Fox Glacier and its northern neighbour Franz Josef Glacier advanced in the 1980s to 2000s because of a series of El Nino years, especially in the late 1970s to early 1980s, and again in the 1990s.
However, the past few years have been mostly La Nina weather, and as a result the glaciers had all been losing ice at a rapid rate, Dr Anderson said.
"We haven't had a good snow year on the glaciers since 2007.
"It is the same story around the world, with increasingly higher rates of ice loss from mountain glaciers," he said.
"Let's hope that the predicted El Nino does happen, because that will be good for the glaciers - but it will take more than one year to turn around the losses that we've seen in the last six or seven years, and it also takes a few years for larger snowfalls to be seen as an advance at the terminus."
In the longer term, global warming would outweigh the short-term El Nino-La Nina variations, he said.
The glaciers would still advance from time to time, but it was unlikely that they would get as long again as they were in 2008, and by 2100 "it may not even be possible to see Fox or Franz Josef glaciers from the valley floors".
The National Institute of Water and Atmosphere has given a 50 per cent chance of an El Nino developing over winter.
-The Greymouth Star
