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ArticleMeasuring global ocean heat content to estimate the Earth energy Imbalance(Frontiers Media, 2019-08-20) Meyssignac, Benoit ; Boyer, Tim ; Zhao, Zhongxiang ; Hakuba, Maria Z. ; Landerer, Felix ; Stammer, Detlef ; Kohl, Armin ; Kato, Seiji ; L’Ecuyer, Tristan S. ; Ablain, Michaël ; Abraham, John Patrick ; Blazquez, Alejandro ; Cazenave, Anny ; Church, John A. ; Cowley, Rebecca ; Cheng, Lijing ; Domingues, Catia M. ; Giglio, Donata ; Gouretski, Viktor ; Ishii, Masayoshi ; Johnson, Gregory C. ; Killick, Rachel E. ; Legler, David ; Llovel, William ; Lyman, John ; Palmer, Matthew D. ; Piotrowicz, Stephen R. ; Purkey, Sarah G. ; Roemmich, Dean ; Roca, Rémy ; Savita, Abhishek ; von Schuckmann, Karina ; Speich, Sabrina ; Stephens, Graeme ; Wang, Gongjie ; Wijffels, Susan E. ; Zilberman, NathalieThe 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 planet. Precise monitoring of EEI is critical to assess the current status of climate change and the future evolution of climate. But the monitoring of EEI is challenging as EEI is two orders of magnitude smaller than the radiation fluxes in and out of the Earth system. Over 93% of the excess energy that is gained by the Earth in response to the positive EEI accumulates into the ocean in the form of heat. This accumulation of heat can be tracked with the ocean observing system such that today, the monitoring of Ocean Heat Content (OHC) and its long-term change provide the most efficient approach to estimate EEI. In this community paper we review the current four state-of-the-art methods to estimate global OHC changes and evaluate their relevance to derive EEI estimates on different time scales. These four methods make use of: (1) direct observations of in situ temperature; (2) satellite-based measurements of the ocean surface net heat fluxes; (3) satellite-based estimates of the thermal expansion of the ocean and (4) ocean reanalyses that assimilate observations from both satellite and in situ instruments. For each method we review the potential and the uncertainty of the method to estimate global OHC changes. We also analyze gaps in the current capability of each method and identify ways of progress for the future to fulfill the requirements of EEI monitoring. Achieving the observation of EEI with sufficient accuracy will depend on merging the remote sensing techniques with in situ measurements of key variables as an integral part of the Ocean Observing System.
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ArticleDesigning coastal adaptation strategies to tackle sea level rise(Frontiers Media, 2021-11-03) Bongarts Lebbe, Théophile ; Rey-Valette, Hélène ; Chaumillon, Éric ; Camus, Guigone ; Almar, Rafael ; Cazenave, Anny ; Claudet, Joachim ; Rocle, Nicolas ; Meur-Férec, Catherine ; Viard, Frédérique ; Mercier, Denis ; Dupuy, Christine ; Ménard, Frédéric ; Rossel, Bernardo Aliaga ; Mullineaux, Lauren S. ; Sicre, Marie-Alexandrine ; Zivian, Anna ; Gaill, Francoise ; Euzen, AgatheFaced with sea level rise and the intensification of extreme events, human populations living on the coasts are developing responses to address local situations. A synthesis of the literature on responses to coastal adaptation allows us to highlight different adaptation strategies. Here, we analyze these strategies according to the complexity of their implementation, both institutionally and technically. First, we distinguish two opposing paradigms – fighting against rising sea levels or adapting to new climatic conditions; and second, we observe the level of integrated management of the strategies. This typology allows a distinction between four archetypes with the most commonly associated governance modalities for each. We then underline the need for hybrid approaches and adaptation trajectories over time to take into account local socio-cultural, geographical, and climatic conditions as well as to integrate stakeholders in the design and implementation of responses. We show that dynamic and participatory policies can foster collective learning processes and enable the evolution of social values and behaviors. Finally, adaptation policies rely on knowledge and participatory engagement, multi-scalar governance, policy monitoring, and territorial solidarity. These conditions are especially relevant for densely populated areas that will be confronted with sea level rise, thus for coastal cities in particular.
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ArticleTowards comprehensive observing and modeling systems for monitoring and predicting regional to coastal sea level(Frontiers Media, 2019-07-25) Ponte, Rui M. ; Carson, Mark ; Cirano, Mauro ; Domingues, Catia M. ; Jevrejeva, Svetlana ; Marcos, Marta ; Mitchum, Gary ; van de Wal, Roderik S.W. ; Woodworth, Philip L. ; Ablain, Michaël ; Ardhuin, Fabrice ; Ballu, Valerie ; Becker, Mélanie ; Benveniste, Jérôme ; Birol, Florence ; Bradshaw, Elizabeth ; Cazenave, Anny ; De Mey-Frémaux, Pierre ; Durand, Fabien ; Ezer, Tal ; Fu, Lee-Lueng ; Fukumori, Ichiro ; Gordon, Kathy ; Gravelle, Médéric ; Griffies, Stephen M. ; Han, Weiqing ; Hibbert, Angela ; Hughes, Chris W. ; Idier, Deborah ; Kourafalou, Vassiliki H. ; Little, Christopher M. ; Matthews, Andrew ; Melet, Angelique ; Merrifield, Mark ; Meyssignac, Benoit ; Minobe, Shoshiro ; Penduff, Thierry ; Picot, Nicolas ; Piecuch, Christopher G. ; Ray, Richard D. ; Rickards, Lesley ; Santamaría-Gómez, Alvaro ; Stammer, Detlef ; Staneva, Joanna ; Testut, Laurent ; Thompson, Keith ; Thompson, Philip ; Vignudelli, Stefano ; Williams, Joanne ; Williams, Simon D. P. ; Wöppelmann, Guy ; Zanna, Laure ; Zhang, XuebinA major challenge for managing impacts and implementing effective mitigation measures and adaptation strategies for coastal zones affected by future sea level (SL) rise is our limited capacity to predict SL change at the coast on relevant spatial and temporal scales. Predicting coastal SL requires the ability to monitor and simulate a multitude of physical processes affecting SL, from local effects of wind waves and river runoff to remote influences of the large-scale ocean circulation on the coast. Here we assess our current understanding of the causes of coastal SL variability on monthly to multi-decadal timescales, including geodetic, oceanographic and atmospheric aspects of the problem, and review available observing systems informing on coastal SL. We also review the ability of existing models and data assimilation systems to estimate coastal SL variations and of atmosphere-ocean global coupled models and related regional downscaling efforts to project future SL changes. We discuss (1) observational gaps and uncertainties, and priorities for the development of an optimal and integrated coastal SL observing system, (2) strategies for advancing model capabilities in forecasting short-term processes and projecting long-term changes affecting coastal SL, and (3) possible future developments of sea level services enabling better connection of scientists and user communities and facilitating assessment and decision making for adaptation to future coastal SL change.