W. Llovel

NASA · Jet Propulsion Laboratory

The ocean is the main heat reservoir in Earth’s climate system, absorbing most of the top-of-the-atmosphere excess radiation. As the climate warms, anomalously warm and fresh ocean waters in the densest layers formed near Antarctica spread northward through the abyssal ocean, while successions of warming and cooling events are seen in the deep-ocea...

Plain Language Summary Interannual variability of global mean sea level (GMSL) change is linked to natural climate modes of variability such as El Nino Southern Oscillation (ENSO). Over May 2014–June 2016, two consecutive El Nino events (warm phase of ENSO) occurred in the tropical Pacific ocean: one aborted in 2014–2015 and an extreme event in 201...

The estimation of the regional Ocean Heat Content (OHC) is essential for climate analysis and future climate predictions. In this study, we propose a method to estimate and propagate uncertainties in regional OHC changes. The OHC is estimated with space geodetic steric data corrected from salinity variations estimated with in situ measurements. A v...

The phytoplankton–light feedback (PLF) describes the interaction between phytoplankton biomass and the downwelling shortwave radiation entering the ocean. The PLF allows the simulation of differential heating across the ocean water column as a function of phytoplankton concentration. Only one third of the Earth system models contributing to the 6th...

Over the past few decades, the global mean sea level rise and superimposed regional fluctuations of sea level have exerted considerable stress on coastal communities, especially in low-elevation regions such as the Pacific Islands in the western South Pacific Ocean. This made it necessary to have the most comprehensive understanding of the forcing...

The phytoplankton-light feedback (PLF) depicts how phytoplankton biomass interacts with the downwelling shortwave radiation entering the ocean. Considering the PLF allows differential heating across the ocean water column as a function of the phytoplankton concentration. Only one third of the CMIP6 Earth system models include a complete representat...

Given the major role of the Atlantic Ocean in the climate system, it is essential to characterize the temporal and spatial variations of its heat content. The 4DATLANTIC-OHC project (2021-2023) aims at developing and testing space geodetic methods to estimate the local ocean heat content (OHC) changes over the Atlantic Ocean from satellite altimetr...

The global ocean is warming and has absorbed 90% of the Earth Energy Imbalance over 2010–2018 leading to global mean sea level rise. Both ocean heat content (OHC) and sea level trends show large regional deviations from their global means. Both quantities have been estimated from in-situ observations for years. However, in-situ profile coverage is...

Time-variable gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions have opened up a new avenue of opportunities for studying large-scale mass redistribution and transport in the Earth system. Over the past 19 years, GRACE/GRACE-FO time-variable gravity measurements have been widely us...

Plain Language Summary Variations in ocean bottom pressure reflect ocean mass redistribution and surface freshwater fluxes. The changes in ocean bottom pressure can be attributed to atmospherically driven signals and an oceanic intrinsic component, which is generated by the ocean itself and shows random and chaotic characteristics. While the former...

Plain Language Summary Sea level rise, due to the addition of meltwater from glaciers and ice‐sheets in the oceans and to the thermal expansion of seawater, is commonly used as an indicator for climate change. The sea level budget provides information on temporal changes in one or more components of the budget, on process understanding, on missing...

Satellite altimetry data have revealed a global mean sea level rise of 3.1 mm/yr since 1993 with large regional sea level variability. These remote data highlight complex structures especially in strongly eddying regions. A recent study showed that over 38% of the global ocean area, the chaotic variability may hinder the attribution to the atmosphe...

Global mean sea level has experienced an unabated rise over the 20th century. This observed rise is due to both ocean warming and increasing continental freshwater discharge. We estimate the net ocean mass contribution to sea level by assessing the global ocean salt budget based on the unprecedented amount of in situ data over 2005–2015. We obtain...

The Amazon River is by far the largest river by volume of water in the world, representing around 17% of the global riverine discharge to the oceans. Recent studies suggested that its impact on sea level is potentially important at global and regional scales. This study uses a set of regional simulations based on the ocean model NEMO to quantify th...

The observation and simulation of the variability of coastal sea level are impacted by various uncertainties, such as measurement errors and sampling biases, unresolved processes, and model and forcing biases. Ocean model simulations suggest that another uncertainty should be taken into account for the attribution of sea-level changes. Global ocean...

Community Paper - Frontiers of Marine Science https://www.frontiersin.org/articles/10.3389/fmars.2019.00432/full

The energy radiated by the Earth toward space does not compensate the incoming radiation from the Sun leading to a small positive energy imbalance at the top of the atmosphere (0.4–1 Wm–2). This imbalance is coined Earth’s Energy Imbalance (EEI). It is mostly caused by anthropogenic greenhouse gas emissions and is driving the current warming of the...

In the presence of mesoscale, the ocean spontaneously generates a strong Low Frequency Chaotic Intrinsic Variability (LFCIV). It locally competes with the atmospheric forcing in driving the interannual-to-multidecadal variability of key ocean climate indices (OHC, AMOC, MHT, etc). • Much weaker or absent in coarse-resolution ocean models used in mo...

A global 1/4° ocean/sea-ice 50-member ensemble simulation is analyzed to disentangle the imprints of the atmospheric forcing and the chaotic ocean variability on regional sea level trends over the satellite altimetry period. We find that the chaotic ocean variability may mask atmospherically-forced regional sea level trends over 38% of the global o...

Space altimetry has revolutionized physical oceanography by providing a continuous and global monitoring of the sea-surface height (SSH) for the last 25 years. The variability of this surface is accurately depicted over a wide range of scales, ranging from the size of mesocale structures (about 100km) to the scale of the Earth, with periods ranging...

A global 1/4∘ ocean/sea-ice 50-member ensemble simulation is used to disentangle the low-frequency imprints of the atmospherically-forced oceanic variability and of the chaotic intrinsic oceanic variability (IOV) on the large-scale (10° x10° ) ocean heat content (OHC) between 1980 and 2010. The IOV explains most of the interannual-to-decadal large-...

Evaluating global mean sea level (GMSL) in terms of its components—mass and steric—is useful for both quantifying the accuracy of the measurements and understanding the processes that contribute to GMSL rise. In this paper, we review the GMSL budget over two periods—1993 to 2014 and 2005 to 2014—using multiple data sets of both total GMSL and the c...

Since their launch in early 2002, the twin satellites of the Gravity Recovery and Climate Experiment (GRACE) have been providing global maps of Earth’s varying gravity field nearly continuously every month. The data record now spans more than 15 years of global surface mass change observations, allowing precise tracking of the redistribution and cy...

Evaluating global mean sea level (GMSL) in terms of its components—mass and steric—is useful for both quantifying the accuracy of the measurements and understanding the processes that contribute to GMSL rise. In this paper, we review the GMSL budget over two periods—1993 to 2014 and 2005 to 2014—using multiple data sets of both total GMSL and the c...

The climate system is gaining heat owing to increasing concentration of greenhouse gases due to human activities. As the world's oceans are the dominant reservoir of heat in the climate system, an accurate estimation of the ocean heat content change is essential to quantify the Earth's energy budget and global mean sea level rise. Based on the mean...

Steric sea level change has been identified as one of the major contributors to the regional variability of sea level trends observed by satellite altimetry for the past two decades. This contribution varies in space and time. The temperature (thermosteric) contribution to sea level has generally been found to be more important than the salinity (h...

A basin-wide mode of ocean bottom pressure and sea level fluctuation is identified across the Arctic Ocean and the Nordic Seas using satellite and in situ observations in conjunction with a global ocean circulation model and its adjoint. The variation extends across the interconnected deep ocean basins of these semi-enclosed Arctic seas, collective...

As the dominant reservoir of heat uptake in the climate system, the world/'s oceans provide a critical measure of global climate change. Here, we infer deep-ocean warming in the context of global sea-level rise and Earth/'s energy budget between January 2005 and December 2013. Direct measurements of ocean warming above 2,000 m depth explain about 3...

There is no robust evidence for warming of the global upper ocean and an associated sea-level rise based on a nearly global and continuous data coverage of the surface and upper ocean. The amount of sea level change contributed by the deep ocean is unclear, however, because of limited data availability below 2000 m. The Bermuda Atlantic Time-series...

The dependency of global mean thermosteric sea level changes to temperature at different depths down to 700 m is investigated from 1960 to 2010 using two separate gridded temperature datasets, and compared with reconstructed estimates of sea level change. The rates of thermosteric sea level changes are closely correlated with those of reconstructed...

Interannual global mean sea level (GMSL) variations and El Nino-Southern Oscillation (ENSO) are highly correlated, with positive/negative GMSL anomalies during El Nino/La Nina events. In a previous study, we showed that interannual GMSL and total land water storage variations are inversely correlated, with lower-than average total water storage on...

We compare different past sea level reconstructions over the 1950–2009 time span using the Empirical Orthogonal Function (EOF) approach. The reconstructions are based on 91 long (up to 60 years) but sparsely distributed tide-gauge records and gridded sea level data from two numerical ocean models over 1958–2007 (the DRAKKAR/NEMO model without data...

We investigate sea level change and variability in some areas of the Arctic region over the 1950-2009 period. Analysis of 62 long tide gauge records available during the studied period along the Norwegian and Russian coastlines shows that coastal mean sea level (corrected for Glacial Isostatic Adjustment and inverted barometer effects) in these two...

We investigate the spatio-temporal variability of sea level trend patterns observed by satellite altimetry since 1993, focusing on the Tropical Pacific. The objective of this study is two fold. On the basis of a 2-D past sea level reconstruction (over 1950–2009) – based on a combination of observations and ocean modelling – and multi-century contro...

Outre une hausse moyenne de l'ordre de 3 mm par an, le niveau moyen global de la mer présente des fluctuations de quelques millimètres durant les événements El Niño et La Niña. Lors de El Niño, on observe une anomalie positive alors qu'à La Niña correspond une anomalie négative du niveau de la mer. Ces fluctuations du niveau moyen global de la mer...

The western tropical Pacific is usually considered as one of the most vulnerable regions of the world under present-day and future global warming. It is often reported that some islands of the region already suffer significant sea level rise. To clarify the latter concern, in the present study we estimate sea level rise and variability since 1950 i...

We investigate the spatio-temporal variability of sea level trend patterns observed by satellite altimetry since 1993, focusing on the Tropical Pacific. The objective of this study is two fold. On the basis of a 2-D past sea level reconstruction (over 1950–2009) – based on a combination of observations and ocean modelling – and multi-century contro...

We investigate the spatio-temporal variability of sea level trend patterns observed by satellite altimetry since 1993, focusing on the tropical Pacific. The objective of this study is two fold. On the basis of a past 2-D sea level reconstruction (over 1950-2009) -based on observations- and multi-century control runs from an ensemble of 8 CMIP3 coup...

We investigate sea level change and variability in the Arctic region over the 1950-2009 time span. Analysis of >60 long tide gauge records available since 1950 along the Norwegian and Russian sectors shows that coastal mean sea level was almost stable until about 1980 but since then displayed a clear increasing trend. In fact until the mid-1990s, t...

We investigate the regional-ocean depth layer (down to 2000 m) contributions to global mean steric sea level from January 2004 to March 2010, using Argo-based ocean temperature and salinity data from the SCRIPPS Oceanographic Institution database. We find that Indian ocean warming is almost compensated by Atlantic ocean cooling, so that the total g...

Two-dimensional reconstructions of the Mediterranean sea level corrected for the atmospheric effects are proposed at monthly interval over the period 1970–2006 using 14 tide gage records and 33-year long (1970–2002) sea level grids from the NEMOMED8 regional ocean circulation model (NM8) and the PROTHEUS System Atmosphere–Ocean coupled model (PS)....

The contributing factors to regional sea level variability have been explored for the period 2004–2008 based on altimetry observations, hydrographic data and GRACE measurements. The regional averaged annual cycle of the mass contribution to sea level is shown to be highly unsteady. When compared with steric-corrected altimetry, both signals are coh...

Snow volume change over the 1989/2006 period has been derived from Special Sensor Microwave/Imager (SSM/I) radiometric measurements for all land surfaces above 50°N, except Greenland. The mean annual snow volumes over the whole study domain, Eurasia and North America are respectively equal to 3713 km3, 2272 km3 and 1441 km3, for the Pan Arctic regi...

On decadal to multidecadal time scales, thermal expansion of sea waters and land ice loss are the main contributors to sea level variations. However, modification of the terrestrial water cycle due to climate variability and direct anthropogenic forcing may also affect sea level. For the past decades, variations in land water storage and correspond...

Tide gauge records suggest a rise in sea level rise of ~1.8 mm/yr over the 20st century. More recently, satellite altimetry data reveal a global mean sea level rise of 3.3 mm/yr over 1993-2010. This rise is attributed to Earth's global warming observed since several decades. In this thesis, we analyze observed global mean sea level and its causes o...

In the recent years, the land ice contribution to sea level has significantly increased. For example, during the 1993-2003 time span, land ice loss from ice sheets and glaciers contributed to sea level rise by ~ 40%, most of the remaining being due to ocean warming. However since 2003, ocean thermal expansion has increased less rapidly. Besides, nu...

For the last two decades, steric sea level is one of the major contributions of the observed sea level rise (Bindoff et al, 2007). This contribution is not steady and varies with time both globally and regionally. Different estimations, based on different analyses and computing strategies of in situ hydrographic data, conclude to substantial global...

Satellite altimetry has revealed important regional variability in sea level trends for the past >15 years. Ocean re analyses available for the past 4-5 decades also display non uniform spatial trend patterns in sea level, significantly different than those observed over the last 15 years. In situ hydrographic measurements and ocean general circula...

Sea level rise is a major consequence of global warming, which threatens many low-lying, highly populated coastal regions of the world. In such regions, sea level rise amplifies other stresses due to natural phenomena (e.g., sediment load-induced ground subsidence in deltaic areas, vertical ground motions due to tectonics, volcanism and post-glacia...

In this study, we have estimated the different sea level components (observed sea level from satellite altimetry, steric sea level from in situ hydrography—including Argo profiling floats, and ocean mass from Gravity Recovery and Climate Experiment; GRACE), in terms of regional and interannual variability, over 2002–2009. We compute the steric sea...

We investigate the interannual variability over 2003–2008 of different hydrological parameters in the Amazon river basin: (1) vertically-integrated water storage from the GRACE space gravimetry mission, (2) surface water level of the Amazon River and its tributaries from in situ gauge stations, and (3) precipitation. We analyze the spatio-temporal...

For the past decades, there are no direct basin-scale sea level observations concerning the spatial sea level patterns and their evolution in the Mediterranean Sea. In order to understand physical processes driving sea level variability it is important to know the dominant modes of regional variability on interannual/decadal/multidecadal time scale...

Using outputs of a 56-yr long (1950-2006) run of the ISBA/TRIP hydrological model developed at CNRM/MeteoFrance, forced by atmospheric data, we have estimated the terrestrial water storage (TWS) contribution to the global mean sea level. We focus on interannual to multidecadal time scales. At interannual time scale, global TWS produces global mean...

Satellite altimetry has revealed important regional variability in sea level trends for the past >15 years. Ocean re-analyses available for the past 4-5 decades also display non uniform spatial trend patterns in sea level, significantly different than those observed over the last 15 years. In situ hydrographic measurements and ocean general circula...

ABSTRACT

We have jointly analysed space gravimetry data from the GRACE space mission, satellite altimetry data and precipitation over the East African Great Lakes region, in order to study the spatiotemporal variability of hydrological parameters (total water storage, lake water volume and rainfall). We find that terrestrial water storage (TWS) from GRACE a...

Global change in land water storage and its effect on sea level is estimated over a 7-year time span (August 2002 to July 2009) using space gravimetry data from GRACE. The 33 World largest river basins are considered. We focus on the year-to-year variability and construct a total land water storage time series that we further express in equivalent...

Measuring sea level change and understanding its causes has considerably improved in the recent years, essentially because new in situ and remote sensing observations have become available. Here we report on most recent results on contemporary sea level rise. We first present sea level observations from tide gauges over the twentieth century and fr...

Global change in land water storage and its effect on sea level is estimated over a 7-year time span (August 2002 to July 2009) using space gravimetry data from GRACE. The 33 World largest river basins are considered. We focus on the year-to-year variability and construct a total land water storage time series that we further express in equivalent...

Au cours du 20ème} siècle, les enregistrements marégraphiques suggèrent une hausse du niveau de la mer de 1.8 mm/an. Plus récemment, les observations spatiales indiquent une hausse de 3.3 mm/an sur la période 1993-2009. Cette augmentation au cours du temps est attribuée au réchauffement global de la planète enregistré depuis plusieurs années mainte...

Future sea level projections for 2100 from IPCC AR4 indicate significant regional variability around the global mean rise. Important regional variability in rates of sea level rise has been observed by satellite altimetry for the past 17 years, highly correlated with non uniform thermal expansion. Sea level reconstructions for the past 50 years als...

The global mean sea level budget over 2003-2008 was studied in a few recent papers using satellite altimetry, Argo and GRACE observations. Here we investigate the regional variability in sea level over the same period and the same data sets. Spatial patterns in observed (from satellite altimetry) and steric (from Argo) sea level agree quite well ov...

For the past decades, there are no direct basin-scale observations informing on the spatial trend patterns in Mediterranean sea level. Yet it is important to know the dominant modes of regional variability on interannual/decadal/multidecadal time scale in the Mediterranean basin and their driving mechanisms. For that purpose, we have developed a re...

Global change in land water storage and its effect on sea level is estimated over a 6-year time span (mid-2002 to mid-2008) using satellite altimetry and space gravimetry data from GRACE. Satellite altimetry allows determination of surface water volume change while GRACE data provide vertically-integrated water storage change. The 32 largest river...

We have jointly analysed space gravimetry data from the GRACE space mission, precipitation and satellite altimetry data over the East African Great Lakes region, in order to study the spatio-temporal variability of hydrological changes. We find that precipitation and terrestrial water storage (TWS) from GRACE show a common mode of variability at in...

A two-dimensional reconstruction of past sea level is proposed at yearly interval over the period 1950-2003 using tide gauge records from 99 selected sites and 44-year long (1960-2003) 2°×2° sea level grids from the OPA/NEMO ocean general circulation model with data assimilation. We focus on the regional variability and do not attempt to compute th...

Future sea level projections for 2100 from IPCC AR4 indicate significant regional variability around the global mean rise. Important regional variability in rates of sea level rise has been observed by satellite altimetry for the past 15 years, highly correlated with non uniform thermal expansion. Sea level reconstructions for the past 50 years als...

Over the past five years (2003-2008), ocean thermal expansion based on the newly deployed Argo system shows a much lower increase than during the 1993-2003 decade (~0.3 mm/yr compared to ~1.5 mm/yr). The cause of the recent pause in thermal expansion is not yet understood. However, during the 2003-2008 time span, altimetry-based sea level was still...