Comment on tc-2023-55

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> Over the last century, northwestern Canada experienced some of the highest rates of tropospheric warming globally, which caused glaciers in the region to rapidly retreat. Our study seeks to extend the record of glacier fluctuations and assess climate drivers prior to the instrumental record in the Mackenzie and Selwyn Mountains of northwestern Canada. We collected 27 ¹⁰Be surface exposure ages across nine cirque and valley glacier moraines to constrain the timing of their emplacement. Cirque and valley glaciers in this region reached their greatest Holocene extents in the latter half of the Little Ice Age (1600&ndash;1850 CE). Four erratics, 10&ndash;250 m distal from late Holocene moraines, yielded ¹⁰Be exposure ages of 10.9&ndash;11.6 ka, demonstrating that by ca. 11 ka, alpine glaciers were no more extensive than during the last several hundred years. Estimated temperature change obtained through reconstruction of equilibrium line altitudes show that since ca. 1850 CE, mean annual temperatures rose 0.2&ndash;2.3 &deg;C. We use our glacier chronology and the Open Global Glacier Model (OGGM) to estimate that since 850 CE, glaciers in this region reached a maximum total volume of 34&ndash;38 km³ between 1765&ndash;1855 CE and have lost nearly half their ice volume by 2019 CE. OGGM was unable to produce modeled glacier lengths that match the timing or magnitude of the maximum glacier extent indicated by the ¹⁰Be chronology. However, when applied to the entire Mackenzie and Selwyn Mountain region, past-millennium OGGM simulations using the Max Planck Institute Earth System Model (MPI-ESM) and the Community Climate System Model 4 (CCSM4) yield late Holocene glacier volume change temporally consistent with our moraine and remote sensing record, while the Meteorological Research Institute Earth System Model 2 (MRI-ESM2) and the Model for Interdisciplinary Research on Climate (MIROC) fail to produce modeled glacier change consistent with our glacier chronology. Finally, OGGM forced by future climate projections under varying greenhouse gas emissions scenarios predict 85 to over 97 % glacier volume loss by the end of the 21st century. The loss of glaciers from this region will have profound impacts to local ecosystems and communities that rely on meltwaters from glacierized catchments.