Nature | Vol 584 | 20 August 2020 | 393Article
The causes of sea-level rise since 1900
Thomas Frederikse^1 ✉, Felix Landerer^1 , Lambert Caron^1 , Surendra Adhikari^1 , David Parkes^2 ,
Vincent W. Humphrey^3 , Sönke Dangendorf4,5, Peter Hogarth^6 , Laure Zanna^7 , Lijing Cheng8,9
& Yun-Hao Wu^10The rate of global-mean sea-level rise since 1900 has varied over time, but the
contributing factors are still poorly understood^1. Previous assessments found that
the summed contributions of ice-mass loss, terrestrial water storage and thermal
expansion of the ocean could not be reconciled with observed changes in
global-mean sea level, implying that changes in sea level or some contributions to
those changes were poorly constrained^2 ,^3. Recent improvements to observational
data, our understanding of the main contributing processes to sea-level change and
methods for estimating the individual contributions, mean another attempt
at reconciliation is warranted. Here we present a probabilistic framework to
reconstruct sea level since 1900 using independent observations and their inherent
uncertainties. The sum of the contributions to sea-level change from thermal
expansion of the ocean, ice-mass loss and changes in terrestrial water storage is
consistent with the trends and multidecadal variability in observed sea level on both
global and basin scales, which we reconstruct from tide-gauge records. Ice-mass
loss—predominantly from glaciers—has caused twice as much sea-level rise since
1900 as has thermal expansion. Mass loss from glaciers and the Greenland Ice
Sheet explains the high rates of global sea-level rise during the 1940s, while a sharp
increase in water impoundment by artificial reservoirs is the main cause of the
lower-than-average rates during the 1970s. The acceleration in sea-level rise since the
1970s is caused by the combination of thermal expansion of the ocean and increased
ice-mass loss from Greenland. Our results reconcile the magnitude of observed
global-mean sea-level rise since 1900 with estimates based on the underlying
processes, implying that no additional processes are required to explain the
observed changes in sea level since 1900.Global-mean sea level (GMSL) has increased by approximately
1.5 mm yr−1 (refs.^1 ,^4 ,^5 ) over the twentieth century, modulated by large
multidecadal fluctuations^6. Changes in GMSL are the net result of many
individual geophysical and climatological processes, with some of the
largest contributions coming from ice-mass loss and thermal expansion
of the ocean. The level of agreement between the sum of these individ-
ual contributions and the observed changes in GMSL—often described
as the ‘sea-level budget’—is a key indicator of our understanding of the
drivers of sea-level rise^7. Multiple studies show closure of the sea-level
budget within their stated uncertainties since the 1960s and over the era
of satellite altimetry since 1993^8 –^10. However, rates of GMSL change and
their contributions to the budget over the entire twentieth century, and
especially the first half of the twentieth century, have not yet been fully
explained or attributed. Previous observation-based studies concluded
that the GMSL budget for the whole twentieth century could not be
closed within the estimated uncertainties^2 ,^3. Various explanations for
this non-closure have been proposed, including an overestimation of
the tide-gauge-derived rates of GMSL change^11 and underestimation
of the ice-sheet contribution^12 , but there is no agreement yet on the
cause of this discrepancy^13.
Over the past few years, revised estimates of the main known driving
processes of global sea-level rise that cover the entire twentieth century
have become available^14 –^17 , the spread among different estimates of
twentieth-century glacier mass loss has been reduced^18 , and improved
mapping methods and correction of instrumental bias have resulted
in higher estimates of the contribution from thermal expansion since
the 1960s^19. In parallel, estimates of twentieth-century GMSL change
have converged to lower rates than previously estimated, as a result of
improved reconstruction approaches, spatial-bias correction schemes,
and the inclusion of estimates of local vertical land motion (VLM) at
tide-gauge locations^4 ,^9 ,^20. As a result of these developments, the GMSL
budget needs to be re-estimated, to determine whether the observed
sea-level rise since 1900 can be reconciled with the estimated sum of
contributing processes.https://doi.org/10.1038/s41586-020-2591-3
Received: 21 December 2019
Accepted: 8 June 2020
Published online: 19 August 2020
Check for updates(^1) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA. (^2) Université Catholique de Louvain, Louvain-la-Neuve, Belgium. (^3) Division of Geological and Planetary
Sciences, California Institute of Technology, Pasadena, CA, USA.^4 Center for Coastal Physical Oceanography, Old Dominion University, Norfolk, VA, USA.^5 University of Siegen, Siegen,
Germany.^6 National Oceanography Centre, Liverpool, UK.^7 Courant Institute, New York University, New York, NY, USA.^8 International Center for Climate and Environment Sciences, Institute of
Atmospheric Physics, Chinese Academy of Sciences, Beijing, China.^9 Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China.^10 Research Center for Environmental
Changes, Academia Sinica, Taipei, Taiwan. ✉e-mail: [email protected]