The IPCC's Sixth Assessment Report highlights that climate change is more severe than previously understood, with profound implications for marine systems. The ocean, which has historically buffered climate change, is now starting to experience significant alterations in its physical properties and biogeochemistry, including changes in sea temperature, sea level, ice coverage, current patterns, and chemical composition. These transformations are expected to push many marine species and ecosystems beyond their adaptive capacities, with potentially widespread consequences. The seas of the Nordic region are characterized by expected rapid climate development and unique marine environments, which may be especially vulnerable to climate change. Thus, for the Nordic countries understanding the impacts is crucial for preparing marine-based industries and maintaining the region's environmental leadership.
From a Nordic perspective it is particularly challenging that the state-of-the-art global climate models used to simulate future climate and climate effects under different emission scenarios (Coupled Model Intercomparison Project Phase 6, CMIP6) do not have sufficient resolution to provide a good basis for decision-making on our regional scale. The Nordic Council of Ministers (NCM) took an initiative towards diminishing the gaps between available and wanted information, thus aiming to increase our understanding of the effects of future climate change specifically on the Nordic sea areas. Through the program Marine Management and Climate and specifically the call Climate change in Nordic sea areas towards 2100, NCM has asked for regional analyses and assessments.
Our project NorScen - Nordic climate Scenarios - answers to work package 1 of this call. By producing detailed model data for future values of physical, biogeochemical, and ecological variables across the Nordic sea areas, the project has throughout strived to enhance understanding of climate change impacts, facilitate economic and societal adaptation, and provide a robust knowledge base for decision-makers.
Although well integrated, the work was carried out ocean by ocean in parallel, allowing to build upon models already set up for the area. These large models take years to develop so it’s highly important to build upon existing systems. The focus is on downscaling from global to regionally resolved information, running model simulations for both historical periods and future (IPCC) scenarios. Based on the resulting physical values, we have produced data fields on historical and future values also for biogeochemical and ecological variables. Geographically and scale-wise we cover comprehensively and on different scales, from the Danish Limfjord and the Baltic Sea via the North Sea to the Norwegian- and Barents seas. The core of the report is structured according to geographical area, as is most of this summary. The report only briefly touches upon the methods/models applied, focusing more on describing, presenting, and discussing the main results. Still, although the typical reader of this report is not a scientist with technical expertise in the field, we have chosen to retain a certain level of complexity, especially some of the figures relating to model validation and comparison are aimed at those with more in-depth interest in the topic. Nevertheless, the figure captions and main text should be helpful to everyone. For even more thorough and detailed presentation, large parts of the material presented here is recently, or will soon be, published in scientific papers, which we refer to.
SMHI applied the ocean model NEMO-SCOBI to the North Sea and Baltic Sea. Downscaled physical and biogeochemical fields were produced for the historical period 1951–2014 and future IPCC scenarios SSP1-2.6 (low emission, high mitigation) and SSP3-7.0 (high emission, low mitigation). Under the high-emission SSP3-7.0 scenario, surface temperatures are projected to increase by 2.5–3°C in the Baltic Sea and 1–2 °C in the North Sea by the end of the 21st century, with a more modest increase of around 1 °C in the Baltic Sea and less than 0.5 °C in the North Sea under the lower-emission SSP1-2.6 scenario.
Significant changes are also found for other parameters, including a general decrease in salinity, particularly in the Baltic Sea's bottom water, and a substantial reduction in ice cover. For the SSP3-7.0 scenario, ice will largely remain only in the Gulf of Bothnia and Gulf of Finland, with the central Bothnian Sea expected to be ice-free in most future years. The time evolution of sea surface temperature and salinity reveals multidecadal variability, with the long-term climate trend being more pronounced in the SSP3-7.0 scenario and markedly larger temperature increases in the Baltic Sea compared to the North Sea.
Complex changes in nutrient dynamics across the Baltic Sea and North Sea are projected, with dissolved inorganic nitrogen (DIN) and phosphorus (DIP) concentrations showing varied patterns depending on location and emission scenario. Under most conditions, nutrient loads are projected to decrease, particularly in the SSP1-2.6 low-emission scenario, with notable reductions in coastal areas. However, some regions, like the Gulf of Bothnia and along the North Sea coast of Scotland, show slight increases in nutrient concentrations, likely due to changes in riverine nutrient inputs and increased runoff.
These nutrient load changes are expected to significantly impact marine ecosystem processes, including primary production, phytoplankton concentrations, and bottom oxygen conditions. The SSP1-2.6 scenario generally projects an improvement in water quality, with reduced primary production and enhanced bottom oxygen levels. The higher-emission SSP3-7.0 scenario suggests less favourable conditions with higher runoff and increased eutrophication, though still potentially better than current conditions. Importantly and in accordance with earlier work on the Baltic Sea, we conclude that the impacts of nutrient load changes are more significant than those of climate change, with an overall expectation of future decreased eutrophication and improved water quality in the Baltic.
Aarhus University examined the future conditions in Limfjorden, northern Denmark, with the high-resolution FlexSem model set up in a 3D coupled hydrodynamic-biogeochemical model. Future development within the three climate scenarios SSP1-2.6, SSP2-4.5, and SSP5-8.5 are explored and compared with historical values for the period 2009–2018. Limfjorden is a shallow fjord stretching from the North Sea to the Kattegat, characterized by seasonal oxygen depletion, saline waters in the west and brackish in the east. This is the most important area for mussel fishing and -farming in Denmark but is negatively impacted by agricultural runoff.
All three climate scenarios project decreasing salinity and increasing water temperatures. The most significant changes are, as can be expected, in the SSP5-8.5 scenario, showing potential water temperature rises up to 5 °C and strong water column stratification for 2090–2099.
The accuracy of FlexSem for Limfjorden with regards to biogeochemical variables was rigorously validated with seasonal measurements. FlexSem quite accurately reproduces seasonal variations in nutrients, phytoplankton, and oxygen concentrations, but has some limitations in representing short-term variations. The most severe ecosystem changes are found for the SSP5-8.5 scenario and the latest time period 2090–2099. Within this scenario there is significant oxygen depletion and reduced benthic mussel biomass by 2090–2099. Also when Water Management Plans (Miljø-og-Fødevareministeriet 2016) are implemented, climate change prevents ecological improvement, with increased temperature and stratification hampering oxygen supply. The biomass of benthic mussels is reduced in all three scenarios. On the other hand, mussel farming in the water column, which is less hampered by oxygen depletion than the bottom, is expected to expand significantly in all scenarios.
IMR have studied climate scenarios for the Norwegian- and Barents Seas by downscaling with the NEMO-NAA10km model. This is a regional ocean modelling configuration designed to study ocean processes and climate impacts. Two climate models are presently used to force Nemo-NAA10km in climate downscaling mode, NorESM2 and EC-Earth. An important long-term contribution is that in NorScen we developed an enhanced method for handling river runoff in climate downscaling simulations by re-routing two-dimensional climate model runoff fields to the Nemo-NAA10km grid. Monthly runoff fields from 1950–2100 that preserve inter-annual variability while maintaining consistency with original hindcast simulation inputs were created.
Biogeochemistry is modelled with NORWECOM.E2E, a comprehensive biogeochemical model system that includes a nutrient–phytoplankton–zooplankton–detritus (NPZD) module with two types of phytoplankton and zooplankton. In this study NORWECOM.E2E was run offline using 5-day mean values from the NEMO-NAA10km physical ocean fields and NorESM2 atmospheric fields.
The new Nemo-NAA10km version with improved runoff distributions shows more moderate changes in surface salinities and sea surface temperatures compared to the old version, particularly in the Barents, Kara, and Norwegian seas, with less extreme variations and a generally shallower mixed layer depth in the subpolar region. In the main text of the report, we show example maps of future sea surface salinity and temperature and mixed layer depth from the new enhanced model runs. Also, time series and trends for projected values of these variables under different scenarios for open ocean and coastal regions in the Norwegian Sea and Barents Sea are shown, so are similar figures for net primary production (NPP) and gross secondary production (GSP). NPP is currently highest in coastal and ice-free regions, with minimal changes across emission scenarios until mid-century, after which SSP5-8.5 shows a significant increase in the Arctic part of the Barents Sea, doubling NPP by century's end. GSP follows similar trends, with a general increase across all areas, most pronounced in the Arctic part of the Barents Sea under the high-emissions SSP5-8.5 scenario.
The frequency and intensity of marine heat waves (MHWs) in Nordic waters is increasing, with the Barents Sea experiencing a 62% increase in annual MHW frequency since 2004. Further, projections by other authors suggest that the North Sea and Norwegian Sea could see 20–30 times higher MHW probability in a 3.5 °C warming scenario. Our ongoing research characterises historical MHW events, distinguishing between surface and near-bottom MHWs. We find increasing trends in frequency and intensity, with notable variations in different marine regions.
The Norwegian and Barents Seas Atlantis model (NoBa Atlantis) is a comprehensive ecosystem model with 53 species and functional groups, representing commercial species individually and smaller groups collectively. The model uses a three-dimensional grid to represent the ecosystem, with each grid cell representing a specific area of the sea. The model incorporates temperature sensitivity through a knife-shaped approach affecting movement, spawning, and growth rates, and requires daily input of physical parameters. To address uncertainty in phytoplankton and zooplankton responses to climate change, our researchers conducted nine perturbation simulations across three emission scenarios, varying growth rates based on projections from NORWECOM.E2E.
Species responses to the projected higher temperatures vary widely, mainly based on their temperature tolerance. Prawns and mesopelagic fish are climate winners, while capelin and Greenland halibut are losers. Polar cod showed, rather surprisingly, no clear response due to uncertain links between recruitment and sea ice. Seven species had positive responses, with differences becoming evident after 2065. Haddock showed strong responses due to recruitment variability. Prawns thrived in warmer shallow waters, despite some areas exceeding their tolerance. Twelve species responded negatively to higher temperatures. Contrary to earlier projections this includes Atlantic cod, declines found by our NoBa Atlantis analyses are linked to reduced prey, capelin and zooplankton, availability.
Additional funding allowed us to arrange a workshop on Economic consequences of climate change towards 2100 for fisheries and aquaculture in the Nordic region. The workshop brought together a multidisciplinary expert group of resource economists, fisheries oceanographers, and biologists, and one representative from the fishing industry. A broad range of topics were discussed and a comprehensive account included as part of this report. This is structured as follows: Expected developments, challenges and adaptation strategies for both fisheries and aquaculture under climate change, followed by a comprehensive chapter on Fisheries by ocean region, and Aquaculture. Fishery and aquaculture may have completely different development paths and issues in the future. Fisheries will likely in many areas be challenged by negative impacts of climate change. If fisheries are strongly reduced, aquaculture may be subsidised to sustain settlement along the coast, but to thrive the aquaculture industry must be flexible. Technological advancements and economic drivers are crucial for the future. Already now the industries face challenges with high costs, rising demands for sustainable practices, and competition for land and sea space. While some issues may be solved in the relatively near future (like change of fuel), others may intensify. In addition, and especially in Norway, both the fisheries and aquaculture industries must expect debates on the balance between the nation’s future role as a food producer or primarily a technology developer and supplier.