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.
NOAA today posted the following focusing on melting at Summit during the month of July 2012.
Here's the full link:
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.
Here's a message that Chris Shuman from UMBC/NASA Goddard posted on cryolist concerning the Summit Greenland temperatures. I am also attaching an updated figure from Chris showing that temperatures at Summit reached high values again over the past few days. I quickly looked at satellite data and though I could not see any melting for those days, the area undergoing melting was going up again. I will post an update later.
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.
Considering the large coverage of the news of the large melt extent over Greenland reported by NASA, I thought it would be helpful to report some of the previously detected melt extent 'anomalies'.
The melt extent observed during July 2012 is unprecedented (during the satellite era, 1979 - to date) but I can recall at least two cases (one in Greenland and one in Antarctica) when melt extent was out of the ordinary.
Map of annual melting indeces from satellite microwave data for the period 1979 - 2011
The image on the left shows a different way to visualize the melting index obtained from spaceborne microwave remote sensing data. The size of the fonts for each year is proportional to the rank of the year in terms of melting index (e.g., the bigger the font the stronger the melting). Colors complement the size of the fonts and indicate by how many standard deviations that particular year was above (red color) or below (blue color) the average. Note that the color scale is not linear. Feel free to use the image for presentations, talks or anything that might be helpful to you. I would appreciate to be contacted to know where the image has been used for. High-resolution version is available upon request. In any case, please credit M. Tedesco.
Year 2011 Greenland melting remains well above the (1979 – 2010) average; close-to-record mass loss
Melting in Greenland in 2011 was still above the average (1979 – 2010 baseline period), exceptionally high over the west coast and reaching close-to-record simulated surface mass balance, bare ice exposure, albedo and runoff anomalies. See here for more details or go to http://greenland2011.cryocity.org