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Thursday, May 8, 2014
New paper finds Greenland ice accumulation has increased 10% over past 52 years
A new paper published in the Journal of Glaciology finds that ice accumulation of the interior of Greenland has increased 10% over the past 52 years, offsetting runoff from some outlet glaciers along the periphery. According to the authors, "this implies that the increased water vapor capacity of warmer air is increasing accumulation [of ice] in the interior of Greenland."
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ReplyDeleteMore details from the paper:
http://www.dartmouth.edu/~eosterberg/images/Hawley%20et%20al,%202014%20GrIT%20radar%20accumulation.pdf
The 0.022 m w.e. a1 increase we find implies a ∼10% change in average accumulation in the dry-snow zone of the ice sheet in the past 52 years. The significance of this result is that increased accumulation, as seen on the East Antarctic ice sheet by Davis and others (2005), driven by the increased ability of warmer air to hold moisture, is also evident inland on the Greenland ice sheet. Box and others (2013) found a ∼1.2% /decade increase over the 20th century, and our result is consistent with this, if slightly higher. The significance of this for the mass balance of the Greenland ice sheet, is that at least some of the increased mass loss from melting at the lower-elevation margins of the ice sheet is balanced by the small increases in mass gain from increased accumulation in the higher-elevation interior. Comparison of our measured accumulation rates with those measured in the 1950s by Benson (1962) indicates a ∼2%/decade increase in accumulation between the periods 1945–55 and 1997–2007. Thus, due to a warmer atmosphere driving an increased capacity for moisture, and in common with the findings of Davis and others (2005) in East Antarctica, accumulation in the interior of the Greenland ice sheet has increased slightly in the currently warming climate.
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It's odd that the assumption in this paper seems to be that Greenland's ice mass (accumulation) increased because of warming---but also that it lost mass because of warming---at the same time.
Odd, too, because the temperature record in Greenland shows that it *cooled* during the 1950s to 1980s relative to the rapid warming of the 1920s to 1930s period. And the 1950s to 1980s accounted for a large portion of the 52 years of the study. So why would the authors claim the mass increases in the GIS were due to warming (warmer air holds more moisture)?
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Papers documenting a cooling GIS during the 1950s to 1980s (while CO2 levels were rapidly rising):
http://onlinelibrary.wiley.com/doi/10.1002/joc.852/abstract
Trends over the 1901–2000 century in southern Greenland indicate statistically significant spring and summer cooling. General periods of warming occurred from 1885 to 1947 and 1984 to 2001, and cooling occurred from 1955 to 1984. The standard period 1961–90 was marked by 1–2°C statistically significant cooling. Much of the observed variability is shown to be linked with the North Atlantic oscillation (NAO), sea ice extent, and volcanism.
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http://ruby.fgcu.edu/courses/twimberley/EnviroPhilo/Hanna.pdf
Analysis of new data for eight stations in coastal southern Greenland, 1958–2001, shows a significant cooling (trend-line change −1.29°C for the 44 years), as do sea-surface temperatures in the adjacent part of the Labrador Sea, in contrast to global warming (+0.53°C over the same period).
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http://link.springer.com/article/10.1023%2FB%3ACLIM.0000018509.74228.03
The Greenland coastal temperatures have followed the early 20th century global warming trend. Since 1940, however, the Greenland coastal stations data have undergone predominantly a cooling trend. At the summit of the Greenland ice sheet the summer average temperature has decreased at the rate of 2.2 °C per decade since the beginning of the measurements in 1987. This suggests that the Greenland ice sheet and coastal regions are not following the current global warming trend. A considerable and rapid warming over all of coastal Greenland occurred in the 1920s when the average annual surface air temperature rose between 2 and 4 °C in less than ten years (at some stations the increase in winter temperature was as high as 6 °C). This rapid warming, at a time when the change in anthropogenic production of greenhouse gases was well below the current level, suggests a high natural variability in the regional climate.
More papers documenting Greenland Ice Sheet growth...and its coincidence with global warming:
ReplyDelete------------------
http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00373.1
Greenland Ice Sheet Mass Balance Reconstruction. Part I: Net Snow Accumulation (1600–2009)
Over the full 410-yr period of the reconstruction, 1600–2009, a significant 12% increase (124 Gt yr) in accumulation rate is evident (Table 2). Relatively strong changes [increases] are evident, for example in the periods 1945–68 and 1968–96. There is some evidence of an increasing accumulation rate trend (an acceleration) after the trendless 1800s (Fig. 6, Table 2). The 1840–1996 trend is 30% higher than the 1600–2009 trend.
Our reconstruction suggests that since the 1600s, Greenland ice sheet accumulation rates have increased. The estimated mean accumulation rate in the most recent 170 years (1840–2009) is 30% greater than the estimated mean accumulation rate in the 410 years since 1600, suggesting an acceleration in accumulation rate.
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http://www.dartmouth.edu/~eosterberg/images/Hawley%20et%20al,%202014%20GrIT%20radar%20accumulation.pdf
The 0.022 m w.e. a1 increase we find implies a ∼10% change in average accumulation in the dry-snow zone of the ice sheet in the past 52 years. The significance of this result is that increased accumulation, as seen on the East Antarctic ice sheet by Davis and others (2005), driven by the increased ability of warmer air to hold moisture, is also evident inland on the Greenland ice sheet. Box and others (2013) found a ∼1.2% /decade increase over the 20th century, and our result is consistent with this, if slightly higher. The significance of this for the mass balance of the Greenland ice sheet, is that at least some of the increased mass loss from melting at the lower-elevation margins of the ice sheet is balanced by the small increases in mass gain from increased accumulation in the higher-elevation interior. Comparison of our measured accumulation rates with those measured in the 1950s by Benson (1962) indicates a ∼2%/decade increase in accumulation between the periods 1945–55 and 1997–2007. Thus, due to a warmer atmosphere driving an increased capacity for moisture, and in common with the findings of Davis and others (2005) in East Antarctica, accumulation in the interior of the Greenland ice sheet has increased slightly in the currently warming climate.
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http://bprc.osu.edu/Icecore/bales-jgr-1.pdf
Accumulation over the Greenland ice sheet from historical and recent records
Water accumulation, defined as precipitation minus evaporation, was estimated over all of Greenland as part of a program to understand changes in ice sheet mass and elevation. The mean length for the 256 points used was 10 years, with most of the data falling into the period 1940-present [2001 publication]. The mean accumulation was 29 g cm yr for all 256 points, and 32 g cm yr for the 17 coastal points. Recent cores [1981-2001] tend to be from higher accumulation regions (mean 32 g cm yr) than historical cores (mean 24 g cm yr); the mean value for PARCA cores is 30 g cm yr. Using kriging, the average accumulation over Greenland is estimated to be ∼30 g cm yr. For the interior part of the ice sheet above 1800 m elevation, where most of the data were acquired, the average accumulation is also estimated to be ∼30 g cm yr.
This paper shows that the surface mass loss rates on the Greenland Ice Sheet during the 1930s were higher than in recent years. Figure 5, page 122, shows no trends in surface mass balance on the GIS, if not a slight increase, in the last 100 years.
ReplyDeletehttp://www.the-cryosphere.net/2/117/2008/tc-2-117-2008.pdf
These estimates show that the high surface mass loss rates of recent years are not unprecedented in the GrIS [Greenland Ice Sheet] history of the last hundred years. The minimum SMB rate seems to have occurred earlier in the 1930s and corresponds to a zero SMB rate….The results show that the GrIS surface mass loss in the 1930s is likely to have been more significant than currently due to a combination of very warm and dry years. It is also noted from our results that a mere ten years would be enough to pass from a GrIS growth state to a significant mass-loss state. Therefore, the SMB changes that are currently occurring, and which are linked to global warming (Fettweis, 2007; Hanna et al., 2008) are not exceptional in the GrIS history.
[See figure 5, page 122, for a visual representation of the Greenland Ice Sheet’s higher surface mass loss rates trends in the 1930s compared to modern.]