On the attribution of industrial-era glacier mass loss to anthropogenic climate change

Roe, Gerard H.; Christian, John E.; Marzeion, Ben

doi:10.5194/tc-2020-265

Cited by 14 publications

(20 citation statements)

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“…L at t = 1880). For this, we draw randomly from the PDF of the glacier's natural variability (Roe andBaker, 2014, 2016). For each 140-year period, we calculate the mass bal-ance (e.g.…”

Section: Estimates Of Natural Variability From Instrumental Recordsmentioning

confidence: 99%

On the attribution of industrial-era glacier mass loss to anthropogenic climate change

2021

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Abstract. Around the world, small ice caps and glaciers have been losing mass and retreating since the start of the industrial era. Estimates are that this has contributed approximately 30 % of the observed sea-level rise over the same period. It is important to understand the relative importance of natural and anthropogenic components of this mass loss. One recent study concluded that the best estimate of the magnitude of the anthropogenic mass loss over the industrial era was only 25 % of the total, implying a predominantly natural cause. Here we show that the anthropogenic fraction of the total mass loss of a given glacier depends only on the magnitudes and rates of the natural and anthropogenic components of climate change and on the glacier's response time. We consider climate change over the past millennium using synthetic scenarios, palaeoclimate reconstructions, numerical climate simulations, and instrumental observations. We use these climate histories to drive a glacier model that can represent a wide range of glacier response times, and we evaluate the magnitude of the anthropogenic mass loss relative to the observed mass loss. The slow cooling over the preceding millennium followed by the rapid anthropogenic warming of the industrial era means that, over the full range of response times for small ice caps and glaciers, the central estimate of the magnitude of the anthropogenic mass loss is essentially 100 % of the observed mass loss. The anthropogenic magnitude may exceed 100 % in the event that, without anthropogenic climate forcing, glaciers would otherwise have been gaining mass. Our results bring assessments of the attribution of glacier mass loss into alignment with assessments of others aspects of climate change, such as global-mean temperature. Furthermore, these results reinforce the scientific and public understanding of centennial-scale glacier retreat as an unambiguous consequence of human activity.

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“…L at t = 1880). For this, we draw randomly from the PDF of the glacier's natural variability (Roe andBaker, 2014, 2016). For each 140-year period, we calculate the mass bal-ance (e.g.…”

Section: Estimates Of Natural Variability From Instrumental Recordsmentioning

confidence: 99%

On the attribution of industrial-era glacier mass loss to anthropogenic climate change

2021

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“…Secondly, for the industrial era (since about 1880 or so), the central estimate of the warming from anthropogenic forcing is 100 % of the observed warming, both globally and regionally (Haustein et al, 2019). This implies that both the observed industrial-era mass loss (Roe et al, 2020) and retreat (Roe et al, 2017) of Alpine glaciers is overwhelmingly anthropogenic in origin.…”

Section: Introductionmentioning

confidence: 99%

Understanding drivers of glacier-length variability over the last millennium

et al. 2021

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Abstract. Changes in glacier length reflect the integrated response to local fluctuations in temperature and precipitation resulting from both external forcing (e.g., volcanic eruptions or anthropogenic CO2) and internal climate variability. In order to interpret the climate history reflected in the glacier moraine record, the influence of both sources of climate variability must therefore be considered. Here we study the last millennium of glacier-length variability across the globe using a simple dynamic glacier model, which we force with temperature and precipitation time series from a 13-member ensemble of simulations from a global climate model. The ensemble allows us to quantify the contributions to glacier-length variability from external forcing (given by the ensemble mean) and internal variability (given by the ensemble spread). Within this framework, we find that internal variability is the predominant source of length fluctuations for glaciers with a shorter response time (less than a few decades). However, for glaciers with longer response timescales (more than a few decades) external forcing has a greater influence than internal variability. We further find that external forcing also dominates when the response of glaciers from widely separated regions is averaged. Single-forcing simulations indicate that, for this climate model, most of the forced response over the last millennium, pre-anthropogenic warming, has been driven by global-scale temperature change associated with volcanic aerosols.

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“…The future evolution of glaciers' mass balances is usually estimated using numerical models (Hock et al, 2019;Marzeion et al, 2020). This is the case for the more distant past as well (e.g., Goosse et al, 2018;Parkes and Goosse, 2020), since glaciers are mostly situated in remote locations and thus lacking comprehensive in-situ measurement densities, at least before 1950 (WGMS, 2020).…”

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confidence: 99%

“…It is therefore important to assess and improve glacier mass balance models used to reconstruct or project glacier evolution. An ensemble-based, long-term reconstruction can add to our understanding of the uncertainties in glacier modeling, which might in turn enhance our ability to make more robust projections of glacier mass loss (Hock et al, 2019;Marzeion et al, 2020). The modeling approaches to establishing global estimates for the glaciers' mass balances mostly make use of temperature index melt models to represent the energy available for melting precipitation and ice (e.g., Huss and Hock, 2015;Radić and Hock, 2011;Hirabayashi et al, 2013).…”

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20th century global glacier mass change: an ensemble-based model reconstruction

Malles¹,

Marzeion²

2020

Preprint

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Abstract. Negative glacier mass balances in most of Earth's glacierized regions contribute roughly one quarter to currently observed rates of sea-level rise, and have likely contributed an even larger fraction during the 20th century. The distant past and future of glaciers' mass balances, and hence their contribution to sea-level rise, can only be calculated using numerical models. Since independent of complexity, models always rely on some form of parameterizations and a choice of boundary conditions, a need for optimization arises. In this work, a model for computing monthly mass balances of glaciers on the global scale was forced with nine different data sets of near-surface air temperature and precipitation anomalies, as well as with their mean and median, leading to a total of eleven different forcing data sets. Five global parameters of the model’s mass balance equations were varied systematically, within physically plausible ranges, for each forcing data set. We then identified optimal parameter combinations by cross-validating the model results against in-situ mass balance observations, using three criteria: model bias, temporal correlation, and the ratio between the observed and modeled temporal standard deviation of specific mass balances. The goal is to better constrain the glaciers' 20th century sea-level budget contribution and its uncertainty. We find that the disagreement between the different ensemble members is often larger than the uncertainties obtained via cross-validation, particularly in times and places where few or no validation data are available, such as the first half of the 20th century. We show that the reason for this is that the availability of mass balance observations often coincides with less uncertainty in the forcing data, such that the cross-validation procedure does not capture the true out-of-sample uncertainty of the glacier model. Therefore, ensemble spread is introduced as an additional estimate of reconstruction uncertainty, increasing the total uncertainty compared to the model uncertainty obtained in the cross validation. Our ensemble mean estimate indicates a sea-level contribution by global glaciers (excluding Antarctic periphery) for 1901–2018 of 76.2 ± 5.9 mm sea-level equivalent (SLE), or 0.65 ± 0.05 mm SLE yr−1.

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On the attribution of industrial-era glacier mass loss to anthropogenic climate change

Cited by 14 publications

References 20 publications

On the attribution of industrial-era glacier mass loss to anthropogenic climate change

On the attribution of industrial-era glacier mass loss to anthropogenic climate change

Understanding drivers of glacier-length variability over the last millennium

20th century global glacier mass change: an ensemble-based model reconstruction

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