A global synthesis of biodiversity responses to glacier retreat. The temperature-index model includes up to three different DDFs, for ice, firn and snow, resulting in three parameters. When comparing our deep learning simulations with those from the Lasso, we found average cumulative MB differences of up to 17% by the end of the century (Fig. Ice thickness accuracy varied significantly, with an overall correct representation of the ice distribution but with local biases reaching up to 100%. Bolibar, J. et al. This means that these differences linked to MB nonlinearities observed in this experiment could be even greater for such ice caps. In order to avoid overfitting, MB models were thoroughly cross-validated using all data for the 19672015 period in order to ensure a correct out-of-sample performance. ALPGM uses a feed-forward fully connected multilayer perceptron, with an architecture (40-20-10-5-1) with Leaky-ReLu44 activation functions and a single linear function at the output. Since the neural network used here virtually behaves like a black box, an alternative way is needed to understand the models behaviour. As the Earth heats up due to climate change, glaciers are melting. Sci. Average ice velocities on the Nisqually Glacier were previously measured at approximately 200 mm/day (8 in) (Hodge 1974). & Zumbhl, H. J. The original ice thickness estimates of the methods used by both models are different10,32, and for ALPGM we performed some additional modifications to the two largest glaciers in the French Alps (see Glacier geometry evolution for details). A glacier flows naturally like a river, only much more slowly. The maximum downvalley position of the glacier is marked by either a This will reduce the importance of shortwave radiation for future ablation rates, and it is expected to result in a reduction in values of degree-day factors (DDFs) and therefore a significant change in melt sensitivity to air temperature variations36. a deep artificial neural network) or the Lasso (regularized multilinear regression)30. MathSciNet J. Glaciol. These conclusions drawn from these synthetic experiments could have large implications given the important sea-level contribution from ice cap-like ice bodies8. a1) over the French Alps. Braithwaite, R. J. With a secondary role, glacier model uncertainty decreases over time, but it represents the greatest source of uncertainty until the middle of the century8. Soc. This means that these flatter ice bodies, under a warming climate, will be subject to higher temperatures than their steeper counterparts. Ice-surface altitude changes of as much as 25 meters occurred between 1944 and 1955. The maximum advance of Nisqually Glacier in the last thousand years was located, and retreat from this point is believed to have started about 1840. Gardent, M., Rabatel, A., Dedieu, J.-P. & Deline, P. Multitemporal glacier inventory of the French Alps from the late 1960s to the late 2000s. Google Scholar. All authors provided inputs to the paper and helped to write it. The cumulative positive degree days (CPDD), snowfall and rainfall dl, are at the glaciers annually evolving centroids. Ten . Clim. 1960). Internet Explorer). snowfall, avalanches and refreezing) and the mass lost via different processes of ablation (e.g. Through these surveys "bulges" have been tracked as they travel down the glacier (c). Both models agree around the average values seen during training (i.e. An accurate prediction of future glacier evolution will be crucial to successfully adapt socioeconomic models and preserve biodiversity. Res. Multiple copies of this dataset were created, and for each individual copy a single predictor (i.e. Earth Syst. contributed to the extraction of nonlinear mass balance responses and to the statistical analysis. In fact, in many cases the surface lowering into warmer air causes this impact on the MB to be negative, further enhancing extreme negative mass balance rates. Moreover these three aspects of glacier behavior are inextricably interwoven: a high sensitivity to climate change goes hand-in-hand with a large natural variability. Under warmer conditions (RCP 8.5), the differences between the linear and nonlinear MB model become smaller, as the topographical feedback from glacier retreat compensates for an important fraction of the losses induced by the late century warmer climate (Fig. Despite the existence of slightly different trends during the first half of the century, both the Lasso and the temperature-index model react similarly under RCP 4.5 and 8.5 during the second half of the century, compared to the deep learning model. In order to investigate the effects of MB nonlinearities on flatter glaciers, we conducted a synthetic experiment using the French Alps dataset. Through synthetic experiments, we showed that the associated uncertainties are likely to be even more pronounced for ice caps, which host the largest reserves of ice outside the two main ice sheets32. The ice thickness data for two of the largest glaciers in the French Alps were modified in order to improve data quality. The climatic forcing comes from high-resolution climate ensemble projections from 29 combinations of global climate models (GCMs) and regional climate models (RCMs) adjusted for mountain regions for three Representative Concentration Pathway (RCP) scenarios: 2.6, 4.5, and 8.525. J. Appl. H.Z. Uncertainties of existing projections of future glacier evolution are particularly large for the second half of the 21st century due to a large uncertainty on future climatic conditions. Planet. Predicting future glacier evolution is of paramount importance in order to correctly anticipate and mitigate the resulting environmental and social impacts. provided glacier mass balance data and performed the glaciological analyses. P. Kennard, J. This translates into more frequent extreme negative MB rates, and therefore greater differences due to nonlinearities for the vast majority of future climate scenarios (Fig. We reduced these differences by running simulations with GloGEMflow using exactly the same 29 climate members used by ALPGM in this study (TableS1). Geophys. Sign up for the Nature Briefing newsletter what matters in science, free to your inbox daily. Glacier topography is a crucial driver of future glacier projections and is expected to play an important role in determining the magnitude that nonlinearities will have on the mass balance signal: ice caps and large flatter glaciers are expected to be more influenced by these nonlinear sensitivities than steep mountain glaciers in a warming climate. A He uniform initialization45 was used for the network parameters. Our results suggest that, except for the lowest emissions climate scenarios and for large glaciers with long response times, MB models with linear relationships for PDDs and precipitation are suitable for mountain glaciers with a marked topographical feedback. GlacierMIP A model intercomparison of global-scale glacier mass-balance models and projections. Z. et al. Ioffe, S. & Szegedy, C. Batch Normalization: Accelerating Deep Network Training by Reducing Internal Covariate Shift (2015). Due to the statistical nature of the Lasso model, the response to snowfall anomalies is also highly influenced by variations in PDDs (Fig. Smiatek, G., Kunstmann, H. & Senatore, A. EURO-CORDEX regional climate model analysis for the Greater Alpine Region: performance and expected future change: climate change in the gar area. The new research suggests that the world's glaciers are disappearing more quickly than scientists previously estimated, and they . Graphics inspired by Hock and Huss40. The position of the front of the wave will be defined as the transverse line across the glacier where the flow of . Advances occurred from 1963-68 and from 1974-79. creates a Nisqually Glacier response similar to those seen from its historical waves, suggesting that there are other factors contributing to kinematic wave formation, and 4) the Nisqually . 3). Alternatively, the comparisons against an independent large-scale glacier evolution model were less straightforward to achieve. An analysis of the climate signal at the glaciers mean altitude throughout the century reveals that air temperature, particularly in summer, is expected to be the main driver of glacier mass change in the region (Fig. J. Glaciol. Cross-validation strategies for data with temporal, spatial, hierarchical, or phylogenetic structure. Model Dev. Strong Alpine glacier melt in the 1940s due to enhanced solar radiation. Secure .gov websites use HTTPS A lock ( ) or https:// means you've safely connected to the .gov website. 1d, g). On the other hand, for flatter glaciers large differences between deep learning and Lasso are obtained for almost all climate scenarios (Fig. The glacier ice volume in the French Alps at the beginning of the 21st century is unevenly distributed, with the Mont-Blanc massif accounting for about 60% of the total ice volume in the year 2015 (7.06 out of 11.64km3, Fig. regularized multilinear regression. This is particularly important for the ablation season and for ice DDFs, which need to accommodate the progressively decreasing role that shortwave radiation will play in the future glacier surface energy budget under warmer conditions. Evol. Earth Planet. Both DEMs were resampled and aligned at a common spatial resolution of 25m. For each glacier, an individual parameterized function was computed representing the differences in glacier surface elevation with respect to the glaciers altitude within the 19792011 period. The rest of the story appears to lie primarily in the unique dynamic response of the region's glaciers to climate change. Regarding air temperature forcings, the linear Lasso MB model was found to be slightly under-sensitive to extreme positive cumulative PDD (CPDD) and over-sensitive to extreme negative CPDDs. The vertical blue and red lines indicate the distribution of extreme (top 5%) values for all 21st century projected climate scenarios, with the mean value in the center and 1 indicated by dashed lines. In our model, we specifically computed this parameterized function for each individual glacier larger than 0.5km2, representing 80% of the total glacierized area in 2015, using two DEMs covering the whole French Alps: a photogrammetric one in 1979 and a SPOT-5 one in 2011. S5b). Partitioning the uncertainty of ensemble projections of global glacier mass change. Sci. These are among the cascading effects linked to glacier loss which impact ecosystems and . GloGEMflow relies on EURO-CORDEX ensembles26, whereas ALPGM uses ADAMONT25, an adjusted version of EURO-CORDEX specifically designed for mountain regions. Reanalysis of 47 Years of Climate in the French Alps (19582005): Climatology and Trends for Snow Cover. Tibshirani, R. Regression Shrinkage and Selection via the Lasso. A comparison between the two MB models shows that a nonlinear response to climate forcings is captured by the deep learning MB model, allowing a better representation of glacier mass changes, including significantly reduced biases for extreme values (see Methods). Glaciers are large-scale, highly sensitive climate instruments which, ideally, should be picked up and weighed once a year. In the past, shortwave radiation represented a more important fraction in the glacier surface energy budget than the energy fluxes directly related to air temperature (e.g. 12, 1959 (2020). S6). Consequently, a simple MB model with a single DDF (e.g. MB rates only begin to approach equilibrium towards the end of the century under RCP 2.6, for which glaciers could potentially stabilize with the climate in the first decades of the 22nd century depending on their response time (Fig. The same was done with winter snowfall anomalies, ranging between 1500mm and +1500mm in steps of 100mm, and summer snowfall anomalies, ranging between 1000mm and +1000mm in steps of 100mm. Res. Tests were performed distributing the CPDD anomalies equally among all months of the year with very similar results. Therefore, linear MB models present more limitations for projections of ice caps, showing a tendency to negative MB biases. Sci. This translates into a more linear response to air temperature changes compared to the ablation season (Fig. CoRR abs/1505.00853 (2015). Alluvial landscape response to climate change in glacial rivers and the implications to transportation infrastructure.
Pressreader Pawtucket Times,
Stevie Nicks Tour 2022 Merchandise,
Articles N