Changes in surface mass balance and summer temperature from 1961–1990 to 1991–2020 for 37 glaciers with long records

Abstract

Recent satellite measurements of glacier mass balance show mountain glaciers all over the world had generally negative mass balances in the first decades of the 21st century. We analyse archived data for surface mass balance and summer temperature for 37 Northern Hemisphere glaciers with data for 1961–2020. We compare mean annual balances for 1961–90 and 1991–2020, and for 25 glaciers explain the changes in annual balance by changes in winter and summer balances. Mean balances 1961–90 were already substantially negative for 19 out of the 25 glaciers. Changes in winter balances from 1961–90 to 1991–2020 average close to zero but changes in summer balance are strongly negative. Mean balance 1991–2020 is strongly correlated with change in summer balance, weakly correlated with winter balance change, and strongly correlated with mean balance 1961–90. We estimate 1991–2020 summer temperature anomalies for the 37 glaciers and confirm that summer temperature anomalies for 1991–2020 were higher for the Alps, by nearly 1.5°C, than for other areas. Substantial variations in the temperature – sensitivity of summer balances for individual glaciers of −0.2 to −1.0 m w.e. a−1 °C−1 deserve further study.

Visualizing Changes in Global Glacier Surface Mass Balances before and after 1990

“…The largest warming (1-2 • C) was in central Europe, including the Alps, the Mediterranean and in the Middle East, while temperature rises were 0-1 • C in other areas where glaciers occur. Glacier melting depends on summer temperatures [9,10], so Figure 1 supports the assertion that the negative mass balances of the early 21st century are due to rising temperatures.…”

“…In the present paper we discuss the data regarding glacier surface mass balances in Braithwaite and Hughes [10], which include an extensive and critical review of such data and we do not need to repeat this here, although a few comments are needed.…”

“…Surface balance measurements are only available from a few hundred glaciers. See Figure 1 in [10]. As an alternative to the laborious field work, mass balances can now be measured from satellites [17,18].…”

“…We encourage readers to browse the WGMS database [28] to check that their data are included. Figure 1 in [10] shows the length of mass balance records up to 2020 from 482 glaciers in the WGMS database [28]. Two very long records are for Swiss rescue data [29,30], but most of the records are very short.…”

“…Glaciologists do not always measure winter and summer balances, even when applicable, for reasons of logistics and/or economy. Table 1 in [10] notes the greatly expanded network for 1961-2020, with more than half the available records (58%) in the last three decades . For the present study, therefore, we compare mass balances for the past two 30-year periods.…”