Dynamic of glacier retreat? (here: in Greenland)

During the last years I have taken many pictures of obviously retreating glaciers and empty moraines in Greenland – just like this one. Looks devastating, actually.
In my understanding, the current retreat of the glaciers is due to anthropogenic climate change.

(Picture taken about 500 km north of the polar circle on the Nussuaq peninsular, Greenland, August 2019)

When I have a look at the satellite image (screenshot from google earth) of 2016, the size of the glacier tongues seems plausible.

Looking at the satellite image from 1984 (it’s also a screenshot from google earth), it irritates me that the differences in glacier extent in the satellite images seem to be relatively small.
Of course I know that the loss of mass of the ice is not only reflected in the shrinking area but also in the reduced thickness of the ice. What still irritates me is the fact that a massive retreat of the ice must have taken place before 1984.

Local Greenlandic people told me that only a few generations ago, these glacier tongues were driven by dog sleds to go from valley to valley in winter when the sea was frozen over. That would not be possible today.

Now I ask myself:

• are the satellite images from 1984 faulty?
• Did the essential retreat of the ice take place in the years of industrialization before 1984?
• Or did this retreat take place over a longer period of time in the history of the earth ("since the last ice age")?

Thank you in advance for sharing your thoughts on this!

PS: I’ve discovered the picture from 1984 via this time-travel function in Google Earth (Pro). I think the month (12) isn’t correct because in winter there should be more snow visible. Maybe the month just isn’t specified because all older pictures seem to default to December.