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).
Picture
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.
 The melting index is computed from passive microwave satellite measurements and it can be seen as a measure of the ‘strength’ of the melting season: the higher the index the more melting occurred.  With more melting yet to come during August, 2012 will position itself way above the old records, likely becoming the 'Goliath' of the melting years during the satellite record (1979 - to date).  From the map below, we see that the cumulative melting index record is due to extensive increased melting occurring all over Greenland, especially at high elevations where melting lasted up to 50-60 days longer than the average. This means that some of the areas at high elevations in south Greenland are generally subject to a few days of melting (if it happens at all) and this year they underwent melting for more than 2 months (so far). 
Picture
Map of the 2012 anomaly of the number of melting days with respect to the 1980 - 1999 average (e.g., red color indicates areas where melting lasted up to 50 days above the 1980 - 1999 mean). Updated through August 8th.
Melting was extreme also in the west, northwest and northeast regions. Along the southwest coast melting does not appear to have been extreme. However, care must be taken in interpreting the passive microwave results over this area. Indeed, the exposure of bare ice might 'blind' the microwave data and preclude them from detecting melting. Extensive bare ice (above the average for 2012 !) has been suggested by model results (e.g., see the link to Xavier Fettweis' MAR results analysis, consistently with a reduced albedo observed by satellite sensors (see post one Jason Box analysis of MODIS, as well as our papers on the role of albedo in the Scientific Literature section). In 2010, we identified in warming surface temperatures, reduced accumulation and albedo reduction (following premature exposure of bare ice) some of the major potential drivers for the melting record (see here). 
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Image Credit: Dorothy Hall (NASA/GSFC), Son Nghiem (JPL), T. Mote (Univ. of Georgia) and Marco Tedesco (CUNY)
















So, how is this record different from the one that  happened in mid July of 2012 and received so much coverage ?

The extreme melting detected at high elevations in mid July (covering ~ 97 % of the Greenland ice sheet, see image on the left) generated liquid water that refroze after a few days, changing the physical properties of the snowpack but very likely not contributing to the meltwater that run offs from the ice and can potentially contribute to sea level rise. The event was exceptional in the sense that it is a rare event (imagine a postcard of Rio de Janeiro under a thin layer of snow !) but it happened in the past, according to the research of colleagues from the Dartmouth College at Summit. The record set by the overall melting has implications on the meltwater that goes into the ocean and it can impact ice dynamics, through basal lubrication or through its impact on the subglacial and englacial drainage systems. Also, the increased melting at higher elevations might remove the seasonal snow and expose more bare ice. The removal of bare ice (which is darker and the absorb more solar radiation and it is therefore more prone to melting than snow), is actually contributing to the net mass loss of Greenland. Seasonal snow is indeed part of the annual cycle (water from the ocean goes into the atmosphere which turns into cloud and it is released as snow which melts again and goes back to the ocean) where ice has been sitting there for decades or hundreds (and more) of years and it is therefore adding new 'material' to the cycle (e.g., the ocean). 

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An important point to mention is that the passive microwave sensors cannot tell us about the amount of surface mass loss from melting. They can only 'see' when and where melting is occurring but they become 'blind' when it comes down to estimating how much water was produced from that melting. This is why we use the 'melting index', in order to have an idea of the 'strength' of the melting season. In general, there is a good correspondence between the melting index and the surface mass loss on a seasonal basis. Said this, we use models to complement the lack of information from remote sensing tools. Models have their own intrinsic limitations but they can provide estimates of physical quantities (such as the mass loss). The model we use has been widely tested vs. ground and satellite observations and we are confident about its results.  The preliminary analysis of model outputs (the Mode´le Atmosphe´rique Re´gional, a.k.a. MAR) that we obtained in collaboration with Xavier Fettweis from the University of Liege in Belgium (see link in the Main page, on the right), confirms the extreme melting year for 2012. Modeled results also indicate that the trend for the annual cumulative surface mass balance (SMB) for 2012 until the end of July is the minimum since 1958 (the model is run back to 1958, differently from satellite data that is available starting in 1979). The modeled results for the SMB until the end of July is ~ - 90 Gt (using January 1st as a starting value at zero Gt). The same values for 2010 over the same period was ~ -60 Gt and about 0 Gt for 2011. The modeled loss just for the month of August (from end of July to the end of August) in the case of 2010 was ~ - 60 Gt and it was ~ -100 Gt in the case of 2011. So, whether or not the SMB record will be set depends on how things will proceed during August. We are currenlty running the model and we might have some preliminary results by the next week. In general, we are planning to write a paper about this as soon as the season is over and we will be submitting by mid September. However it goes (whether 2012 is going to be a record or not in terms of SMB), this year will be likely be amongst the top years. Less than one month to get a response ...

Investigation is currently going on to address some of the causes of the melting record through model results and observations. The analysis of the combined remote sensing data and model outputs is carried out within the framework of a project sponsored by the National Science Foundation (NSF) to improve estimates of the surface mass balance of the Greenland ice sheet and by the NASA Cryosphere Program to collect data on ground for the validation of the results. Preliminary analysis indicates in above-normal surface temperatures and a reduction of albedo the potential major drivers for the new melting record. This is suggested by model results and other satellite observations. Let us see what August is going to reserve for us ...
 


Comments

Joe Witte
08/16/2012 10:36am

Love your site... suggest you add links to the original story sources... the link helps substantiate the academic validity of your information.
JW

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trent1492
08/17/2012 12:07am

Want to second Joe Witte. Please provide a link to the journal article.

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Maria
08/17/2012 10:11am

I think that this press release is the main source:
http://www2.ccny.cuny.edu/advancement/news/Greenland-Melting-Breaks-Record-Four-Weeks-Before-Seasons-End.cfm
(from The City College of New York)

Reply
08/17/2012 5:08pm

The Standardized Melt Index calculates a meaningless two dimensional number. A surface that melts and refreezes could possibly lose no water at all. The only meaningful number would be the three dimensional number or volume of melt water lost. Thus, the SMI is worthless.

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Marco Tedesco
08/17/2012 5:19pm

The SMI has been shown in previous studies to be correlated with the runoff. Nevertheless, we are planning to provide the overall picture of this melting season looking at the surface melting from satellite, modeled runoff and surface mass balance and ground observations of surface mass balance. This will be provided after the end of the melting season (around mid-September).

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Stephen
08/21/2012 9:00am

How do your models correlate to the estimates produced by GRACE data interpreted by Hansen?

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08/28/2012 10:43am

Hello Professor,

Do you think all this recent melting may be caused by air pollution (black carbon soot) from industrial factories in Asia and other places in the world which do not have good air quality standards?
The albedo of the glacial ice could be significantly changed by black particles which would result in more solar energy absorbed at the surface of the ice which in turn would accelerate the melting rate. Have you looked at this as a possible explanation?

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Marco
08/29/2012 6:05pm

There is no doubt that black carbon and other material (e.g. cryoconite) can play a significant role in reducing the albedo. The measurements from satellite already would include this effect (as they would look directly to what is already containing 'impurities'). However, the model does not include any parameterization of impurities in the albedo and, therefore, it does not account of the eventual changes that occurred. The changes in the albedo (e.g., reduction) that we were able to identify are mainly associated with increasing the snow grain size (as a consequence of melting refreezing cycles) and bare ice exposure. The problem with impurities non the model is to characterize their spatio-temporal distribution and insert this into the model. The albedo is relatively well known, so that wold not be a problem.

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Karl
09/27/2012 2:29am

Great to see a blog on this topic. I use NASA's Lance-Modis imagry to view Greenland. The ice loss this year revealed many new features. I think it possible for the ice sheet to become seriously destabilized by melt and possibly sea water at its base to the point where it calves a massive slab into the ocean--a piece capable of raising sea levels by a meter globally. Human induced punctuated catastorphism I believe. Seriously, much of the ice sheet will slide into the ocean rather than sit in place placidly melting. The same behavior is occuring in the west antarctic ice sheet too. Better studies of the internal stuctural physics of ice sheets warn us that such structures are not as stable as they seem.

Reply
01/23/2013 6:53am

Interesting post and thanks for sharing. Some things in here I have not thought about before.Thanks for making such a cool post which is really very well written.will be referring a lot of friends about this.
Regards,

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