For instance, the Glacier on the left doesn't seem to have lost much at all- to be fair. The one on the right seems to have lost a visible amount but given the 80 year time difference in the photos then one could be forgiven for saying they really don't demonstrate much at all... to my mind atleast!
Perhaps it doesn't look that much, but there are a few things to consider:
The images may be 80 years apart, but the retreat of the right-hand one (Helheim) didn't really start until 2001 (see http://www.climatehotmap.org/global-warming-locations/helheim-glacier-greenland.html
). So we are talking about 11 years (2001 - 2012), not 80.
The left hand glacier shows some lowering and a small retreat on the left-most side, but given the quality of the images and the distance it is very hard to quantify.
Retreat of a glacier tongue is, I believe, mostly a response to less mass behind the tongue - not how fast the ice melts at the end of the tongue. The loss of mass in the ice tongue can be very clearly seen (I've put in a few lines that show how thick the glacier tongue was at it's maximum) and, again, this thinning of the tongue is really a much stronger indicator of lesser mass and lesser pressure in the ice sheet behind than of any melting taking place in the tongue itself.
However, as I understand it, a large part of the mass being lost in the ice sheet is lost through flowing out into ice tongues such as this one and breaking off at the end, one could say that the ice is draining out to sea, and the tongues are the drain pipes. Faster flow of ice in the glacier tongues happens as a result of melting, as warmer waters melt the tongue faster and increasing melt water flows from further upstream lubricate the tongue.
But faster flow does not cause retreat (although it might cause some thinning). Both the retreat and the thinning are direct indicators of loss of mass in the ice sheet itself, and as such are of much more significance than would appear at first.