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OCEANOBS19 (Article for Frontiers in Marine Science)
Observational requirements for long-term monitoring
of the global mean sea level and its components
over the altimetry era
Anny Cazenave1,2, Ben Hamlington3, Martin Horwath4,
Valentina Barletta5, Jérôme Benveniste6, Don Chambers7,
Petra Döll8, Anna Hogg9, Jean François Legeais10, Mark Merrifield11,
Benoit Meyssignac1, Garry Mitchum7, Steve Nerem12, Roland Pail13,
H. Palanisamy1, Frank Paul14, Karina von Schuckmann15, P. Thompson16
A leading indicator of global climate change
integrated response to changes in ocean heat
content, land ice & land water storage to external
forcings (including anthropogenic forcing) and to internal climate variability
Global Mean Sea Level Rise
GCOS, 2018; WMO, 2018
The 7 global indicators of present-day climate change
defined by GCOS (Global Climate Observing System)
and WMO (World Meteorological Organization)
Key questions related to sea level research (e.g., « Thriving on our changing Planet;
A decadal strategy for Earth Observation from Space,
The National Academies, 2018)
How much will sea level rise, globally and regionally, over
the next decade and beyond, in response to ice sheet mass
loss and ocean warming?
How will sea level change along the world coastlines?
Global Mean Sea Level (GMSL) over the altimetry era
January 1993 end of May 2019
Mean rate of rise: 3.1 +/- 0.3 mm/yr
Acceleration : 0.1 mm/yr2
Source: LEGOS
8 cm
6
Regional rates of sea level change (1993-2018) (mm/yr)
Observed Global Mean Sea Level =
Ocean Thermal Expansion + Ocean Mass
Global Mean Sea Level Budget
Ocean
Mass
Budget
ΔMocean = - ΔMGlaciers - ΔMGreenland - ΔMAntarctica
- ΔMLand Waters - ΔMWater Vapor - ….
Closure of the sea level budget Global Mean Sea Level
- ∑ (thermal + mass) components = 0
Different Observing Systems
GRACE (2002-2017)
GRACE Follow-On (2018- )
High-precision altimeter satellites constellation
Argo
Bamber et al., ERL, 2018
Ice mass loss from the Greenland ice sheet (1993-2015)
Ice mass loss from the Antarctica ice sheet (1993-present)
IMBIE 2, 2018
Est
Peninsula
West Total Antarctica
Bilan du niveau de la mer 1993- présent
ESA Sea Level Budget Closure project
Niveau de la mer
observé
Somme des
composantes
Hausse de la mer observée = Somme des contributions
Niveau de la mer observé
Expansion thermique
+ Masse océan
2005-2016
WCRP Global Sea Level Budget group, 2018
Motivation to Assess the Global Mean Sea Level Budget
• Better understand processes at work and follow
temporal changes (acceleration?) of individual
components
• Place bounds on missing or poorly known
contributions (e.g., deep >2000m ocean warming not
sampled by Argo, …)
• Constrain the Earth’s energy imbalance
• Validate climate models used for projections
Shared Socioeconomic Pathways (SSPs)
The Shared Socioeconomic Pathways (SSPs) lead to a broad range in baselines (grey), with more aggressive mitigation leading to lower temperature outcomes (grouped by colours)
This set of quantified SSPs are based on the output of six Integrated Assessment Models (AIM/CGE, GCAM, IMAGE, MESSAGE, REMIND, WITCH). Net emissions include those from land-use change and bioenergy with CCS.
Source: Riahi et al. 2016; Rogelj et al. 2018; IIASA SSP Database; IAMC; Global Carbon Budget 2018
Future Sea Level Rise
Goodwin et al., 2018
T stabilization
What do we need
in terms of observing systems?
Observations of current changes are essential detect
accelerations, new regimes, runaway changes (tipping points)
process understanding and information to climate models
A long and accurate global and regional sea level record
sustained altimetry missions + continuing R&D activities to
improve the accuracy of the sea level record
Sustained/improved observing systems of all components
(ocean warming, ice sheets…) (Core Argo + Deep Argo, GRACE-
type missions for measuring mass changes, InSAR, …)
Constellation of high-precision altimetry missions
Courtesy: G. Dibarboure, CNES
Key questions related to sea level research (e.g., « Thriving on our changing Planet;
A decadal strategy for Earth Observation from Space,
The National Academies, 2018)
How much will sea level rise, globally and regionally, over
the next decade and beyond, in response to ice sheet mass
loss and ocean warming?
How will sea level change along the world coastlines?
10 km
Aujourd’hui on ne sait même pas répondre à la question:
« Le niveau de la mer à la côte monte-t-il à la même
vitesse qu’au large ? »
La hausse du niveau de la mer à la côte n’est pas juste une extrapolation de la hausse
au large certains phénomènes côtiers viennent se superposer à la hausse moyenne
globale et sa variabilité régionale (ex. courants côtiers, tendances des vagues, apport
d’eau douce par les rivières dans les estuaires, …)
Tendances régionales de la hausse de la mer (1992-2018)
ESA CCI+ Sea Level Project
Mesure de la hausse de la mer à la côte nouvelles études en cours
Corse
Portugal
Côte d’Ivoire
1.4 km
Niger River delta
Nigeria
Vertical Land Motions
max: 28 mm/yr max: 10 mm/yr max: 40 mm/yr
max: 150 mm/yr
max: 10 mm/yr max: 260 mm/yr
max: 40 mm/yr
max: 20 mm/yr
max: 10 mm/yr
Source: P. Teatini, ISSI workshop ‘Natural & Man-Made Hazards’, April 2019
What do we need in terms of observing systems?
To estimate ‘relative’ coastal sea level trends
worldwide
A global, multi-mission Coastal Altimetry data set
(retracking of all altimetry missions of the altimetry era
+ use of SAR altimetry on the Sentinel 3 missions;
explore GNSS reflectometry)
Vertical land motions (GNSS + InSAR)
What do we need in terms of observing systems?
To study causes and impacts of sea level rise on world
coastlines
Temperature and salinity measurements over shallow shelves
Coastal winds, waves and currents (multi-sensor approach)
River discharge in estuaries and deltas from current and future
altimetry techniques
Shoreline change monitoring by high-resolution imagery (SAR
and optical)
High-resolution DEM / Bathymetry using satellite imagery, lidar,
altimetry & other techniques
