Revisiting the contemporary sea-level budget on global and regional scales

Abstract

Dividing the sea-level budget into contributions from ice sheets and glaciers, the water cycle, steric expansion, and crustal movement is challenging, especially on regional scales. Here, Gravity Recovery And Climate Experiment (GRACE) gravity observations and sea-level anomalies from altimetry are used in a joint inversion, ensuring a consistent decomposition of the global and regional sea-level rise budget. Over the years 2002-2014, we find a global mean steric trend of 1.38 ± 0.16 mm/y, compared with a total trend of 2.74 ± 0.58 mm/y. This is significantly larger than steric trends derived from in situ temperature/salinity profiles and models which range from 0.66 ± 0.2 to 0.94 ± 0.1 mm/y. Mass contributions from ice sheets and glaciers (1.37 ± 0.09 mm/y, accelerating with 0.03 ± 0.02 mm/y 2 ) are offset by a negative hydrological component (−0.29 ± 0.26 mm/y). The combined mass rate (1.08 ± 0.3 mm/y) is smaller than previous GRACE estimates (up to 2 mm/y), but it is consistent with the sum of individual contributions (ice sheets, glaciers, and hydrology) found in literature. The altimetric sea-level budget is closed by coestimating a remaining component of 0.22 ± 0.26 mm/y. Well above average sea-level rise is found regionally near the Philippines (14.7 ± 4.39 mm/y) and Indonesia (8.3 ± 4.7 mm/y) which is dominated by steric components (11.2 ± 3.58 mm/y and 6.4 ± 3.18 mm/y, respectively). In contrast, in the central and Eastern part of the Pacific, negative steric trends (down to −2.8 ± 1.53 mm/y) are detected. Significant regional components are found, up to 5.3 ± 2.6 mm/y in the northwest Atlantic, which are likely due to ocean bottom pressure variations.lobal sea-level rise has been identified as one of the major threats associated with global climate change (1, 2). However, from the perspective of assessment-and decision-making, regional estimates of sea-level rise are even more important to formulate meaningful adaptation plans on a national or international level. Besides the magnitude of the total sea-level rise itself, identifying dominant drivers, and their corresponding uncertainties, may also prove beneficial for projection studies.Historical records from tide gauges indicate a sea-level rate of about 1.7 mm/y over the period 1900-2009, where it must be noted that tide gauges indicate an acceleration (0.009-0.017 mm/y 2 ) over the last century (3-5). Besides the steric expansion of sea water due to temperature changes, the ongoing melting and ablation of ice sheets in Greenland and Antarctica and other land glaciers cause the sea level to rise. Hydrological mass variability on land and reservoir construction have been found to cause a negative trend (6-9). Furthermore, meltwater, precipitation, or evaporation result in regional salinity changes, leaving steric signatures in sea level once the barotropic component has been compensated (10). For an observer at the coast, crustal movement, caused by glacial isostatic adjustment (GIA), tectonics, or local subsidence may also significantly affect the r...

Tropical limestone forest resilience and late Pleistocene foraging during MIS-2 in the Tràng An massif, Vietnam

“…The effects of modern climate change on tropical environments had been seen as secondary to that predicted from deforestation and extractive industry (Sala et al 2000); however, the projected climate-driven impact on environments and communities in Southeast Asia has grown significantly in the last decade. Coastal and low-lying island habitats and their associated populations are now known to face an acute threat from climate-driven inundation and environmental transformation (Nicholls & Cazenave 2010;Rietbroek et al 2016). While the corpus of literature on the impact to coastal habitats globally gathers apace (e.g.…”

Observation-Based Estimates of Global Glacier Mass Change and Its Contribution to Sea-Level Change

“…The most recent global estimates of glacier mass changes include Jacob et al (2012) with 0.41 ± 0.08 mm SLE year -1 (2003-2010 time period) and Schrama et al (2014) with 0.45 ± 0.03 mm SLE year -1 (2003-2013) using the mascon-based approach, Chen et al (2013) with 0.54 ± 0.10 mm SLE year -1 (2005)(2006)(2007)(2008)(2009)(2010)(2011) and Yi et al (2015) with 0.58 ± 0.04 mm SLE year -1 (2005-2014) using the forward modeling-based method, and the four following studies which combined GRACE-based estimates with other datasets (e.g., altimetry, literature assessment, sea-level budget approach): Gardner et al (2013) with 0.60 ± 0.08 mm SLE year -1 (2003-2009), Dieng et al (2015) with 0.58 ± 0.1 mm SLE year -1 (2003-2013), Reager et al (2016), an update of Gardner et al (2013), with 0.53 ± 0.09 mm SLE year -1 (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014) and Rietbroek et al (2016) with 0.38 ± 0.07 mm SLE year -1 (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014). See Fig.…”

“…On the other hand, particularly the largest glaciers with flat and thick tongues often only have weakly inclined or even retrograde beds. This leads to down-wasting rather than dynamically active retreat to higher elevations and may Jacob et al (2012), G13 is Gardner et al (2013), C13 is Chen et al (2013), S14 is Schrama et al (2014), D15 is Dieng et al (2015), Y15 is Yi et al (2015), Re16 is Reager et al (2016) and Ri16 is Rietbroek et al (2016) prevent a recovery of the glacier tongue once the surface lowering has started. Because of the delayed response of glaciers to climate forcing, these feedbacks are not simple to capture in glacier models in reconstructive mode: to estimate the past glacier geometry, the past mass balance has to be known, which itself is a function of the past geometry.…”

A Blue Urban Agenda: Adapting to Climate Change in the Coastal Cities of Caribbean and Pacific Small Island Developing States

“…The annual projected change in sea level between two time periods nearly one hundred year apart (1986-2005 and 2081-2100) is 0.5 to 0.6m in the Caribbean, the Northern Tropical Pacific, and the Southern Pacific (Nurse et al, 2014). More recent estimates show a trend in the relative SLR for the coastal zones in the Caribbean East as 3.5 (±3.22) millimetres per year and the Caribbean Sea 2.0 (±3.14) millimetres (Rietbroek, Brunnabend, Kusche, et al, 2016).In contrast to other geographic areas, small islands are at greater risk from SLR because most of their population and infrastructure are concentrated in the coastal zone. Conservative estimates suggest that nearly 11 percent of people in SIDS live (with striking variations between the states) in zones where the elevation is below 5 metres (UN-Habitat, 2015).…”