Wednesday, January 23, 2013

New paper finds Greenland was much warmer in the past & is less vulnerable to thaw than previously thought

A new paper published in Nature finds from ice cores that Greenland was 8C warmer than the present during the last interglacial period from 130,000 to 115,000 years ago. The authors also find "only a modest ice-sheet response to the strong warming," during which the ice sheet was 130 meters lower than the present. Needless to say, no "tipping point" occurred when Greenland warmed by more than 2C, as claimed by climate alarmists.

Greenland ice cores reveal warm climate of the past

 IMAGE: The NEEM ice core drilling project in northwest Greenland is an international project led by the Centre for Ice and Climate at the Niels Bohr Institute. For four years the...
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In the period between 130,000 and 115,000 years ago, Earth's climate was warmer than today. But how much warmer was it and what did the warming do to global sea levels? – as we face global warming in the future, the answer to these questions is becoming very important. New research from the NEEM ice core drilling project in Greenland shows that the period was warmer than previously thought. The international research project is led by researchers from the Niels Bohr Institute and the very important results are published in the prestigious scientific journal, Nature.

In the last millions years the Earth's climate has alternated between ice ages lasting about 100,000 years and interglacial periods of 10,000 to 15,000 years. The new results from the NEEM ice core drilling project in northwest Greenland, led by the Niels Bohr Institute at the University of Copenhagen show that the climate in Greenland was around 8 degrees C warmer than today during the last interglacial period, the Eemian period, 130,000 to 115,000 thousand years ago.

"Even though the warm Eemian period was a period when the oceans were four to eight meters higher than today, the ice sheet in northwest Greenland was only a few hundred meters lower than the current level, which indicates that the contribution from the Greenland ice sheet was less than half the total sea-level rise during that period," says Dorthe Dahl-Jensen, Professor at the Niels Bohr Institute, University of Copenhagen, and leader of the NEEM-project.

Past reveals knowledge about the climate

The North Greenland Eemian Ice Drilling project or NEEM, led by the Niels Bohr Institute, is an international project with participants from 14 countries. After four years of deep drilling, the team has drilled ice cores through the more than 2.5 kilometer thick ice sheet. The ice is a stack of layer upon layer of annual snow fall which never melts away, and as the layers gradually sink, the snow is compresses into ice. This gives thousands of annual ice layers that, like tree rings, can tell us about variations in past climate from year to year.
The ice cores are examined in laboratories with a series of analyses that reveal past climate. The content of the heavy oxygen isotope O18 in the ice cores tells us about the temperature in clouds when the snow fell, and thus of the climate of the past. The air bubbles in the ice are also examined. The air bubbles are samples of the ancient atmosphere encased in the ice and they provide knowledge about the air composition of the atmosphere during past climates.

 IMAGE: The climate graph shows the temperature from the previous warm interglacial period, the Eemian (left) throughout the entire ice age to present time. The blue colours indicate ice from a...
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Past global warming

The researchers have obtained the first complete ice core record from the entire previous interglacial period, the Eemian, and with the detailed studies have been able to recreate the annual temperatures – almost 130,000 years back in time.
"It is a great achievement for science to collect and combine so many measurements on the ice core and reconstruct past climate history. The new findings show higher temperatures in northern Greenland during the Eemian than current climate models have estimated," says Professor Dorthe Dahl-Jensen, Niels Bohr Institute.

Intense melting on the surface

During the warm Eemian period, there was intense surface melting that can be seen in the ice core as layers of refrozen meltwater. Meltwater from the surface had penetrated down into the underlying snow, where it once again froze into ice. Such surface melting has occurred very rarely in the last 5,000 years, but the team observed such a melting during the summer of 2012 when they were in Greenland.

"We were completely shocked by the warm surface temperatures at the NEEM camp in July 2012," says Professor Dorthe Dahl-Jensen. "It was even raining and just like in the Eemian, the meltwater formed refrozen layers of ice under the surface. Although it was an extreme event the current warming over Greenland makes surface melting more likely and the warming that is predicted to occur over the next 50-100 years will potentially have Eemian-like climatic conditions," she believes.

Good news and bad news

During the warm Eemian period there was increased melting at the edge of the ice sheet and the dynamic flow of the entire ice mass caused the ice sheet to lose mass and it was reduced in height. The ice mass was shrinking at a very high rate of 6 cm per year. But despite the warm temperatures, the ice sheet did not disappear and the research team estimates that the volume of the ice sheet was not reduced by more than 25 percent during the warmest 6,000 years of the Eemian.

"The good news from this study is that the Greenland ice sheet is not as sensitive to temperature increases and to ice melting and running out to sea in warm climate periods like the Eemian,as we thought" explains Dorthe Dahl-Jensen and adds that the bad news is that if Greenland's ice did not disappear during the Eemian then Antarctica must be responsible for a significant portion of the 4-8 meter rise in sea levels that we know occurred during the Eemian.

This new knowledge about past warm climates may help to clarify what is in store for us now that we are facing a global warming.
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Niels Bohr Institute: http://www.nbi.ku.dk/english/


see also:

Greenland ice less vulnerable than feared to thaw: study

By Environment Correspondent Alister Doyle

OSLO | Wed Jan 23, 2013 2:34pm EST

(Reuters) - Greenland is less vulnerable than expected to a runaway melt that would drive up world sea levels, according to scientists who found that only a quarter of the ice sheet thawed in a warm period more than 100,000 years ago.

Paper shows a change in insolation of 60 Wm-2, which results in [60-30% albedo] = 10.5 Wm-2 annualized solar forcing at the surface caused about 15C temperature change, or 1.4 C/Wm-2, which is essentially the same solar forcing observed over the 20th century.


Nature
 
493,
 
489–494
 
(24 January 2013)
 
doi:10.1038/nature11789
Received
 
Accepted
 
Published online
 
Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling (‘NEEM’) ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8±4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400±250 metres, reaching surface elevations 122,000 years ago of 130±300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.

3 comments:

  1. http://www.clim-past-discuss.net/9/3711/2013/cpd-9-3711-2013.html

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  2. http://www.kaltesonne.de/?p=13546

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  3. http://stevengoddard.wordpress.com/2013/10/17/shock-news-greenland-has-been-cooling-for-70-years/

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