# Low-End Probabilistic Sea-Level Projections

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Data

#### 2.1. Sterodynamic Sea-Level Changes

#### 2.2. Mountain Glaciers

#### 2.3. Greenland

#### 2.4. Antarctica

#### 2.5. Land Water

#### 2.6. Summary of Inputs

## 3. Methods

#### 3.1. Integration: From Sea-Level Contributions to Global and Regional Sea-Level Scenarios

#### 3.2. Probabilistic Distributions for Individual Components to Sea-Level Rise

#### 3.3. Computational Approach and Statistical Dependencies

## 4. Results

#### 4.1. Global Probabilistic Sea-Level Projections

#### 4.2. Regional Sea-Level Projections

## 5. Discussion and Conclusions

- (1)
- (2)
- For Antarctica, we relied on a study that probably underestimated the impact of ocean warming on the Antarctic marine ice-sheet melting, according to its own assessment [7];
- (3)
- For the sterodynamic sea-level changes, we removed AOGCMs giving high thermal expansion values; in the regional AR5 assessment, these outliers increased the mean and uncertainties of the thermal expansion.
- (4)
- We relied on modelling outcomes only, and ignored the procedure consisting of multiplying the standard deviation of model outcomes by 1.64 applied in the AR5; we argue that this procedure artificially extends the lower tail of the distribution of future sea-level rise, whereas AOGCMs have been essentially criticized so far for minimizing future sea-level changes.
- (5)
- We assumed full dependency among the sterodynamic, Mountain Glaciers, and Greenland melting components, which slightly shifts the lower tail of the probability distribution to the right compared to partial dependency schemes;
- (6)
- We did not find physical arguments supporting probabilistic projections below our projections in the published literature.

## Supplementary Materials

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## Appendix A. Sterodynamic Sea-Level Changes (2099, with Respect to 1986–2005)

**Figure A1.**Sterodynamic sea-level changes (in m, for 2099 with respect to 1986–2005) for each climate model used in this study, their mean and standard deviation, for RCP2.6.

**Figure A2.**Sterodynamic sea-level changes (in m, for 2099 with respect to 1986–2005) for each climate model used in this study, their mean and standard deviation, for RCP4.5 and 2099.

**Figure A3.**Mean and standard deviation of sterodynamic sea-level changes (in m, for 2099 with respect to 1986–2005) for RCP2.6, RCP4.5 and RCP8.5 by 2099.

## Appendix B. Regional 5th and 95th Percentiles of the Regional Low-End Sea-Level Projections

**Figure A4.**Low-end regional sea-level projections in 2100 for three RCP scenarios with respect to 1985–2006 (5th and 95th percentiles; unit: m).

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**Figure 1.**Sterodynamic sea-level changes (in m, for 2099 with respect to 1986–2005) for each climate model used in this study, their mean and standard deviation, for RCP8.5 and 2100. See Appendix A for RCP2.6 and RCP4.5.

**Figure 2.**Method to compute global and regional sea-level changes (see Gregory et al., 2019 [42] for the terminology).

**Figure 3.**Bootstrap analysis (using 1000 random replicates) of the Gaussian assumption of contributions to sea-level rise in 2099 for RCP8.5. (

**a**): 21 models used in AR5 (regional results); (

**b**): subset of models used in this study; (

**c**): Greenland [10]; (

**d**): Mountain glaciers [41]. Black dots correspond to the empirical cumulative distribution function and the solid red curve is its Gaussian fit. Dashed red curves indicate maximum and minimum empirical cumulative distributions delivered by the bootstrap procedure. Solid black curves indicate the maximum and minimum Gaussian fits. This figure allows estimating the potential error made with Gaussian assumptions in this study.

**Figure 4.**Global probabilistic sea-level projections obtained in this study (2100, with respect to a 1986–2005 average; unit: m).

**Figure 6.**Regional low-end sea-level scenarios in 2100 for the RCP2.6, 4.5, and 8.5 scenarios (unit: m).

**Table 1.**Comparison of the global mean of sterodynamic sea-level changes to sea-level rise by 2100. The global mean of sterodynamic sea-level changes is theoretically equal to the thermosteric contribution, but some numerical differences can be found (see text). The uncertainties below are those used as input for the global or regional sea-level change computations. Hence, they correspond to one standard deviation of AOGCMs outcomes in this study and in Jackson and Jevrejeva 2016 [45], but the 5–95% range of AOGCMs outcomes in the AR5, in the Integrated Climate Data Center at the Hamburg University dataset and in Kopp et al. (2017) [46].

Reference | RCP2.6 | RCP4.5 | RCP8.5 |
---|---|---|---|

This study | 0.14 ± 0.03 m | 0.20 ± 0.03 m | 0.30 ± 0.03 m |

IPCC AR5 (Global) [1] ^{1} | 0.15 ± 0.05 m | 0.20 ± 0.05 m | 0.32 ± 0.07 m |

Kopp et al. (2014) [19] ^{1} | 0.19 ± 0.06 m | 0.26 ± 0.08 m | 0.37 ± 0.09 m |

Integrated Climate Data Center at the Hamburg University ^{1} | 0.16 ± 0.06 m | 0.21 ± 0.07 m | 0.33 ± 0.10 m |

Jackson et Jevrejeva (2016) [45] | N.A. | 0.21 ± 0.05 m | 0.32 ± 0.07 m |

^{1}In these studies, the standard deviation of model outcomes was multiplied by 1.64.

**Table 2.**Global mean sea-level changes by 2100 relative to 1986–2005 assumed in this study (all Gaussian distributions). For comparison, the AR5 likely range and median contributions are provided for each component in italic and parenthesis, either in the form of “(median ± half the likely range)”, or “(median [likely range])” when the distributions are not centered. All values are rounded at two significant digits beyond the decimal point.

Component | RCP2.6 | RCP4.5 | RCP8.5 |
---|---|---|---|

Thermosteric | 0.14 ± 0.03 m | 0.20 ± 0.03 m | 0.30 ± 0.03 m |

(0.15 ± 0.05 m) | (0.20 ± 0.05 m) | (0.32 ± 0.07 m) | |

Glaciers ^{1} | 0.09 ± 0.02 m | 0.12 ± 0.03 m | 0.17 ± 0.03 m |

(0.11 ± 0.06 m) | (0.13 ± 0.06 m) | (0.18 ± 0.08 m) | |

Greenland ^{1} | 0.04 ± 0.02 m | 0.06 ± 0.02 m | 0.10 ± 0.03 m |

(0.08 ± 0.04 m) | (0.09 [0.05–0.16] m) | (0.15 [0.09–0.28] m) | |

Antarctica ^{1} | 0.02 ± 0.04 m | 0.04 ± 0.04 m | 0.09 ± 0.06 m |

(0.06 ± 0.1 m) | (0.05 ± 0.1 m) | (0.04 [−0.08–0.14] m) | |

Groundwater ^{2} | 0.05 ± 0.08 m | 0.05 ± 0.08 m | 0.05 ± 0.08 m |

0.05 [−0.01–0.11] m | 0.05 [−0.01–0.11] m | 0.05 [−0.01–0.11] m | |

Global isostatic adjustment ^{3} | Based on two different GIA models, as in AR5 [1] |

^{1}Including peripheral glaciers in Greenland and Antarctica for the projections of this paper, and excluding them for the IPCC figures.

^{2}Because we use a Gaussian distribution, our standard deviation is not the same as half the AR5 likely range (see Section 2.5).

^{3}Used for regional projections only.

Correlation Scheme Name | Global Experiments | Regional Experiments |
---|---|---|

“Ind” | All components uncorrelated | All components uncorrelated |

“Dep” | Fully correlated Thermosteric, Mountain Glaciers and Greenland components | Fully correlated Sterodynamic, Mountain Glaciers and Greenland components |

RCP Scenario | 5% | 17% | 50% | 83% | 95% |
---|---|---|---|---|---|

RCP2.6 | 0.17 m | 0.23 m | 0.34 m | 0.45 m | 0.52 m |

RCP4.5 | 0.27 m | 0.35 m | 0.46 m | 0.57 m | 0.63 m |

RCP8.5 | 0.48 m | 0.58 m | 0.70 m | 0.83 m | 0.92 m |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Le Cozannet, G.; Thiéblemont, R.; Rohmer, J.; Idier, D.; Manceau, J.-C.; Quique, R.
Low-End Probabilistic Sea-Level Projections. *Water* **2019**, *11*, 1507.
https://doi.org/10.3390/w11071507

**AMA Style**

Le Cozannet G, Thiéblemont R, Rohmer J, Idier D, Manceau J-C, Quique R.
Low-End Probabilistic Sea-Level Projections. *Water*. 2019; 11(7):1507.
https://doi.org/10.3390/w11071507

**Chicago/Turabian Style**

Le Cozannet, Gonéri, Rémi Thiéblemont, Jeremy Rohmer, Déborah Idier, Jean-Charles Manceau, and Robin Quique.
2019. "Low-End Probabilistic Sea-Level Projections" *Water* 11, no. 7: 1507.
https://doi.org/10.3390/w11071507