Red List of Ecosystems assessment 741
and rose to more than 83mabove the maximum elevation in 2010, and the smoothed freezing level height mean sur- passed the 4,840 m threshold during 1972–1981 (Fig. 3). Using the thresholds of maximum elevation of glacier ice in the two other peaks, we calculated the relative severity of change for this indicator to be 67.2 ± SE 18.5% (Bolívar Peak) and 104.4 ± 28.5% (Humboldt Peak). The large stand- ard error is because of the wide variation in the time series. The best-performing bioclimatic suitability model had
high predictive performance during model training (area under the curve = 0.967 ± SE 0.008,sensitivity = 0.621 ± 0.058 and specificity = 0.981 ± 0.004, with Gradient Boosting Machine model parameters: 200 trees, interaction depth = 5, shrinkage = 0.1 and aminimumof 12 observations per node) and when evaluating model predictions under current cli- matic conditions in the Cordillera de Mérida (area under the curve = 0.990; sensitivity = 0.667 and specificity = 0.996; full model details in Supplementary Material). The best estimate of mean relative severity for this indicator across all combinations of five global circulation models, three pathways, two timeframes and two collapse thresholds is 97%, with a 90% confidence interval of 63–100%. There are three plausible values of difference in equilibrium-line altitude: the historical reconstruction of equilibrium-line altitude between the maximum glacier
extent (pre-1820) and 1972 suggests a value of −300 m, whereas comparison with the historically and recently col- lapsed Mucuñuque and Bolívar Peaks suggests values be-
tween −400 and −500 m (Polissar et al., 2006). Using a value of −550 m as the maximum decline, we calculated
the relative severity of degradation for this indicator and timeframe to be 54–90%, with a median value of 72%. The hybrid model predicted a high probability of col-
lapse in the future. Focusing on the 50-year period 2020– 2070, we found that 79% of the models end in collapse (Fig. 4). Uncertainty in mass estimates (mean absolute devi- ation) does not have a significant effect on the estimated year of collapse. Considering each scenario separately, the proportion of models that predict collapse by 2070 is higher than 50%in all cases, except for the sustainable development scenario (socio-economic pathway 1-2.6). These quantitative results support the assessment of the
risk of collapse using the IUCN Red List of Ecosystems categories and criteria (Table 2).
Discussion
Based on the analyses presented here, the current Red List status of Cordillera de Mérida glacier is Critically Endangered, with plausible evidence that it may already be Collapsed: CR (CR-CO). Almost all of the criteria and sub-criteria assessed indicate theCRstatus, implying similar magnitudes of historical, present and future threats (Table 2). For the Cordillera de Mérida the evidence from recent field visits suggests that its glacier ice will probably disappear before 2048 (sub-criterion A2b). Other lines of evidence suggest similar conclusions, although with more
FIG. 3 Local polynomial regression of freeze level height in the Cordillera de Mérida, Venezuela, for the period 1948–2011, with 95% confidence intervals (based on data from Braun & Bezada, 2013). Horizontal lines represent the last recorded elevation of glacier ice at the different peaks, with years given in parentheses.
FIG. 4 Empirical cumulative distribution function of year of collapse from a global hybrid model of mass balance and glacier dynamics based on future climate predictions from 48 combinations of global circulation models and shared socio-economic pathways (SSPs; thick solid line) and disaggregated by the four different pathway (labelled lines): SSP1-2.6 is a sustainable development scenario, SSP2-4.5 is intermediate, SSP3-7.0 prioritizes national development and SSP5-8.5 is fossil-fuelled development.
Oryx, 2024, 58(6), 735–745 © The Author(s), 2024. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605323001771
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140
