Leveraging the need for indicators: An Outline Report (D3.4)

1 Deliverable D3.4 Leveraging the need for indicators: An Outline Report D 3.4 Leveraging the need of indicators: An Outline Report 2 DELIVERABLE Deliverable D3.4 Leveraging the need for indicators: An Outline Report Version Version 2 of 9 December 2025 Work Package WP3 EOV - based ocean indicators for climate Due Date 30 April 2025 Submission Date 23 April 2025 Submission Date Version 2 9 December 2025 Changes introduced: Integration of the last publication in the list of the References, since the paper has been published. Dissemination Level Public (PU) Deliverable Lead Maynooth University (NUIM) Authors Samantha Hallam ([email protected]) Karina Von Schuckmann (MOI) Ronan McAdam (CMCC) Gerard McCarthy (gerard[email protected]) Contributors Pia Englyst (DMI) Roshin. P. Raj (NERSC) Karin Margretha H. Larsen (HAV) Reviewer Chiara Bearzotti (DMI) DISCLAIMER Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Executive Agency (REA). Neither the European Union nor the granting authority can be held responsible for them . D 3.4 Leveraging the need of indicators: An Outline Report 3 TABLE OF CONTENTS 1. Publishable summary 4 2. Introduction 5 2.1 Introduction to climate and ocean indicators 5 2.2. Why do we need ocean indicators 6 2.3 Requirements of an ocean indicator 10 3. Regionalisation of Ocean Indicators 11 3.1 The need for regionalised ocean indicators 11 3.2 Process of Agreement 11 3.3 Agreed regions and proposed indicators 12 3.3.1 Sea Surface Temperature and Sea Ice Temperature 14 3.3.2 Subsurface Temperature 17 3.3.3 Sea Ice 18 3.3.4 Sea Surface Height 23 3.4 Examples of Regionalisation 24 3.4.1 Irish SST 24 3.4.2 Using IST vs UISST (Under Ice SST) 24 4. Extreme Indicators 25 4.1 The need for extreme indicators 25 4.2 Process of Agreement 26 4.3 Towards a framework for extreme indicators 30 5. Contribution to the ObsSea4Clim objectives 32 6. References 32 D 3.4 Leveraging the need of indicators: An Outline Report 4 1. Publishable summary Global climate indicators are used to describe and monitor the state of the climate. Five of the seven ‘state-of-the-climate’ indicators used by the World Meteorological Organisation relate to the ocean, highlighting the significant impact of the ocean on the climate, including ocean surface temperature, sea level, ocean heat content, sea ice extent, and ocean acidification. The ObsSea4Clim project focuses on physical ocean indicators, which are crucial for climate understanding. Ocean indicators are necessary as they transform complex ocean data into simple and useful measures of the ocean's state and climate, which, combined with science-based knowledge, can inform policymakers and other stakeholders, ultimately supporting decision-making for a sustainable future and benefiting both society and the economy. Six science-based quality criteria have been identified that ocean indicators should have: verified, significant, scalable, justified, measurable, and accessible. Indicators should be expertly assessed against these criteria to establish if they are scientifically mature and ready for implementation. This will help ensure the scientific robustness. One of the challenges in ObsSea4Clim is to define the proposed ocean indicators for the Essential Ocean Variables (EOVs) such as sea surface temperature (SST), subsurface temperature, sea surface height, and sea ice and to regionalise the indicators. Regionalised ocean indicators help understanding which regions exhibit unique oceanic and climatic patterns, the factors driving these patterns, and how they relate to global trends. For each proposed ocean indicator, the regions were identified, including both the global perspective, where relevant, and then progressively smaller regions and seas. Thematic regions are also included for some indicators. Legislative exclusive economic zones (EEZ) will be analysed in specific case studies. For each ocean indicator, the proposed measures and associated data have been identified and will now be analysed on a regionalised basis and tested as part of the project for scientific robustness by the relevant lead institution in each case. D 3.4 Leveraging the need of indicators: An Outline Report 5 Extreme ocean indicators have also been identified. An extreme event in the ocean occurs when a physical or biogeochemical variable crosses a threshold that has a tangible impact on a physical process, ecosystem health, or the economy. Three target extremes have been identified: extreme temperature (or marine heatwaves - MHWs), extreme sea ice and extreme sea level. A key conclusion of the discussions has been to promote the testing of several definitions for each of the extreme indicators rather than attempt to find one universal indicator. Accordingly, the ongoing work within the project will promote a framework for extreme indicator definition, in which key parameters and characteristics can be chosen on a case-by-case basis. 2. Introduction 2.1 Introduction to climate and ocean indicators Global climate indicators are key parameters used to describe and monitor the changing climate, e.g. https://climatedata-catalogue-wmo.org/climate_indicators. They provide a picture of the state of the climate system and help track climate change across different domains. The WMO uses 7 ‘state-of-the-climate’ indicators that are based on the 54 Global Climate Observing System (GCOS) Essential Climate variables. 5 of the 7 ‘state-of-the-climate’ indicators are ocean indicators, highlighting the fundamental impact of the ocean on climate; ocean surface temperature, sea level, ocean heat content, sea ice extent and ocean acidification and considered the core ocean indicators for assessing the state of the climate D 3.4 Leveraging the need of indicators: An Outline Report 6 Fig. 1: WMO ‘State-of-the-climate’ indicators, Ref: https://climatedata-cataloguewmo.org/climate_indicators The project scope for ObsSea4Clim covers the physical ocean indicators (Ocean Heat, Sea level and Sea Ice) whilst the sister projects BioEcoOcean and BioGeoSea cover biological and geochemical ocean indicators respectively. 2.2. Why do we need ocean indicators Ocean indicators take complex ocean data and turn it into simple and useful measures of the state of the ocean and climate. They are a useful tool for regular reporting on the state, variability and change of the ocean and help forge multi-disciplinary collaboration. The ocean indicators together with science-based knowledge help inform effective decision making and beyond (von Schuckmann et al., 2020). Ocean indicators are a powerful tool to establish a dialogue at the science policy interface, in support of decision making and for sustainable development. D 3.4 Leveraging the need of indicators: An Outline Report 7 Fig. 2: The role of ocean monitoring and reporting to support and provide benefits to society and the economy. From von Schuckmann et al., 2020, J. of Marine Policy. Figure 2 highlights the role of ocean monitoring and reporting and the added-value chain from raw products (remote sensing, in situ) to oceanographic science knowledge (including models) to high-quality data products and ocean indicators, which are used for reporting. These added-value products can provide the evidence basis for agencies and reporting bodies, decision makers, other stakeholders and the public, yielding societal and economic benefit (von Schuckmann et al., 2020). D 3.4 Leveraging the need of indicators: An Outline Report 8 Fig. 3: The need for ocean indicators. Providing more detail, Figure 3 highlights the 8 core areas where ocean indicators can add value. ● Observing system capacity: For example, our observing capacity is good for sea surface temperature in the North Atlantic, but not as good at subsurface temperature at 2000m in the Southern Ocean. ● Forecast and Model: Ocean indicators can assist with model validation and forecasting accuracy ● Ocean and climate assessments and reporting: Focusing on the same indicators over time and specific regions helps to build up a coherent and comprehensive picture of how the ocean and climate health is changing. ● Ocean literacy and communication: Focusing consistently on key ocean indicators will help to build society’s knowledge of the ocean, ocean health, and the important role the ocean plays in climate. ● Ocean climate nexus and governance: Focus on the key ocean indicators which influence climate will help to provide focus in this complex area. ● International and multi-to-transdisciplinary collaboration: For example, the blue economy plays an essential role in supporting society. SST is used for coastal fisheries and coral reef management and sub-surface D 3.4 Leveraging the need of indicators: An Outline Report 9 temperature is linked to marine organisms and ecosystem function. A transdisciplinary approach to monitoring oceanographic data is very helpful in the management of living marine resources. ● Research priority areas: Ocean indicators help to highlight research gaps that may become areas of research focus, such as the subpolar gyre warming hole in the North Atlantic. D 3.4 Leveraging the need of indicators: An Outline Report 16 Table 2: Variables and Regions associated with Sea Ice Surface Temperature. EOV/ECV Indicator Measure Data Timeframe Regions and ObsSea4Clim partner in lead Sea Ice Surface temperature Sea Ice Surface Temperature Mean IST AASTI/C3S L3/L4 [DMI] 1982 - present Arctic/Antarctic sea ice [DMI] neXtSIM reanalysis, Copernicus datasets 1996 - present Arctic [NERSC] Sea Ice Surface temperature Melt Days Days when the mean temperature is 0 °C or warmer AASTI/C3S L3/L4 [DMI] 1982 - present Arctic/Antarctic sea ice [DMI] Sea Ice Surface temperature Freezing degree days (FDD) The cumulative FDD is usually calculated as a sum of average daily degrees below freezing AASTI/C3S L3/L4 [DMI] 1982 - present Arctic/Antarctic sea ice [DMI] D 3.4 Leveraging the need of indicators: An Outline Report 17 3.3.2 Subsurface Temperature Table 3: Variables and Regions associated with Subsurface Temperature. EOV Indicator Measure Data Timeframe Regions Subregions Case Studies and ObsSea4Clim partner in lead Subsurface Temperature Ocean Heat Content Ocean Heat Content Copernicus reanalysis - global and regional 1980 - present (satellite) NE Atlantic Ocean and adjacent seas [MOI] North Atlantic [MOI] Global [MOI and others] Mediterranean [MOI] Barents Sea [NERSC] Black Sea[MOI] Baltic [MOI] IBI [MOI] Nordic[DMI, HAV] NWS[MOI} MDR [NUIM] Gulf Stream/AMOC and Atlantic OHC [NUIM] Subsurface Temperature Marine Heatwaves Subsurface Temperatures Copernicus reanalysis - regional 1982 - present Mediterranean Sea [CMCC] Subsurface marine heatwaves 1993 - present Baltic Sea [FMI Barents Sea [NERSC] *precise definition of subsurface MHWs (e.g. using OHC) will be dependent on the findings of 3.2. D 3.4 Leveraging the need of indicators: An Outline Report 18 3.3.3 Sea Ice Table 4: Variables and Regions associated with Sea Ice Concentration. EOV Indicator Measure Data Timeframe Regions / Subregion and ObsSea4Clim partner in lead Sea Ice Sea Ice Concentration Satellitederived sea ice concentration OSI-450a Global Sea Ice Concentration climate data record (SMMR/SSMI/SSMIS), release 3 OSI-458 Global Sea Ice Concentration climate data record (AMSR), release 3 ESA Sea Ice CCI: High(er) Resolution Sea Ice Concentration CDR, v3 NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, Version 4 1978-present (incl iCDR) 2002-present (incl iCDR) 1991-2020 1979-present Arctic and Antarctic sea Ice [DMI] neXtSIM reanalysis Copernicus Marine Services 1996-present Arctic and Antarctic sea Ice [NERSC] D 3.4 Leveraging the need of indicators: An Outline Report 19 Satellite Passive microwave Global Sea Ice Concentration climate data record (SMMR/SSMI/SSMIS) and NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, Version 4 (1979 onwards) 1978-present Antarctic Sea Ice [NCPOR] SAR Sentinel-radar backscatter (2014) and EOS-04 RISAT-1 radar backscatter(2012) Available images from 2014 Antarctic Sea Ice [NCPOR] Global reanalysis ensemble product Copernicus Marine Services 1993-present Arctic and Antarctic [CMCC] Satellite-derived SIC from NOAA/NSIDC CDR, OSI SAF, ESA, CCI 1979present/2002-2017 Arctic and Antarctic [CMCC] EOV Indicator Measure Data Timeframe Regions / Subregion and ObsSea4Clim partner in lead Sea Ice Sea Ice Extent Satellite passive microwave OSI - SAF version 3, Global Sea Ice Concentration climate data record (SMRR, SSMI, SSMIS) NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice concentration, version 4 1978/9 - present Antarctic sea ice [NCPOR] Satellite Arctic OMI SI extent obs, satellite observations 1979 - present(satellite) Arctic and Antarctic [MOI] D 3.4 Leveraging the need of indicators: An Outline Report 20 derived; ocean reanalysis and forecast OSI SAF Sea ice index 1978 - onwards, version 2.2 (2023), OSI - 420. EUMETSAT Ocean and Sea Ice Satellite Application Facility. Antarctic_OMI_SI_extent_obs, satellite observations OSI SAF Sea ice index 1978-onwards, version 2.2 (2023), OSI-420. EUMETSAT Ocean and Sea Ice Satellite Application Facility. GLOBAL_MULTIYEAR_PHY_001_030, numerical models & GLOBAL_ANALYSISFORECAST_PHY_001_024 1993-present (forecast and reanalysis) Satellite - derived OSI - 450a Global Sea Ice Concentration climate data record (SMMR/SSMI/SSMIS), release 3 OSI-458 Global Sea Ice Concentration climate data record (AMSR), release 3 ESA Sea Ice CCI: High(er) Resolution Sea Ice Concentration CDR, v3 NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, Version 4 1978 - present (incl iCDR) 2002-present (incl iCDR) 1991-2020 1979-present Arctic and Antarctic sea ice [DMI] D 3.4 Leveraging the need of indicators: An Outline Report 21 Table 5: Variables and Regions associated with other Sea Ice Indicators. EOV Indicator Measure Data Timeframe Regions / Subregion and ObsSea4Clim partner in lead Sea Ice Sea Ice Drift neXtSIM reanalysis Copernicus Marine Services 1996-present Arctic [NERSC] Buoy International Arctic Buoy Programme (IABP) 1979 - present Arctic [FMI] Satellite Passive Microwave Global Sea Ice Concentration climate data record (SMMR/SSMI/SSMIS) 1978-present Antarctic sea ice [NCPOR] SAR Sentinel-radar backscatter EOS-04, RISAT-1 radar backscatter Available images since 2014 Available images since 2012 Antarctic sea ice [NCPOR] Satellite passive microwave NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, Version 4 1979-present Antarctic sea ice [NCPOR] Sea Ice Sea Ice thickness In - situ observatio ns FMI monitoring programme 1898-present Baltic/Bay of Bothnia [FMI] Global reanalysis Copernicus Marine Services 1993-present Arctic and Antarctic [CMCC] D 3.4 Leveraging the need of indicators: An Outline Report 22 EOV Indicator Measure Data Timeframe Regions / Subregion and ObsSea4Clim partner in lead Sea Ice Sea Ice Age Satellite Derived and neXtSIM reanalysis Copernicus Marine Services 1996 - present Arctic [NERSC] Sea Ice Sea Ice Area Satellite Passive Microwave Global Sea Ice Concentration climate data record (SMMR/SSMI/SSMIS) and NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, Version 4 1978 - present Antarctic Sea Ice [NCPOR Synthetic Aperture Radar (SAR) Sentinel-radar backscatter EOS-04, RISAT-1 radar backscatter Available images from 2012 and 2014 Antarctic Sea Ice [NCPOR Sea Ice Area/ Freezeup/Break update/ Open water days Satellite - derived OSI - 450a Global Sea Ice Concentration climate data record (SMMR/SSMI/SSMIS), release 3 OSI-458 Global Sea Ice Concentration climate data record (AMSR), release 3 ESA Sea Ice CCI: High(er) Resolution Sea Ice Concentration CDR, v3 NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, Version 4 1978 - present (incl iCDR) 2002-present (incl iCDR) 1991-2020 1979-present Arctic and Antarctic sea ice [DMI] D 3.4 Leveraging the need of indicators: An Outline Report 23 Sea Ice Freezing Date/ Break update In - situ observations FMI monitoring programme 1898 - present Baltic/Bay of Bothnia Sea Ice Sea Ice Volume neXtSIM Copernicus Marine Services 1996 - present Arctic [NERSC] D 3.4 Leveraging the need of indicators: An Outline Report 24 3.3.4 Sea Surface Height Table 6: Variables and Regions associated with Sea Surface Height. EOV Indicator Measure Data Timeframe Regions Subregions Case Studies and ObsSea4Clim partner in lead Sea Surface Height Sea Level Mean Sea Level Copernicus Satellite Observations and Reanalysis 1980 - present 1950-present 1993-present NE Atlantic Oceans and adjacent seas [MOI] Nordic and Barents Seas Mediterranean [MOI] Barents Sea [NERSC] Black Sea [MOI], Baltic[MOI] IBI[MOI], Nordic[HAV, DMI], NWS[MOI] Coastlines e.g.national/ regional Link between data e.g. Irish [NUIM] Sea Surface Height Sea level Mass Component GRACE GRACE/FO 2002 - 2017 2018-present Global Norwegian Continental shelf [NERSC] Arctic Ocean [NERSC] Quantify open ocean contribution Norwegian sea level variations Sea Surface Height In - situ Sea Level Tide Gauge Monthly tide gauge data (PSMSL) 1800 - present (but not complete) Global coastline Arctic Ocean Assess the quality of the Arctic Ocean Physics reanalysis Topaz4b 10 minute tide gauge data (Kartverket) late 1980s - present (but not complete) Norwegian Coast Western and Central Norway 1) Assess the quality of satellite altimetry products (e.g., SWOT). 2) Characterize mesoscale variability over the Norwegian continental shelf D 3.4 Leveraging the need of indicators: An Outline Report 25 3.4 Examples of Regionalisation 3.4.1 Irish SST Figure 7 shows the mean SST from 1982-2024 for the NE Atlantic, full Irish Continental Shelf Waters and Irish EEZ. Whilst the variability is fairly consistent between the areas over the time period, the territorial waters are up to 0.5°C warmer than the NE Atlantic over the period. The difference in temperature can be important for the location of fish species and when comparing across different data products. Fig. 7: Annual Mean SST 1982-2024. North Eastern Atlantic (blue), Irish Territorial Waters (Green), Irish EEZ (red). Data NOAA OISST. 3.4.2 Using IST vs UISST (Under Ice SST) Traditionally, sea surface temperature (SST) trends have been estimated only for the extra-polar (60°S – 60°N) ocean or globally using under-ice SSTs (UISST) in sea-ice covered regions. The UISST represents a proxy estimate of the water temperature just below the sea ice (usually assumed to be at the freezing point of sea water, ~ -1.8°C), and does not represent the actual surface temperature of the sea ice. The SST/UISST is thus a very poor indicator of the surface temperature changes in high latitudes. A more accurate and consistent way to monitor high-latitude surface temperature changes can D 3.4 Leveraging the need of indicators: An Outline Report 32 5. Contribution to the ObsSea4Clim objectives This deliverable contributes to the achievement of the following specific objectives of the project. #SO1 To develop ocean indicators, provide improved EOV/ECVs and evolve European ocean observing Ocean indicators are necessary as they transform complex ocean data into simple and useful measures of the ocean's state and climate, which, combined with sciencebased knowledge, can inform policymakers and other stakeholders, ultimately supporting decision-making for a sustainable future and benefiting both society and the economy. This deliverable is a preliminary report on the work that will be further developed in D3.1 Regionalised Indicators and D3.2 Extreme Indicators. This deliverable paves the way for D3.1 and D3.2. It also builds on the already achieved milestones MS5 Identification of extreme indicators for Task 3.2 and MS6 Agreement of boundaries for a set of regionalisation approaches for a choice of ocean indicators for Task 3.1. 6. References Capotondi, A., Rodrigues, R.R., Sen Gupta, A., Benthuysen, J.A., Deser, C., Frölicher, T.L., Lovenduski, N.S., Amaya, D.J., Le Grix, N., Xu, T. and Hermes, J., 2024. A global overview of marine heatwaves in a changing climate. Communications Earth & Environment, 5(1), p.701. https://doi.org/10.1038/s43247-024-01806-9 Chripko, S., R. Msadek, E. Sanchez-Gomez, L. Terray, L. Bessières, and M. Moine, 2021: Impact of Reduced Arctic Sea Ice on Northern Hemisphere Climate and Weather in Autumn and Winter. J. Climate, 34, 5847–5867, https://doi.org/10.1175/JCLI-D-20-0515.1. D 3.4 Leveraging the need of indicators: An Outline Report 33 Edwards, M., Hélaouët, P., Goberville, E. et al. North Atlantic warming over six decades drives decreases in krill abundance with no associated range shift. Commun Biol 4, 644 (2021). https://doi.org/10.1038/s42003-021-02159-1 Farchadi, N., McDonnell, L.H., Ryan, S., Lewison, R.L. and Braun, C.D., 2025. Marine heatwaves are in the eye of the beholder. Nature Climate Change, pp.1-4. https://doi.org/10.1038/s41558-025-02257-6 Hobday, A.J., Alexander, L.V., Perkins, S.E., Smale, D.A., Straub, S.C., Oliver, E.C., Benthuysen, J.A., Burrows, M.T., Donat, M.G., Feng, M. and Holbrook, N.J., 2016. A hierarchical approach to defining marine heatwaves. Progress in oceanography, 141, pp.227-238. https://doi.org/10.1016/j.pocean.2015.12.014 Ingvaldsen, R.B., Assmann, K.M., Primicerio, R. et al. Physical manifestations and ecological implications of Arctic Atlantification. Nat Rev Earth Environ 2, 874–889 (2021). https://doi.org/10.1038/s43017-021-00228-x Meccia V.L., Simolo, C., Bellomo, K., and Corti,S., 2024. 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Clark, Audrey M. Darnaude, Claire Davies, Pia Englyst, Agneta Fransson, Samantha Hallam, Emma Heslop, Elisabeth Holland, Maria Hood, Stefan Kern, Aurélien Liné, Ana D 3.4 Leveraging the need of indicators: An Outline Report 34 Lara-Lopez, Nora Loose, Belén Martín Míguez, Clive R. McMahon, Lina Mtwana Nordlund, Joanna Post, Sabrina Speich, Adrienne Sutton, Toste Tanhua, Maciej Telszewski, Dimitris Poursanidis, Weidong Yu, Global ocean indicators: Marking pathways at the sciencepolicy nexus, Marine Policy, Volume 184, 2026, 106922, ISSN 0308-597X, https://doi.org/10.1016/j.marpol.2025.106922