Joint inversion estimate of regional glacial isostatic adjustment in Antarctica considering a lateral varying Earth structure (ESA STSE Project REGINA)

A major uncertainty in determining the mass balance of the Antarctic ice sheet from measurements of satellite gravimetry, and to a lesser extent satellite altimetry, is the poorly known correction for the ongoing deformation of the solid Earth caused by glacial isostatic adjustment (GIA). Although much progress has been made in consistently modelling the ice-sheet evolution throughout the last glacial cycle, as well as the induced bedrock deformation caused by these load changes, forward models of GIA remain ambiguous due to the lack of observational constraints on the ice sheet's past extent and thickness and mantle rheology beneath the continent. As an alternative to forward modelling GIA, we estimate GIA from multiple space-geodetic observations: GRACE, Envisat/ICESat and GPS. Making use of the different sensitivities of the respective satellite observations to current and past surface mass (ice mass) change and solid Earth processes, we estimate GIA based on viscoelastic response functions to disc load forcing. We calculate and distribute the viscoelastic response functions according to estimates of the variability of lithosphere thickness and mantle viscosity in Antarctica. We compare our GIA estimate with published GIA corrections and evaluate its impact in determining the ice mass balance in Antarctica from GRACE and satellite altimetry. Particular focus is applied to the Amundsen Sea Sector in West Antarctica, where uplift rates of several cm/yr have been measured by GPS. We show that most of this uplift is caused by the rapid viscoelastic response to recent ice-load changes, enabled by the presence of a low-viscosity upper mantle in West Antarctica. This paper presents the second and final contribution summarizing the work carried out within a European Space Agency funded study, REGINA, (www.regina-science.eu)

Altimetry, gravimetry, GPS and viscoelastic modeling data for the joint inversion for glacial isostatic adjustment in Antarctica (ESA STSE Project REGINA)

The poorly known correction for the ongoing deformation of the solid Earth caused by glacial isostatic adjustment (GIA) is a major uncertainty in determining the mass balance of the Antarctic ice sheet from measurements of satellite gravimetry and to a lesser extent satellite altimetry. In the past decade, much progress has been made in consistently modeling ice sheet and solid Earth interactions; however, forward-modeling solutions of GIA in Antarctica remain uncertain due to the sparsity of constraints on the ice sheet evolution, as well as the Earth's rheological properties. An alternative approach towards estimating GIA is the joint inversion of multiple satellite data – namely, satellite gravimetry, satellite altimetry and GPS, which reflect, with different sensitivities, trends in recent glacial changes and GIA. Crucial to the success of this approach is the accuracy of the space-geodetic data sets. Here, we present reprocessed rates of surface-ice elevation change (Envisat/Ice, Cloud,and land Elevation Satellite, ICESat; 2003–2009), gravity field change (Gravity Recovery and Climate Experiment, GRACE; 2003–2009) and bedrock uplift (GPS; 1995–2013). The data analysis is complemented by the forward modeling of viscoelastic response functions to disc load forcing, allowing us to relate GIA-induced surface displacements with gravity changes for different rheological parameters of the solid Earth. The data and modeling results presented here are available in the PANGAEA database (https://doi.org/10.1594/PANGAEA.875745). The data sets are the input streams for the joint inversion estimate of present-day ice-mass change and GIA, focusing on Antarctica. However, the methods, code and data provided in this paper can be used to solve other problems, such as volume balances of the Antarctic ice sheet, or can be applied to other geographical regions in the case of the viscoelastic response functions. This paper presents the first of two contributions summarizing the work carried out within a European Space Agency funded study: Regional glacial isostatic adjustment and CryoSat elevation rate corrections in Antarctica (REGINA)

다중 인공위성 센서 및 기후 모델을 활용한 남극 얼음 질량 변화의 이해

학위논문(박사) -- 서울대학교대학원 : 사범대학 과학교육과(지구과학전공), 2021.8. 서기원.지난 수 십 년 간, 남극의 얼음 질량 변화에 대한 우리의 지식은 인공위성 관측과 지구 물리 모델링 기술의 발전에 의해 비약적으로 향상되어 왔다. 인공위성 관측은 진행중인 남극 얼음 질량 손실과 가속화를 설명할 수 있는 메커니즘들을 지속적으로 제안하고 있으며, 이들을 고려한 모델링은 미래에 진행될 남극 빙하 손실을 정량적으로 산출하고 있다. 현재의 관측과 모델링 모두는 남극의 얼음 배출이 향후에 점차 가속화 될 것이라고 예측하고 있다. 이러한 증가율이 지속된다면, 남극은 가까운 미래에 해수면 상승을 유발시키는 첫번째 기여자가 될 것이다. 남극에서 배출될 빙하의 질량을 정확하게 예측하기 위해서는 진행중인 얼음 질량 손실에 대한 지속적인 관찰과 함께, 그것의 원인 기작을 규명하는 일이 요구된다. 남극의 얼음 질량 변화는 각 빙하마다 비균질하게 발생하고 있으며, 개별 빙하의 동력학은 대기와 해양 순환, 그리고 고체 지구의 변동성 등 다양한 지구 시스템 구성 요소들의 영향을 받고 있다. 각 요소들이 얼음 질량 변화에 미치는 물리적 기작을 보다 정확히 이해하고, 미래 질량 변화 예측의 불확실성을 해소하기 위해서는 이들을 총 망라하는 다학제간 연구가 필요하다. 이러한 흐름의 일환으로, 본 학위 논문에서는 기후 모델들과 원격 탐사 데이터를 활용하여 남극의 얼음 질량 변화를 분석한 세 개의 연구들이 수행되었다. 첫번째 연구는 얼음 질량 변화와 강설량의 관계를 조사한 것으로, 지구 시스템 내의 기권과 빙권 간의 상호작용에 대해 다루고 있다. 조사 결과, 최근 수 십 년 간 발생한 남극의 강설은 얼음 질량 변화의 경년 변동성의 대부분을 설명하고 있었으며, 동 시기 진행된 남극 얼음 질량 손실의 가속화의 약 30%가 강설량 변화의 기여임을 발견하였다. 또한 추가적인 통계분석을 통해, 이러한 강설량 변화가 남반구 극진동 (Southern Annular Mode, SAM) 이라고 불리우는 남반구 고위도의 주기적 기후변화와 밀접한 관련이 있음도 발견하였다. 두 번째 연구에서는 남극 얼음 질량 변화 관측의 해상도를 높이고자 하였다. 이는 빙하 동력학 모델들의 초기 조건을 단일 빙하와 같은 작은 규모에서 효과적으로 제약하기 위한 목적이다. 해상도 증가를 위해, 인공위성 중력계와 고도계 관측 데이터를 융합하는 새로운 선형 역산법을 개발하였다. 역산법의 적용 결과, 남극 대륙 전체의 얼음 질량 변화 (2003-2016) 를 약 27km의 높은 공간 해상도와 함께 한 달의 짧은 샘플링 간격으로 확인할 수 있는 데이터를 산출하였다. 이 연구에서 만든 데이터는 인공위성 중력계나 고도계를 독립적으로 활용하는 것에 비해 더 높은 정확도를 가질 것이라 추측된다. 예를 들어, 새로운 데이터를 활용하여 계산한 남극의 빙하 별 질량 변화는 각 센서를 따로 활용하는 것에 비해, Input-Output 방법이라는 독립적인 관측 결과와 더 높은 유사성을 보이고 있다. 세 번째 연구에서는 남극 빙하 하부의 고체 지구가 유발하는 후빙기 반동 (Glacial Isostatic Adjustment, GIA) 효과를 추정하고자 하였다. 이는 현재의 기술로 관측이 불가능한 GIA 효과가 얼음 질량 관측에 미치는 불확실성를 경감시키기 위한 목적으로 수행되었다. GIA효과를 분리시키기 위해, 앞서 수행한 고해상도 질량 추산 데이터와 다수의 기후모델을 서로 비교하였다. 그 결과, 서남극 로스 빙붕 근처에 위치한 캠 빙류 (Kamb Ice Stream) 하부의 GIA 효과가 효과적으로 분리될 수 있었다. 계산 값을 선행 연구에서 개발된 후빙기 반동 모델들과 비교한 결과, 대부분의 모델들이 캠 빙류의 후빙기 반동을 과대추정하고 있음도 발견하였다. 현존하는 다수의 GIA 모델들에서 캠 빙류 하부의 후빙기 반동 효과가 남극에서 가장 높게 모의되고 있다는 사실을 감안할 때, 이 발견은 모델들의 불확실성을 재고한다는 점에서 남극 얼음 질량 변화에 대한 기존 관측 결과에 시사하는 바가 크다. 세 연구의 결과를 종합한 남극 빙하 배출량 추정과 그에 따른 해수면 상승 예측이 논문의 마지막 장에 제시되어 있다. 이 결과는 대기와 고체 지구의 변동성을 고려함과 동시에, 개별 빙하의 해수면 상승 기여도를 예측하였다는 점에서 이전의 연구들과 차별된다.Over the past few decades, understanding of ice mass changes in Antarctica has been greatly improved by advances in satellite observation and geophysical modeling techniques. Satellite observations have clearly shown evidence of ongoing Antarctic ice mass loss, and numerical models have quantitatively estimated future ice mass loss. Both observation and modeling have found that Antarctic ice mass loss is accelerating and this would continue in the future. Within this century, Antarctica is expected to be the most important contributor to sea-level rise. To accurately predict Antarctic ice mass loss, continuous Antarctic observation is required, and the cause of Antarctic ice mass loss should be understood. Ice mass variations over Antarctic glaciers are determined by many factors, and their magnitudes differ significantly from glaciers to glaciers. Understanding ice mass variations at individual glaciers are important to project future Antarctic ice mass losses and subsequent sea level rise. Because glacier mass balances are affected by different physical mechanisms associated with atmospheric and oceanic circulations and solid earth deformation, multidisciplinary studies have been required for the accurate understanding of the interaction between Antarctic Ice Sheet (AIS) and the entire Earth system. In this dissertation, three studies are carried out using multiple climate models and remote sensing data to understand the current status of glacier mass balance in AIS. The first study examines the role of precipitation in AIS ice mass changes, identifying the interaction between atmosphere and cryosphere. It is found that the precipitation accounts for most of the inter-annual ice mass variability in recent decades and about 30% of the acceleration in contemporary ice mass loss can be explained by precipitation decrease. EOF analysis suggests that such precipitation variability is closely related to periodic climate change in the high altitude of the Southern Hemisphere, named Southern Annular Mode (SAM). After removing effects associated with precipitation decrease, Antarctic ice mass loss associated with glacier dynamics can be obtained. The second study is to develop a new method to improve the spatial resolution of the Antarctic ice mass change by combining two different satellite observations. Antarctic ice mass change in higher resolution can be estimated by a new linear inversion technique using satellite altimetry and gravimetry observations together. The new method provides monthly ice mass changes (2003-2016) for all Antarctic glaciers with a spatial resolution of 27 km. The high-resolution ice mass data agree better with the ice mass change from the Input-Output method than data conventionally obtained either from gravimetry or altimetry satellite. The third study estimates the Glacial Isostatic Adjustment (GIA) effect beneath the Antarctic glaciers. This aims to minimize the GIA error in ice mass observations. By comparing the high-resolution mass estimates with multiple climate models, the GIA effect beneath the Kamb Ice Stream (which is located near the Ross Ice Shelf in West Antarctica) is estimated. The estimated GIA effect is then compared with many GIA models. It is found that most of the GIA models overestimate the GIA effect at the Kamb Ice Stream. Given that a number of models simulate the highest GIA rate beneath the Kamb Ice Stream within Antarctic glaciers, this finding has significant implications to improve the accuracy of Antarctic ice mass change by reducing the GIA uncertainty. Lastly, we aggregate the results of the three studies to project the future mass loss of Antarctic glaciers. This result is distinct from previous studies in that it provides glacial-scale projections of ice mass changes based on ice dynamic effects after removing effects of precipitation and solid earth deformation from glacial-scale ice mass observations.Chapter 1. Introduction 1 Chapter 2. Backgrounds 5 2.1 Satellite gravimetry 5 2.1.1 Overview & Principle 5 2.1.2 Estimation of surface mass densities from GRACE gravity data 6 2.1.3 Spatial filtering 8 2.2 Satellite altimetry 11 2.2.1 Overview & Principle 11 2.2.2 Laser & radar altimetry 12 2.2.3 Data types 13 2.3 Least squares inversion 14 2.3.1 Simple least squares for linear inverse problem 14 2.3.2 Application of least square inversion to GRACE data 16 Chapter 3. Surface mass balance contributions to Antarctic ice mass change investigated by climate models and GRACE gravity data 19 3.1 Introduction 19 3.2 Data & Methods 20 3.2.1 Precipitation models 20 3.2.2 EOF analysis of SMB 21 3.2.3 REOF analysis of SMB 21 3.3 AIS SMB from 1979 to 2017 23 3.4 Observation of AIS SMB 29 3.5 Implications of SMB to present-day ice mass loss in AIS 34 3.6 Conclusion 35 Chapter 4. Estimation of high-resolution Antarctic ice mass balance using satellite gravimetry and altimetry 38 4.1 Introduction 38 4.2 Data 39 4.2.1 GRACE gravity data 39 4.2.2 Satellite altimetry data 40 4.3 Methods 43 4.3.1 Forward Modeling (FM) solution 43 4.3.2 Joint estimation using constrained linear deconvolution 46 4.3.3 Uncertainties 50 4.3.3.1 Uncertainty of GRACE observation 52 4.3.3.2 Uncertainty of FM solution 52 4.3.3.3 Uncertainty of altimetry-based mass loads 54 4.3.3.4 Uncertainty of CLD solution 57 4.4 High resolution Antarctic ice mass loads 59 4.5 AIS glacier mass balance 62 4.6 Conclusion 66 Chapter 5. Estimation of GIA effect beneath the Antarctic Glacier using multiple remote sensing and climate models 68 5.1 Introduction 68 5.2 Data & Method 69 5.2.1 Method 69 5.2.2 Basin boundary 71 5.2.3 SMB models 73 5.2.4 Mass densities from GRACE data 73 5.2.5 Mass densities from satellite altimetry data 74 5.2.6 High-resolution GRACE data and its sensitivity to GIA estimates 75 5.3 Result & Discussion 77 5.3.1 Estimated mass rates 77 5.3.2 GIA mass rate beneath the KIS 80 5.4 Conclusion 81 Chapter 6. Sea-level projections 82 Chapter 7. Conclusion 86 Appendix: Glacial mass variability calculated by satellite gravimetry, altimetry, and their joint estimation 89 References 112 Abstract in Korean 122박

GPS Rates of Vertical Bedrock Motion Suggest Late Holocene Ice-Sheet Readvance in a Critical Sector of East Antarctica

We investigate present-day bedrock vertical motion using new GPS timeseries from the Totten-Denman glacier region of East Antarctica (∼77-120°E) where models of glacial isostatic adjustment (GIA) disagree, glaciers are likely losing mass, and few data constraints on GIA exist. We show that varying surface mass balance loading (SMBL) is a dominant signal, contributing random-walk-like noise to GPS timeseries across Antarctica. In the study region, it induces site velocity biases of up to ∼+1 mm/yr over 2010-2020. After correcting for SMBL displacement and GPS common mode error, subsidence is evident at all sites aside from the Totten Glacier region where uplift is ∼1.5 mm/yr. Uplift near the Totten Glacier is consistent with late Holocene ice retreat while the widespread subsidence further west suggests possible late Holocene readvance of the region’s ice sheet, in broad agreement with limited glacial geological data and highlighting the need for sampling beneath the current ice sheet

Global Sea-Level Budget 1993-Present

Global mean sea level is an integral of changes occurring in the climate system in response to unforced climate variability as well as natural and anthropogenic forcing factors. Its temporal evolution allows changes (e.g.,acceleration) to be detected in one or more components. Study of the sea-level budget provides constraints on missing or poorly known contributions, such as the unsurveyed deep ocean or the still uncertain land water component. In the context of the World Climate Research Programme Grand Challenge entitled Regional Sea Level and Coastal Impacts , an international effort involving the sea-level community worldwide has been recently initiated with the objective of assessing the various datasets used to estimate components of the sea-level budget during the altimetry era (1993 to present). These datasets are based on the combination of a broad range of space-based and in situ observations, model estimates, and algorithms. Evaluating their quality, quantifying uncertainties and identifying sources of discrepancies between component estimates is extremely useful for various applications in climate research. This effort involves several tens of scientists from about 50 research teams/institutions worldwide (www.wcrp-climate.org/grand-challenges/gc-sea-level, last access: 22 August 2018). The results presented in this paper are a synthesis of the first assessment performed during 2017-2018. We present estimates of the altimetry-based global mean sea level (average rate of 3.1 ± 0.3mm yr(-1) and acceleration of 0.1 mm yr(-2) over 1993-present), as well as of the different components of the sea-level budget (http://doi.org/10.17882/54854, last access: 22 August 2018). We further examine closure of the sea-level budget, comparing the observed global mean sea level with the sum of components. Ocean thermal expansion, glaciers, Greenland and Antarctica contribute 42%, 21%, 15% and 8% to the global mean sea level over the 1993-present period. We also study the sea-level budget over 2005-present, using GRACE-based ocean mass estimates instead of the sum of individual mass components. Our results demonstrate that the global mean sea level can be closed to within 0.3 mm yr(-1) (1σ). Substantial uncertainty remains for the land water storage component, as shown when examining individual mass contributions to sea level

Mass balance of the ice sheets and glaciers – progress since AR5 and challenges

Recent research shows increasing decadal ice mass losses from the Greenland and Antarctic Ice Sheets and more generally from glaciers worldwide in the light of continued global warming. Here, in an update of our previous ISMASS paper (Hanna et al., 2013), we review recent observational estimates of ice sheet and glacier mass balance, and their related uncertainties, first briefly considering relevant monitoring methods. Focusing on the response to climate change during 1992-2018, and especially the post-IPCC AR5 period, we discuss recent changes in the relative contributions of ice sheets and glaciers to sea-level change. We assess recent advances in understanding of the relative importance of surface mass balance and ice dynamics in overall ice-sheet mass change. We also consider recent improvements in ice-sheet modelling, highlighting data-model linkages and the use of updated observational datasets in ice-sheet models. Finally, by identifying key deficiencies in the observations and models that hamper current understanding and limit reliability of future ice-sheet projections, we make recommendations to the research community for reducing these knowledge gaps. Our synthesis aims to provide a critical and timely review of the current state of the science in advance of the next Intergovernmental Panel on Climate Change Assessment Report that is due in 2021

GNSS transpolar earth reflectometry exploriNg system (G-TERN): mission concept

The global navigation satellite system (GNSS) Transpolar Earth Reflectometry exploriNg system (G-TERN) was proposed in response to ESA's Earth Explorer 9 revised call by a team of 33 multi-disciplinary scientists. The primary objective of the mission is to quantify at high spatio-temporal resolution crucial characteristics, processes and interactions between sea ice, and other Earth system components in order to advance the understanding and prediction of climate change and its impacts on the environment and society. The objective is articulated through three key questions. 1) In a rapidly changing Arctic regime and under the resilient Antarctic sea ice trend, how will highly dynamic forcings and couplings between the various components of the ocean, atmosphere, and cryosphere modify or influence the processes governing the characteristics of the sea ice cover (ice production, growth, deformation, and melt)? 2) What are the impacts of extreme events and feedback mechanisms on sea ice evolution? 3) What are the effects of the cryosphere behaviors, either rapidly changing or resiliently stable, on the global oceanic and atmospheric circulation and mid-latitude extreme events? To contribute answering these questions, G-TERN will measure key parameters of the sea ice, the oceans, and the atmosphere with frequent and dense coverage over polar areas, becoming a “dynamic mapper”of the ice conditions, the ice production, and the loss in multiple time and space scales, and surrounding environment. Over polar areas, the G-TERN will measure sea ice surface elevation (<;10 cm precision), roughness, and polarimetry aspects at 30-km resolution and 3-days full coverage. G-TERN will implement the interferometric GNSS reflectometry concept, from a single satellite in near-polar orbit with capability for 12 simultaneous observations. Unlike currently orbiting GNSS reflectometry missions, the G-TERN uses the full GNSS available bandwidth to improve its ranging measurements. The lifetime would be 2025-2030 or optimally 2025-2035, covering key stages of the transition toward a nearly ice-free Arctic Ocean in summer. This paper describes the mission objectives, it reviews its measurement techniques, summarizes the suggested implementation, and finally, it estimates the expected performance.Peer ReviewedPostprint (published version

Global sea-level budget 1993–present

none90sìGlobal mean sea level is an integral of changes occurring in the climate system in response to unforced climate variability as well as natural and anthropogenic forcing factors. Its temporal evolution allows changes (e.g., acceleration) to be detected in one or more components. Study of the sea-level budget provides constraints on missing or poorly known contributions, such as the unsurveyed deep ocean or the still uncertain land water component. In the context of the World Climate Research Programme Grand Challenge entitled Regional Sea Level and Coastal Impacts, an international effort involving the sea-level community worldwide has been recently initiated with the objective of assessing the various datasets used to estimate components of the sea-level budget during the altimetry era (1993 to present). These datasets are based on the combination of a broad range of space-based and in situ observations, model estimates, and algorithms. Evaluating their quality, quantifying uncertainties and identifying sources of discrepancies between component estimates is extremely useful for various applications in climate research. This effort involves several tens of scientists from about 50 research teams/institutions worldwide (www.wcrp-climate.org/grand-challenges/gc-sea-level, last access: 22 August 2018). The results presented in this paper are a synthesis of the first assessment performed during 2017–2018. We present estimates of the altimetry-based global mean sea level (average rate of 3.1±0.3mmyr−1 and acceleration of 0.1mmyr−2 over 1993–present), as well as of the different components of the sea-level budget (http://doi.org/10.17882/54854, last access: 22 August 2018). We further examine closure of the sea-level budget, comparing the observed global mean sea level with the sum of components. Ocean thermal expansion, glaciers, Greenland and Antarctica contribute 42%, 21%, 15% and 8% to the global mean sea level over the 1993–present period. We also study the sea-level budget over 2005–present, using GRACE-based ocean mass estimates instead of the sum of individual mass components. Our results demonstrate that the global mean sea level can be closed to within 0.3mmyr−1 (1σ). Substantial uncertainty remains for the land water storage component, as shown when examining individual mass contributions to sea level.NNopenCazenave, Anny; Meyssignac, Benoit; Ablain, Michael; Balmaseda, Magdalena; Bamber, Jonathan; Barletta, Valentina; Beckley, Brian; Benveniste, Jérôme; Berthier, Etienne; Blazquez, Alejandro; Boyer, Tim; Caceres, Denise; Chambers, Don; Champollion, Nicolas; Chao, Ben; Chen, Jianli; Cheng, Lijing; Church, John A.; Chuter, S.; Cogley, J.; Dangendorf, Soenke; Desbruyères, Damien; Döll, Petra; Domingues, Catia; Falk, Ulrike; Famiglietti, James; Fenoglio-Marc, Luciana; Forsberg, Rene; Galassi, Gaia; Gardner, Alex; Groh, Andreas; Hamlington, Benjamin; Hogg, Anna; Horwath, Martin; Humphrey, Vincent; Husson, Laurent; Ishii, Masayoshi; Jaeggi, Adrian; Jevrejeva, Svetlana; Johnson, Gregory; Kolodziejczyk, Nicolas; Kusche, Jürgen; Lambeck, Kurt; Landerer, Felix; Leclercq, Paul; Legresy, Benoit; Leuliette, Eric; Llovel, William; Longuevergne, Laurent; Loomis, Bryant D.; Luthcke, Scott B.; Marcos, Marta; Marzeion, Ben; Merchant, Chris; Merrifield, Mark; Milne, Glenn; Mitchum, Gary; Mohajerani, Yara; Monier, Maeva; Monselesan, Didier; Nerem, Steve; Palanisamy, Hindumathi; Paul, Frank; Perez, Begoña; Piecuch, Christopher G.; Ponte, Rui M.; Purkey, Sarah G.; Reager, John T.; Rietbroek, Roelof; Rignot, Eric; Riva, Riccardo; Roemmich, Dean H.; Sandberg Sørensen, Louise; Sasgen, Ingo; Schrama, E. J. O.; Seneviratne, Sonia I.; Shum, C. K.; Spada, Giorgio; Stammer, Detlef; van de Wal, Roderic; Velicogna, Isabella; von Schuckmann, Karina; Wada, Yoshihide; Wang, Yiguo; Watson, Christopher; Wiese, David; Wijffels, Susan; Westaway, Richard; Woppelmann, Guy; Wouters, BertCazenave, Anny; Meyssignac, Benoit; Ablain, Michael; Balmaseda, Magdalena; Bamber, Jonathan; Barletta, Valentina; Beckley, Brian; Benveniste, Jérôme; Berthier, Etienne; Blazquez, Alejandro; Boyer, Tim; Caceres, Denise; Chambers, Don; Champollion, Nicolas; Chao, Ben; Chen, Jianli; Cheng, Lijing; Church, John A.; Chuter, S.; Cogley, J.; Dangendorf, Soenke; Desbruyères, Damien; Döll, Petra; Domingues, Catia; Falk, Ulrike; Famiglietti, James; Fenoglio-Marc, Luciana; Forsberg, Rene; Galassi, Gaia; Gardner, Alex; Groh, Andreas; Hamlington, Benjamin; Hogg, Anna; Horwath, Martin; Humphrey, Vincent; Husson, Laurent; Ishii, Masayoshi; Jaeggi, Adrian; Jevrejeva, Svetlana; Johnson, Gregory; Kolodziejczyk, Nicolas; Kusche, Jürgen; Lambeck, Kurt; Landerer, Felix; Leclercq, Paul; Legresy, Benoit; Leuliette, Eric; Llovel, William; Longuevergne, Laurent; Loomis, Bryant D.; Luthcke, Scott B.; Marcos, Marta; Marzeion, Ben; Merchant, Chris; Merrifield, Mark; Milne, Glenn; Mitchum, Gary; Mohajerani, Yara; Monier, Maeva; Monselesan, Didier; Nerem, Steve; Palanisamy, Hindumathi; Paul, Frank; Perez, Begoña; Piecuch, Christopher G.; Ponte, Rui M.; Purkey, Sarah G.; Reager, John T.; Rietbroek, Roelof; Rignot, Eric; Riva, Riccardo; Roemmich, Dean H.; Sandberg Sørensen, Louise; Sasgen, Ingo; Schrama, E. J. O.; Seneviratne, Sonia I.; Shum, C. K.; Spada, Giorgio; Stammer, Detlef; van de Wal, Roderic; Velicogna, Isabella; von Schuckmann, Karina; Wada, Yoshihide; Wang, Yiguo; Watson, Christopher; Wiese, David; Wijffels, Susan; Westaway, Richard; Woppelmann, Guy; Wouters, Ber

Global sea level budget 1993-present

Global mean sea level is an integral of changes occurring in the climate system in response to unforced climate variability as well as natural and anthropogenic forcing factors. Its temporal evolution allows detecting changes (e.g., acceleration) in one or more components. Study of the sea level budget provides constraints on missing or poorly known contributions, such as the unsurveyed deep ocean or the still uncertain land water component. In the context of the World Climate Research Programme Grand Challenge entitled “Regional Sea Level and Coastal Impacts”, an international effort involving the sea level community worldwide has been recently initiated with the objective of assessing the various data sets used to estimate components of the sea level budget during the altimetry era (1993 to present). These data sets are based on the combination of a broad range of space-based and in situ observations, model estimates and algorithms. Evaluating their quality, quantifying uncertainties and identifying sources of discrepancies between component estimates is extremely useful for various applications in climate research. This effort involves several tens of scientists from about fifty research teams/institutions worldwide (www.wcrp-climate.org/grand-challenges/gc-sea- level). The results presented in this paper are a synthesis of the first assessment performed during 2017-2018. We present estimates of the altimetry-based global mean sea level (average rate of 3.1 +/- 0.3 mm/yr and acceleration of 0.1 mm/yr2 over 1993-present), as well as of the different components of the sea level budget (http://doi.org/10.17882/54854). We further examine closure of the sea level budget, comparing the observed global mean sea level with the sum of components. Ocean thermal expansion, glaciers, Greenland and Antarctica contribute by 42%, 21%, 15% and 8% to the global mean sea level over the 1993-present. We also study the sea level budget over 2005-present, using GRACE-based ocean mass estimates instead of sum of individual mass components. Results show closure of the sea level budget within 0.3 mm/yr. Substantial uncertainty remains for the land water storage component, as shown in examining individual mass contributions to sea level