New data for 2014 concerning the retreat of the calving front of the Jakobshavn glacier, Greenland, on the NASA Earth Observatory site.
I am re-posting an interesting message from Mauri Pelto on the Zachariae Isstrom ice loss. The original message is below ....
Dear Glacier Colleagues:
Petermann has got lots of attention this summer but the losses in area of Zachariae Isstrom and the open water currently at its front are worth noting. Below is a link to a post on the glacier with numerous Landsat images, this is meant only as a visual update not a substitute for the detailed research that has been conducted and will continue on this important outlet glacier.
Melting in Greenland set a new record before the end of the melting season. Over the past days, the cumulative melting index over the entire Greenland ice sheet (defined as the number of days when melting occurs times the area subject to melting) on August 8th exceeded the record value recently set in 2010 for the whole melting season (which usually ends around the beginning or mid September).
Standardized melting index (SMI) for the period 1979 - 2012. the years between 1979 and 2011 use the full length season (May through September) where 2012 uses only the available period May through August 8th. Note that 2012 value is much higher than any of the previous years, despite the shorter period.
Here's a link to Jason Box 2012 analysis of albedo over the Greenland ice sheet. The reduction of the albedo is a critical factor for enhancing melting over the Greenland ice sheet. The image on the left shows the ice sheet albedo time series updated through July 2012 by Jason Box.
To better understand the importance of this mechanism you can check a recently published paper on the Cryosphere Discussion by Box et al. (2012) in which we focus on this problem or another paper (Tedesco et al., 2011) that we published on Environmental Research Letters focusing on the role of albedo and accumulation on the 2010 melting recording in Greenland. Both papers are also available in the Scientific Literature section of this site.
The plot below shows the passive microwave brightness temperature time series over Summit recorded between 1979 and 2011 (the ensemble of gray lines) and the time series recorded during 2012 (black thick line). The ensemble clearly shows that things are relatively stable at Summit, with relatively small interannual variability.
The recently observed melt extent record over Greenland has shown the capabilities of remote sensing data to monitor large areas on a daily basis. The melting observed at high elevations over Greenland did not generate meltwater that contributed (or could have contributed) directly to sea level rise, mainly because liquid water refroze after the event, creating the ice layer that has been used to confirm the event. The same remote sensing tools are used to observe melting at lower elevations, where it happens every summer. Here, meltwater can either directly contribute to SLR or it can impact ice sheet dynamics, modulating the ice velocity and shaping the evolution of the englacial summer system of channels through which meltwater flows (see this video, for example). Over the past years, surface melting over Greenland has been increasing, setting new a new record in 2010 and a close-to-record melting season in 2011.
So, what happened in 2012 over the rest of Greenland while the warm air was climbing up Summit ?
The graph below shows the Standardized Melting Index (SMI, obtained from the melting index by subtracting the mean for the period 1979 - 2012 and dividing by the standard deviation for the same period) for the period June 1st - July 20th. Values above 0 indicate those cases when melting was above the 1979 - 2012 mean. For the period when data is available, therefore, the SMI set a new record for the satellite era.