The Ice Load of Jan Mayan Island
Rolstad Denby, C. and Hulth, J. 2011. Assessment of differentiated surface elevation data from 1949, 1975 and 2008 for estimates of ice-volume changes at Jan Mayen. Journal of Glaciology 57: 976-980.
Working with geodetic data derived from optical images of the island obtained in 1949, 1975 and 2008, the authors were able to provide initial information on ice-volume changes there over the past six decades.
Specifically, the two researchers from the Norwegian University of Life Sciences report that, over the 33-year period 1975-2008, the ice volume in the southern part of Jan Mayen Island definitely increased; and they add that the data suggest that there was also an increase in ice volume in this area over the 59-year period 1949-2008, although the latter result was not statistically significant. So how is it that the island's ice load grew, especially when the annual mean temperature of the region rose by 1.58°C over the last thirty years?
Rolstad Denby and Hulth note that "from the 1960s to the 1980s, sea-ice surrounding the island was observed during winter (Orheim, 1993)," but they say that "the sea-ice has now retreated in response to the sizable regional warming." And with greater evaporation and a concomitant winter precipitation increase of 7%, they write that "the increase in ice volume in the southern parts may be explained by orographic effects on precipitation, as well as possible changes in winter precipitation patterns due to the observed retreat of the sea-ice cover."
In coastal regions where warming causes winter sea-ice to no longer form, the extra moisture thus made available to the local atmosphere by nearby evaporation can sometimes enhance the delivery of precipitation (in the form of snowfall) to the land; and this phenomenon can lead to a buildup of glacial mass, even in a warming environment, as demonstrated by the Jan Mayen experience.
Orheim, O. 1993. Glaciers of Jan Mayen, Norway. In: Williams Jr., R.S. and Ferrigno, J. (Eds.). Satellite Image Atlas of Glaciers of the World. U.S. Geological Survey Professional Paper 1386-E, U.S. Geological Survey, Denver, Colorado, USA.