Many skeptics will point to the expanding Greenland ice as proof that global warming isn't happening.  This misleading argument can be seen by Richard Lindzen in the Boston.com article "MIT's inconvenient scientist":

`the evidence so far suggests that the Greenland ice sheet is actually growing on average," and ``Alpine glaciers have been retreating since the early 19th century, and were advancing for several centuries before that. Since about 1970, many of the glaciers have stopped retreating and some are now advancing again. And, frankly, we don't know why."

The truth is that overall ice mass is way down.  This is obvious if you simply look at the changes in the north poles ice cap:

North Pole Ice: Summer 1979 vs Current	Global Glacier Mass
	source: NSIDC

70 out of 81 of the glaciers monitored by the World Glacier Monitoring Service are shrinking.  And overall ice mass balance is way down.  So why is Greenland growing?  The quick and dirty answer is that Greenland is melting faster.  However, the warmer ocean temperatures are changing the snow and rain patterns around the world.  Greenland has seen a significant increase in snow.  This extra snow is outpacing the increased melt.   If current trends continue, it is only a matter of time before this trend reverses.  

Glaciers around the world are melting at a dramatically increased rate.  When an icesheet starts melting faster a few of the things you will see are:

• far more icebergs breaking off
• an increase in both the frequency and strength of streams and rivers carrying water off of the ice
• a thinning of the ice around the edges of the sheet

All of these phenomina (and more) are occuring on the Greenland ice sheet.  Since 1979 the area of the Greenland ice sheet that is melting (melting occurs at the edges) has increased by 16% which means it's losing about 46 cubic kilometers of ice a year.  Yet the interior of greenland is gaining about 11 gigatons of snow a year.  This difference between these two numbers means greenland is gaining about 11 gigatons of snow/ice a year.  So Lindzens comment about "we don't know why" is a little misleading.


More information:

• Grist Mill: Glaciers have always grown and receded
• Greenland Melt Extent, 2005
• Hanna et al, 2005 - Runoff and mass balance of the Greenland ice sheet: 1958–2003
• Journal of Glaciology - Zwally et al. (2005)
• Johannessen et al., 2005 - Recent Ice-Sheet Growth in the Interior of Greenland  (snow accumulation tracking)
• Rignot & Kanagaratnam, 2006 - Changes in the Velocity Structure of the Greenland Ice Sheet
• Realclimate.org - The Greenland Ice
• National Snow and Ice Data Center: State of the Cryosphere
• worldwide glacier retreat
• IPCC: gloabl glacier stats
• NASA Sees Rapid Changes in Arctic Sea Ice (14% reduction in perennial ice)

Observation equipment

• Ground: Automatic Weather Stations
• Gravity Recovery and Climate Experiment (GRACE)
• Ice cores
• European Remote-Sensing Satellites
• and much more

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