Different sea level reconstructions show a spread in sea level rise over the last six decades and it is not yet certain whether the sum of contributors explains the reconstructed rise. Possible causes for this spread are, among others, vertical land motion at tide-gauge locations and the sparse sampling of the spatially variable ocean. To assess these open questions, reconstructed sea level and the role of the contributors are investigated on a local, basin, and global scale. High-latitude seas are excluded. Tide-gauge records are combined with observations of vertical land motion, independent estimates of ice-mass loss, terrestrial water storage, and barotropic atmospheric forcing in a self-consistent framework to reconstruct sea level changes on basin and global scales, which are compared to the estimated sum of contributing processes. For the first time, it is shown that for most basins the reconstructed sea level trend and acceleration can be explained by the sum of contributors, as well as a large part of the decadal variability. The sparsely sampled South Atlantic Ocean forms an exception. The global-mean sea level reconstruction shows a trend of 1.5 ± 0.2 mm yr-1 over 1958-2014 (1σ), compared to 1.3 ± 0.1 mm yr-1 for the sum of contributors. Over the same period, the reconstruction shows a positive acceleration of 0.07 ± 0.02 mm yr-2, which is also in agreement with the sum of contributors, which shows an acceleration of 0.07 ± 0.01 mm yr-2. Since 1993, both reconstructed sea level and the sum of contributors show good agreement with altimetry estimates.@en

The rate at which global mean sea level (GMSL) rose during the 20th century is uncertain, with little consensus between various reconstructions that indicate rates of rise ranging from 1.3 to 2 mm•y-1. Here we present a 20th-century GMSL reconstruction computed using an area-weighting technique for averaging tide gauge records that both incorporates up-to-date observations of vertical land motion (VLM) and corrections for local geoid changes resulting from ice melting and terrestrial freshwater storage and allows for the identification of possible differences compared with earlier attempts. Our reconstructed GMSL trend of 1.1 ± 0.3 mm•y-1 (1s) before 1990 falls below previous estimates, whereas our estimate of 3.1 ± 1.4 mm•y-1 from 1993 to 2012 is consistent with independent estimates from satellite altimetry, leading to overall acceleration larger than previously suggested. This feature is geographically dominated by the Indian Ocean-Southern Pacific region, marking a transition from lower-than-average rates before 1990 toward unprecedented high rates in recent decades. We demonstrate that VLM corrections, area weighting, and our use of a common reference datum for tide gauges may explain the lower rates compared with earlier GMSL estimates in approximately equal proportion. The trends and multidecadal variability of our GMSL curve also compare well to the sum of individual contributions obtained from historical outputs of the Coupled Model Intercomparison Project Phase 5. This, in turn, increases our confidence in process-based projections presented in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.@en

The rate at which global mean sea level (GMSL) rose during the 20th century is uncertain, with little consensus between various reconstructions that indicate rates of rise ranging from 1.3 to 2 mm•y-1. Here we present a 20th-century GMSL reconstruction computed using an area-weighting technique for averaging tide gauge records that both incorporates up-to-date observations of vertical land motion (VLM) and corrections for local geoid changes resulting from ice melting and terrestrial freshwater storage and allows for the identification of possible differences compared with earlier attempts. Our reconstructed GMSL trend of 1.1 ± 0.3 mm•y-1 (1s) before 1990 falls below previous estimates, whereas our estimate of 3.1 ± 1.4 mm•y-1 from 1993 to 2012 is consistent with independent estimates from satellite altimetry, leading to overall acceleration larger than previously suggested. This feature is geographically dominated by the Indian Ocean-Southern Pacific region, marking a transition from lower-than-average rates before 1990 toward unprecedented high rates in recent decades. We demonstrate that VLM corrections, area weighting, and our use of a common reference datum for tide gauges may explain the lower rates compared with earlier GMSL estimates in approximately equal proportion. The trends and multidecadal variability of our GMSL curve also compare well to the sum of individual contributions obtained from historical outputs of the Coupled Model Intercomparison Project Phase 5. This, in turn, increases our confidence in process-based projections presented in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.@en

In this paper we discuss our efforts to perform precision orbit determination (POD) of CryoSat-2 which depends on Doppler and satellite laser ranging tracking data. A dAll processes that affect sea level show distinct regional patterns, and therefore, sea-level changes show considerable spatial variability. This spatial variability forms a challenge when reconstructing global and regional sea-level changes from tide gauges, which are only available at a limited number of locations and are mostly located along coasts in the northern hemisphere. We can improve estimates of global and regional sea-level changes from tide-gauge records by explicitly taking the expected spatial variability into account. From estimates of global ice mass loss and land water storage changes, spatial sea-level fingerprints can be computed, which identify whether sea-level changes at specific tide-gauge locations are expected to be representative for global-mean or basin-mean sea-level changes. Furthermore, developments in altimetry and GPS now allow for reliable estimates of local vertical land motion (VLM) at an increased number of tide gauges. We reconstruct global and regional sea-level changes since 1958 by combining the expected sea-level fingerprints with observations from tide gauges and GPS stations. The spatial sea-level fingerprints associated with glacial isostatic adjustment (GIA) and present-day ice mass loss and land water storage are used to detect and correct possible biases due to the uneven spatial sampling of the tide-gauge observations. The fingerprints that emerge from GIA and present-day mass redistribution have an earth-deformation component, which is also observed as VLM. Hence, care must be taken when combining spatial sea-level fingerprints with VLM observations to avoid double-counting of solid-earth deformation. By separating observed land motion into known and unknown sources, this double-counting is avoided. For most ocean basins, the reconstructed sea-level changes can be explained by the combined effects of GIA, present-day mass redistribution, and ocean density effects. A substantial part of the observed decadal variability can be explained by ocean density variations, while trends and accelerations are mostly driven by ice and land water storage changes. The only exception is the South Atlantic Ocean. In this basin, reconstructed sea level cannot be reconciled with the underlying processes, which is probably related to the sparse tide-gauge coverage in this region. When the regional sea-level estimates are merged into a global-mean estimate, we find a GMSL trend of 1.5 0.2 mm/yr, and an acceleration of 0.07 0.02 mm/yr2. Both the global-mean trend and the acceleration can be explained by the sum of contributing processes, and hence, the global sea-level budget since 1958 can be considered closed without requiring a contribution of deep-ocean thermal expansion or pre-1990 Antarctic mass loss, although substantial uncertainty remains due to the sparsely-observed South Atlantic Ocean. ynamic orbit model is set-up and the residuals between the model and the tracking data is evaluated. The average r.m.s. of the 10 second averaged Doppler tracking pass residuals is approximately 0.39 mm/s; and the average of the laser tracking pass residuals becomes 1.42 cm. We discuss three improvements that have brought the orbit accuracy to this level, it concerns the way we implement temporal gravity accelerations observed by GRACE; the implementation of ITRF2014 coordinates and velocities for the DORIS beacons and the SLR tracking sites. We also discuss an adjustment of the SLR retroreflector position within the satellite reference frame. An unexpected result is that we find a systematic difference between the median of the 10s Doppler tracking residuals which displays a statistically significant pattern in the South Atlantic Anomaly area where the median of the velocity residuals varies in the range of -0.15 to +0.15 mm/s@en