Apparently NASA should start distributing dictionaries to the authors of its press releases.
 
Here is the title of the July 24, 2012 NASA press release reporting on recent ice melt across the surface of Greenland:

"Satellites See Unprecedented Greenland Ice Sheet Surface Melt"

And here is a quote from within the release:

"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," says Lora Koenig, a Goddard glaciologist and a member of the research team analyzing the satellite data.

Now, according to our version of Webster's New Collegiate Dictionary, "unprecedented" is defined as:

"having no precedent: NOVEL, UNEXAMPLED"

Dictionary.com concurs:

"without previous instance; never before known or experienced; unexampled or unparalleled: an unprecedented event."

So, while it may be meteorologically interesting that a series of high pressure ridges had passed over Greenland this summer with largest and warmest of these parking over the island for a few days in mid-July and raising the temperature to near the melting point of ice all the way up to the summit of Greenland's ice cap-it is not a type of event which is unique. Rare perhaps, but not unprecedented.