These are admittedly daily data, and yes, it is warm in summer everywhere, and yes, when it is warm, snow and ice melt at the surface. Here is the latest image of Greenland’s warming and melting that I lifted (figure and caption) straight from today’s NASA release:
The drama comes in, when we are told, that Greenland’s ice core records from the last
“Ice cores from Summit show that melting events of this type occur about once every 150 years on average. With the last one happening in 1889, this event is right on time,” said Lora Koenig, a Goddard glaciologist and a member of the research team analyzing the satellite data. “But if we continue to observe melting events like this in upcoming years, it will be worrisome.”
We are talking a time as far back as the American Civil War, the early stages of the industrial revolution, a time when people marooned in Nares Straits starved to death because a supply ship could not reach them (Greeley’s First International Polar Year Expedition). There are cycles to all things, sure, but mathematics tells us that almost all functions (even a discontinuous step function) can be described as the sum of a large number of cycles with differing amplitudes and phases … as demonstrated by Fourier that one can read about and play with.
UPDATE 7-25: Terry Moran found ice core data and publication of Alley and Anandakrishnan (1995) that places this month’s melt into the 10,000 year context:
Basically this graph says that, averaged over the last 4000 or so, the snow melts once every 250 years at the GISP2 site. The graph also shows, that the incoming sun light (solar insulation) in July has actually decreased from 4000 years ago to today (Berger, 1979)./UPDATE
EDIT-2: Some of the current Summit, Greenland field work is conducted by PhD students and is described at Dartmouth IGERT, where IGERT stands for Integrative Graduation Education and Research Traineeship, an innovative program funded by the National Science Foundation.
Edit/Hedge: … these are daily images and all daily data that contain climate and weather and noise are always hard to interpret. The color red evokes emotions, too, but what does it represent? What are the units of the colors? How is melt defined? How does this “variable” vary as a function of time, say over 1 or 10 or 20 years? This is all very, very preliminary and, at least for me, impossible to check thoroughly.
And it only occured for a few hours §.-)
I do not know what the temporal context is, hours, days, years, decades? I do not know which remotely sensed property is actually depicted as “red.” Is it surface temperature above the freezing point (sensed in the thermal infra-red), perhaps, or something more fancy at micro-wave frequency, or some composite of all and/or more? The more fancy algorithm get, the more skeptical I get. [Removed dead link.]
I’m trying to find the url for the images similar to those that used to be provided by envisat – I’ll let you know if I succeed.
Apparently they got the 150 year figure by averaging the whole Holocene, including the warm period. The figure is probably as accurate as it is misleading.
Terry: The 150 year ago number comes from an 80-m thick ice core take at Summit, Greenland a few days ago. This 80-m core translates into a time series of annual layers that goes back to 1750 or so, e.g.,
and I see that you were already there. I am not sure it is wise to suggest a 150-year “cycle,” more likely they have one other event in 1889 that matches the 2012 melt event from a ~260 year long time series. This still is very impressive, rare, and extreme event. I personally feel much more comfortable with results derived from ice cores rather than satellite remote sensing. The fancier the “algorithm,” the more abstract the “product,” the larger the scatter, error, and sensitivity to calibrations and multiple inputs. What exactly is “melt” as sensed by satellite? Is it surface temperature above pressure-corrected freezing temperatures for fresh water or is some fancy spectral estimate on how to distinguish and count water molecules in their liquid (water) as opposed to solid phases (snow/ice)?
This gisp2 graph gives an idea of the distribution.
The green lines represent individual occurrences, and without the Holocene Warm period – they’re pretty sparse.
I think your latter supposition re water/snow/ice phase is correct, but I’m still hoping to find the new url to the data .
Thank you so much, Terry, I updated the post as this is exactly the temporal context within which to place this event, once every 250 year, if I understand Dr. Richard Alley’s graph and data correctly … averaged over the last 4000 years or so.
Andrew Revkin is covering this at the New York Times along exactly the same lines you, Terry, do. He got an aditional quote from Dr. Koenig who basically states exactly what you did earlier, Terry 😉
Thanks for the NYT link. I hope most people end up understanding how unusual the event was.
Weather Underground believes we could have a repeat as the next high pressure system moves in. I’d assume that multiple events, should they occur this close together wouldn’t be discernible in the cores.
Looking forward to your reports when you return from Nares. The new ice island is turning around, but hasn’t made a run for Hall Basin yet. Nares still looks dangerously choked with burgs.
Discerning melt using microwave data is quite straightforward given the much difference brightness temperatures of wet and dry snow. The results from NASA are from several different satellites each using different sensor types and algorithms. This leaves little doubt as to the occurrence of the melting. Hall et al (2009), provide a good overview of the NASA methodology using MODIS and Quikscat. The MODIS GIS project methods also described.
[Editor: Fixed link to Hall et al. (2009).]
I am not doubting the satellite measurements at all, but as a physicist I like to know units or have categories defined.
Neither am I doubting that this is both an extreme event that warrants attention. I do believe, however, that it should be viewed within a larger temporal context. Koni Steffen has been reporting this for years, e.g., http://cires.colorado.edu/steffen/greenland/melt2007/ where more modest “melt” is placed into temporal context. This internally consistent record strongly suggests that dramatic changes is taking place all around Greenland for several decades now (also, notice the error bars):