Figure 7: Climate anomalies for glacier mass gain and loss.

Composite patterns for upper (gain) and lower (loss) quintiles of Southern Alps glacier mass balance changes (Supplementary Table 4), for (a) 1,000 hPa geopotential height (analogous to atmospheric pressure near mean sea level) anomalies (z1000), (b) SST anomalies (SSTa), and (c) precipitable water content (PWC) anomalies. Glacier mass gain over cool and warm seasons, as well as the glacier year, is associated with low atmospheric height/pressure, low SST in the Tasman Sea, and slightly higher precipitation, especially in summer when it is less effective. Glacier mass loss is associated with high atmospheric height/pressure and high SST. The bottom panel (d) is a schematic diagram indicating significant differences in means (P<0.05) for climate indices associated with glacier mass gains and losses. We assessed whether the index favoured glacier mass loss (brown), gain (blue), or both (green) by examining the differences of means (absolute values and sign, Supplementary Table 5). If the difference of means were of approximately the same magnitude and opposite sign for gain and loss, then the index (and mass balance driver) was considered important for both. If an absolute magnitude of a mean index value exceeded its counterpart by a factor of two or more, then that index (and mass balance driver) was considered more important for either gain or loss. Regional climate indices and drivers shown include Tasman SST, Southern Oscillation Index (SOI), T synoptic type (‘T’ type), Pacific South American pattern and Zonal Wave 3 (ZW3). Tasman SST has the strongest and most persistent association with glacier volume changes in the Southern Alps (see Supplementary Fig. 7).