Global warming: Ice core reveals climate change in Greenland’s past

January 30, 2016

Nuuk (Bernd F. Laeschke – January 2013): The last great warming period dates back more than 120,000 years ago, Ice cores drilled in the Greenland ice sheet show. The Eemian period, which began about 130,000 years ago and lasted about 16,000 years, is referred to as the last interglacial. It was a time when warm temperatures dominated the climate, due mainly to the earth’s orbit allowing more energy to be received from the sun. The world today is considered to be in an interglacial period called Holocene that has lasted 11,000 years.

Scientists have used a 2,540 meter long Greenland ice core to reach back to the Eemian period 115-130 thousand years ago and reconstruct the Greenland temperature and ice sheet extent back through the last interglacial. This period is likely to be comparable in several ways to climatic conditions in the future, especially the mean global surface temperature, but without anthropogenic or human influence on the atmospheric composition. At the peak of the Eemian, the northern hemisphere winters were warmer and wetter than today in most areas.

"The ice is an archive of past climate and analysis of the core is giving us pointers to the future when the world is likely to be warmer", says Dr. Mauro Rubino, a scientist working at Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO). He says the Greenland ice sheet is presently losing mass more quickly than the Antarctic ice sheet. Of particular interest is the extent of the Greenland continental ice sheet at the time of the last interglacial and its contribution to global sea level.

Deciphering the ice core archive proved especially difficult for ice layers formed during the last interglacial because, being close to bedrock, the pressure and friction due to ice movement impacted and re-arranged the ice layering. These deep layers were “re-assembled” in their original sequence using careful analysis, particularly of concentrations of trace gases that tie the dating to the more reliable Antarctic ice core records.

Using dating techniques and analyzing the water stable isotopes, the scientists estimated the warmest Greenland surface temperatures during the interglacial period about 130,000 years ago were about 8 degrees Centigrade (14.4 degrees Fahrenheit) warmer than the average of the last 1,000 years. At the same time, the thickness of the Greenland ice sheet decreased by about 400 meters, or less than 25 percent of its volume. However, scientists say that the loss in thickness could have been as little as 150 meters or as much as 650 meters.

“The findings show a modest response of the Greenland ice sheet to the significant warming in the early Eemian and lead to the deduction that Antarctica must have contributed significantly to the 6 meter higher Eemian sea levels”. Additionally, ice core data at the drilling site reveal frequent melt of the ice sheet surface during the Eemian period. “During the exceptional heat over Greenland in July 2012 melt layers formed at the site. With additional warming, surface melt might become more common in the future,” the authors of the study said.