Greenland Ice Sheet During the 20th Century - a Missing Link in IPCC's Climate Report

[sue4e3]

Last edited Fri Jan 8, 2016, 03:50 PM - Edit history (1)

TRACING MELTING ICE. For the very first time, climate researchers from the Centre for GeoGenetics at the Natural History Museum of Denmark, together with a national and an International team of researchers, publish in the scientific journal Nature their direct observations of the reduction and melting of the Greenland Ice Sheet during the latest 110 years. All previous estimations have been based on computer models, which although valuable do not provide the same level of insight as direct observations. In this paper, the researchers can pinpoint where the ice sheet is particularly sensitive and what controls the loss of glacier ice in Greenland. However, most importantly, the observation-based results close a gap in IPCC's estimate of global sea level budget and should be taken under strong consideration for the next IPCC convention.

The fluctuating temperatures and their effect on the Greenland Ice Sheet during the 20th Century is often a matter highly debated. One reason for this has been the lack of direct observations of the ice sheet from all of Greenland before 1992, which has made it difficult to estimate changes in both space and time during the earlier part of the twentieth century. As a direct consequense there is no contribution included from the Greenland Ice Sheet to the global sea level budget before 1990 in the United Nations climate panel's (IPCC) latest report from 2013. Concerning this lack of data, first author on the paper in Nature, postdoc Kristian K. Kjeldsen from the Centre for GeoGenetics at the Natural History Museum of Denmark at the University of Copenhagen says:

"If we do not know the contribution from all the sources that have contributed towards global sea level rise, then it is difficult to predict future global sea levels. In our paper we have used direct observations to specify the mass loss from the Greenland Ice Sheet and thereby highlight its contribution to global sea level rise".
http://www.sciencenewsline.com/news/2015121701430022.html

[muriel_volestrangler]

1. Link; unsurprisingly, ice loss is accelerating

"Our understanding of the behavior of the Greenland Ice Sheet over the last century is greatly increased, and we see that the average mass loss rate over the past decade is much larger than at any other time over the last 115 years", says co-author Associate Professor Shfaqat Abbas Khan at DTU Space, the National Space Institute at the Technical University of Denmark (DTU).

http://geogenetics.ku.dk/latest-news/alle_nyheder/2015/nature-ice-sheet/

The paper:

The response of the Greenland Ice Sheet (GIS) to changes in temperature during the twentieth century remains contentious1, largely owing to difficulties in estimating the spatial and temporal distribution of ice mass changes before 1992, when Greenland-wide observations first became available2. The only previous estimates of change during the twentieth century are based on empirical modelling3, 4, 5 and energy balance modelling6, 7. Consequently, no observation-based estimates of the contribution from the GIS to the global-mean sea level budget before 1990 are included in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change8. Here we calculate spatial ice mass loss around the entire GIS from 1900 to the present using aerial imagery from the 1980s. This allows accurate high-resolution mapping of geomorphic features related to the maximum extent of the GIS during the Little Ice Age9 at the end of the nineteenth century. We estimate the total ice mass loss and its spatial distribution for three periods: 1900–1983 (75.1 ± 29.4 gigatonnes per year), 1983–2003 (73.8 ± 40.5 gigatonnes per year), and 2003–2010 (186.4 ± 18.9 gigatonnes per year). Furthermore, using two surface mass balance models10, 11 we partition the mass balance into a term for surface mass balance (that is, total precipitation minus total sublimation minus runoff) and a dynamic term. We find that many areas currently undergoing change are identical to those that experienced considerable thinning throughout the twentieth century. We also reveal that the surface mass balance term shows a considerable decrease since 2003, whereas the dynamic term is constant over the past 110 years. Overall, our observation-based findings show that during the twentieth century the GIS contributed at least 25.0 ± 9.4 millimetres of global-mean sea level rise. Our result will help to close the twentieth-century sea level budget, which remains crucial for evaluating the reliability of models used to predict global sea level rise1, 8.

http://www.nature.com/nature/journal/v528/n7582/full/nature16183.html