Volume 8, Number 46: 16 November 2005
The coldest period of the current interglacial or Holocene was likely the Little Ice Age, when land-based glaciers around the world achieved their maximum extensions and ice volumes. Once the planet was safely on its way to recovering from this unprecedented multi-century cold spell, however, they began to lose mass and recede. In Norway and New Zealand, "as in many other glacier regions," in the words of Chin et al. (2005), this recession was most strongly expressed in "the middle of the 20th century," which they describe as "a period of spectacular retreat as the glaciers responded to climate warming that occurred since the end of the cooler 19th century." However, as they add, "glaciers in [these] two widely separated regions have recently shown the opposite behavior towards the end of the 20th century."
In Norway, the international team of researchers reports that the main glacial retreat "ended during the late 1950s to early 1960s," and that "after some years with more or less stationary glacier front positions, [the glaciers] began to advance, accelerating in the late 1980s." Around 2000, a portion of the glaciers began to slow, while some even ceased moving; but they say that "most of the larger outlets with longer reaction times are continuing to advance." In fact, they report that "the distances regained and the duration of this recent advance episode are both far greater than any previous readvance since the Little Ice Age maximum, making the recent resurgence a significant event." Mass balance data reveal much the same thing, "especially since 1988" and "at all [western] maritime glaciers in both southern and northern Norway," where "frequent above-average winter balances are a main cause of the positive net balances at the maritime glaciers during the last few decades."
In New Zealand, equilibrium line altitude (ELA) measurements of fifty index glaciers "spread throughout the length and width of the Southern Alps" have likewise revealed "two periods of positive mass balances from 1980 to 1987 and from 1991 to 1997." The most spectacular of the resultant glacial advances was experienced by the Franz Josef Glacier, which "regained 1200 m from 1984 to 2000, an extension which recovered a significant 41% of length lost since 1900." Associated with the positive mass balance period, Chinn et al. additionally report there "has been a mean lowering of the snowline by 67 m since the 1970s."
Why have these changes occurred? "Common to both countries," in the words of Chinn et al., "the positive glacier balances are associated with increases in the strength of westerly atmospheric circulation which lowered ablation season temperatures in Norway and increased precipitation to the glaciers in both countries." How long will the new regimes persist? In Norway, the researchers write that "glaciers with longer response times continue to advance and mass balance measurements continue to be mainly positive, suggesting at least some ongoing advances during the next few years." In New Zealand, on the other hand, they say "ELA values indicate that after 2000 balances have settled to near equilibrium values." In none of the affected parts of either country, however, has there been a return to significant glacier wastage.
It is interesting to note, in this regard, that at the apex of a global warming that has been characterized as the greatest of the past two millennia (Mann and Jones, 2003), maritime glaciers at these two ends of the world have not been wasting away, just as the Greenland Ice Sheet has also not been wasting away (see our Editorial of 2 Nov 2005). Indeed, all of these huge land-based repositories of ice have been experiencing a phenomenal period of growth.
Sherwood, Keith and Craig Idso
References
Chinn, T., Winkler, S., Salinger, M.J. and Haakensen, N. 2005. Recent glacier advances in Norway and New Zealand: A comparison of their glaciological and meteorological causes. Geografiska Annaler 87 A: 141-157.
Mann, M.E. and Jones, P.D. 2003. Global surface temperatures over the past two millennia. Geophysical Research Letters 30: 10.1029/2003GL017814.