739 24 55
