Description: Concurrent with atmospheric warming, glaciers around the world are rapidly retreating affecting global sea level and streamflow. Projections show considerable mass losses over the 21st century, however, mass losses vary strongly between regions and emission scenarios. In some regions with relatively little ice cover projections driven by high emission scenarios show near-complete deglaciation by the end of this century, while in polar regions relative mass losses are typically in the order of a few tenths of percent relative to the present. The mass losses modify local runoff regimes and lead to increases in glacier runoff in some regions but to decreases in others. Projected global glacier mass losses by the end of the 21st century correlate linearly with global mean temperature increase indicating that reducing global warming will limit future mass losses and their impacts.

Description: Anthropogenic contribution to global glacier mass loss started to be clearly detectable at the latest in the second half of the 20th century, but greenhouse gas emissions started earlier. Apart from natural variability masking the anthropogenic signal, the delayed detection in glacier mass loss is caused by the long response time of glaciers to climate change. This implies that emissions do not only have an impact on glacier mass loss when they occur, but also far beyond. Here, we present an approach designed to quantify the temporally accumulated contribution of past emissions to past and future glacier mass loss. Using the simple climate model FaIR (Finite Amplitude Impulse Response), we converted the emission pathway of single emitters (e.g., countries) to their yearly contribution to the global mean temperature anomaly. In order to quantify the delayed glacier response, we performed idealized experiments with OGGM (Open Global Glacier Model), taking into account the spatial distribution of temperature and precipitation anomalies. This allows us to estimate a time series of glacier mass change resulting from a specified time series of global mean temperature change, such that we can link arbitrary emissions in a given year to a corresponding time series of glacier mass loss. In a first attempt, we applied our method to all glaciers of the Alps, and forced our simulations with the CMIP6 “historical” data set using 13 different GCMs. In this way, we were able to allocate country-specific responsibilities for past and future glacier mass loss in the Alps.

Description: Glaciers outside the ice sheets are major contributors to current sea-level rise and are projected to remain so in the coming century. At regional scales, glaciers are important natural freshwater resources that provide water to populations in downstream areas. To assess these important roles and to better quantify the impacts arising from changing glaciers, the Glacier Model Intercomparison Project (GlacierMIP) has developed a set of coordinated experiments. The third phase of the Glacier Model Intercomparison Project (GlacierMIP3) focuses on the equilibration of glaciers under constant climatic conditions. More specifically, GlacierMIP3 aims to answer the following three fundamental questions:1) What would be the equilibrium volume and area of all glaciers outside ice sheets if global mean temperatures stabilized at present-day levels?2) What would be the equilibrium volume and area of all glaciers outside ice sheets if global mean temperatures stabilized at different temperature levels (e.g. +1.5°C, +2°C relative to pre-industrial)?3) For each of these global mean temperature stabilization scenarios, how much time would the glaciers need to reach their new equilibrium?In this contribution, we present the first results from GlacierMIP3. We focus on the global stabilization of glaciers under various temperature levels, and thereby also highlight how regional differences can be linked to glacier characteristics and regional climatic warming trends.

Description: The ocean mass budget plays a crucial role in predicting future changes in ocean mass and sea level. In recent efforts to reconcile observations from GRACE and GRACE-Follow On satellites with steric-corrected altimetry and models of contributions from land and ice a discrepancy in the mass budget has been reported (Wang et al, 2022; Barnoud et al, 2022), in particular in the period following the launch of GRACE-Follow On. In this study, we aim to compare 20 years of GRACE-observed mass changes with steric-corrected altimetry and GRD-induced sea level changes resulting from landmass changes. To accomplish this, we produce monthly 3D global mass change products with a spatial resolution of 0.5 degrees, covering the period from 2003 to 2022. We improve the processing steps for steric-corrected satellite altimetry by accounting for ocean bottom deformation, removing the global mean contribution of halosteric sea level change, and replacing the radiometer-based wet tropospheric correction with a model-based correction. Our results indicate that both the steric-corrected altimetry and ocean mass reconstruction from GRD-induced sea level change is in agreement with the GRACE observations on both long-term and seasonal time scales and regional scales. We also find that a recent slowdown in GRACE-observed mass change during the GRACE-FO period can be attributed to terrestrial water storage variability driven by a long phase of La Nina and a deceleration in the mass loss of Greenland and Antarctic ice sheets.

Description: Large volcanic eruptions impact climate through the injection of ash and sulfur gas into the atmosphere. While the ash particles fall out rapidly, the gas is converted to sulfate aerosols, which reflect solar radiation in the stratosphere and cause a cooling of the global mean surface temperature. Earlier studies suggested that major volcanic eruptions resulted in positive mass balances and advances of glaciers. Here we perform a multivariate analysis to decompose global glacier mass changes from 1961 to 2005 into components associated with anthropogenic influences, volcanic and solar activity, and El Niño Southern Oscillation (ENSO). We find that the global glacier mass loss was mainly driven by the anthropogenic forcing, interrupted by a few years of intermittent mass gains following large volcanic eruptions. The relative impact of volcanic eruptions is dwindling due to strongly increasing greenhouse gas concentrations since the mid of the 20th century. Furthermore, our study indicates that solar activity and ENSO have limited impacts on climate conditions at glacier locations and that volcanic eruptions alone can hardly explain decadal periods of glacier advances documented since the 16th century.