it only takes a couple of degree's to change the earth from being cold, to becoming an iceball. Or, going the other direction in temperature , a tolerance of a couple of degree's that drives extinction events.
Joey, you have nailed it there!
This marked retreat of the Tasman and other of New Zealand's glaciers has occurred in less than 20 years, during which the country's average temperature has increased by 0.3 degrees Celsius (when compared with the thirty year average temperatures 1961-1990).
i.e. A temperature increase of not even one third of a degree Celsius has been enough to remove long lengths from what once were large glaciers, and leave in each place a terminal lake.
(New Zealand's thirty year average temperature 1961 to 1990 was 12.47 deg.C. The country's average over the seventeen years 2000 to 2016 - while this rapid glacial retreat has taken place - is 12.77 deg.C)
For anybody that is interested, this data can be found via the following link