Regional cooling caused recent New Zealand glacier advances in a period of global warming

Abstract

Glaciers experienced worldwide retreat during the twentieth and early twenty first centuries, and the negative trend in global glacier mass balance since the early 1990s is predominantly a response to anthropogenic climate warming. The exceptional terminus advance of some glaciers during recent global warming is thought to relate to locally specific climate conditions, such as increased precipitation. In New Zealand, at least 58 glaciers advanced between 1983 and 2008, and Franz Josef and Fox glaciers advanced nearly continuously during this time. Here we show that the glacier advance phase resulted predominantly from discrete periods of reduced air temperature, rather than increased precipitation. The lower temperatures were associated with anomalous southerly winds and low sea surface temperature in the Tasman Sea region. These conditions result from variability in the structure of the extratropical atmospheric circulation over the South Pacific. While this sequence of climate variability and its effect on New Zealand glaciers is unusual on a global scale, it remains consistent with a climate system that is being modified by humans.

Velocity increases at Cook Glacier, East Antarctica linked to ice shelf loss and a subglacial flood event

“…New Zealand occurred around the 1940s; this retreat continued at varying rates until the 1990s, when glaciers advanced in response to regional cooling (Mackintosh et al, 2017). A similar trend is seen in the Cook-Ninnis-Mertz region; along with Cook West (Fig.…”

“…Zealand's glaciers, whereby large-scale atmospheric waves connect the two regions (Crespin et al, 2014;Mackintosh et al, 2017). The onset of the rapid retreat of mountain glaciers in…”

The Influence of Weather Systems in Controlling Mass Balance in the Southern Alps of New Zealand

“…The 2010/2011 summer is ranked as one of the five strongest La Niña events on record and was until 2017/2018 responsible for the most negative mass balance at Brewster Glacier (Cullen et al, ). The similarity between the pressure anomalies suggests there is a coherency and structure to the atmospheric conditions controlling mass balance over a range of temporal scales, ranging from days to weeks as controlled by weather system or synoptic‐scale processes (e.g., Gillett & Cullen, ; Hay & Fitzharris, ), through to interannual to decadal time scales as controlled by regional‐ to global‐scale ocean‐atmosphere phenomena (e.g., Clare et al, ; Fitzharris et al, , ; Mackintosh et al, ; Tyson et al, ).…”

“…The Southern Alps are surrounded by vast areas of ocean and are strongly influenced by both subtropical and polar air masses, with the interaction of these contrasting air masses in the prevailing westerly airflow having a strong influence on glacier mass balance (Fitzharris et al, , ). Changes in large‐scale atmospheric circulation in the Southern Hemisphere are capable of temporarily countering the effects of global warming, as demonstrated by the advance of some of the fast‐responding glaciers in the Southern Alps of New Zealand at the end of the 20th and beginning of the 21st century during three of the warmest decades of the instrumental era (Mackintosh et al, ). Despite the advance of more than 50 glaciers during this period, it did not prevent the volume of ice contained in the Southern Alps from decreasing (Chinn et al, ), as the largest debris‐covered glaciers in the Southern Alps (e.g., Tasman Glacier), which account for about half of New Zealand's total glacier volume, continued to retreat.…”

“…Not surprisingly, understanding the linkages between large‐scale atmospheric circulation and glacier behavior in the Southern Alps has been a central issue for glaciologists and climatologists in New Zealand for decades (e.g., Chinn et al, ; Clare et al, ; Fitzharris et al, , ; Hay & Fitzharris, ; Hooker & Fitzharris, 1992; Mackintosh et al, ; Salinger et al, ; Tyson et al, ). Although glaciers are sensitive to atmospheric processes operating across a hierarchy of spatial and temporal scales, air temperature plays a governing role in controlling mass balance variability in the Southern Alps (e.g., Anderson et al, ; Anderson & Mackintosh, ; Chinn et al, ; Mackintosh et al, ; Oerlemans, ), in particular the air temperature associated with moisture‐bearing air masses (Conway & Cullen, ).…”