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Climate models

Photo: Lars-Johan Naustvoll

In addition to natural climate variability there is a contribution from global warming related to greenhouse gas emissions. A timely question is how this will affect the seas in our region.

We know that the physical ocean conditions are of importance for the marine ecosystems and thereby also fishery resources. The natural variability is large, and on short time scales (less than 15 years) this is more important than the slower global warming. However, on longer times scales (more than 30 years), global warming will in general dominate natural variability.

The global climate models are large and complex models that include atmosphere, ocean and sea ice, and long simulations demand large amounts of computing resources. Even with increasing computing power, these models have poor horizontal resolution in our regions. These models are relatively good in the large open basins, but less accurate in offshore seas such as the North Sea and the Barents Sea. Furthermore, the global models often have issues with sea ice processes. This is of particular importance in the Barents Sea which is the area in the Arctic with the greatest variability in the sea ice distribution. 

A way to improve this is by downscaling, where we run our regional ocean model with forcing from one or more global climate models. Among other things, we have done such downscalings for various emission scenarios in an area that covers the North Atlantic, the Nordic Seas, the Barents Sea, and the Arctic. The figure shows the trend in March sea surface temperature in the SSP5-8.5 scenario from 2015 to 2100. This scenario gives a warming of more than 4oC along the Polar Front and in the eastern part of the Barents Sea, in the Greenland Sea and north of Iceland and Svalbard, and even a cooling east of Iceland. The animation shows temperature anomalies relative the mean value for the same period and the same scenario. The large year-to-year variability illustrates the natural variability on top of the trend shown in the figure. Though, it has to be taken into consideration that the uncertainty is great, and that the results vary both between the different global models and the different scenarios.

The Institute of Marine Research's regional ocean model NEMO-NA10KM (Hordoir et al., 2021; Vihtakari et al., 2021) is used for downscaling global climate models to improve the results for our ocean areas. NEMO-NAA10KM covers the area from the North Atlantic to the Arctic, with a horizontal resolution of around 10 km in the Norwegian ocean regions. It is based on the ocean model NEMO3.6 (Madec et al., 2015) and the ice model LIM3 (Vancoppenolle et al., 2008), and simulates current, salinity, temperature, water level and sea-ice concentration and depth both backward and forward in time. Simulations that cover periods back in time, so-called hindcast simulations, are driven by observation-based atmospheric forcing fields at the sea surface and oceanographic boundary conditions of the model area. In this way, we can evaluate the model's properties such as current, hydrography and sea ice against observations. When this is done, the model can be used for regional projections by downscaling scenarios from global models. The global models have often participated in climate model intercomparison projects (CMIP) that use the same range of historical experiments and emission scenarios to easily compare the different model results. Researchers at the Institute of Marine Research have so far used NEMO-NAA10KM to scale down the Norwegian climate model NorESM2-MM (Bentsen et al., 2013) for the CMIP6 scenarios SSP1-2.6, SSP2-4.5 and SSP5-8.6 which represent low, medium and large climate challenges. The results from these simulations can then be used in the Institute of Marine Research's ecosystem models NORWECOM.e2e (Skogen et al., 2014) and NoBa Atlantis (Hansen et al., 2019a) to study the effects of climate change at different trophic levels in the marine ecosystem.

Previously, the ocean model ROMS has been used to downscale various CMIP3 and CMIP5 models (Shchepetkin and McWilliams, 2005; Sandø et al. 2014) with subsequent analyzes of effects on the marine ecosystem (Skogen et al., 2018; Hansen et al., 2019b; Sandø et al., 2020; Sandø et al., 2021).

Modellert temperatur i overflaten
Simulated sea surface temperature from NEMO-NAA10KM SSP2-4.5, average present climate (2015-2035), and future change (2080-2099 - 2015-2035). 

Hansen, C., Drinkwater, K. F., Jähkel, A., Fulton, E. A., Gorton, R., and Skern-Mauritzen, M. 2019a. Sensitivity of the norwegian and barents sea atlantis end-to-end ecosystem model to parameter perturbations of key species. PLOS ONE, 14: 1–24. URL https://doi.org/10.1371/journal.pone.0210419.
Hansen, C., Nash, R. D. M., Drinkwater, K. F., and Hjøllo, S. S. 2019b. Management scenarios under climate change – a study of the Nordic and Barents Seas. Frontiers in Marine Science, 6: 668. URL https://www.frontiersin.org/article/10.3389/fmars.2019.00668.
Hordoir, R., Ingvaldsen, R., Skagseth, Ø., Sandø, A. B., Loptien, U., Dietze, H., and Lind, S.Changes in Arctic Stratification and Mixed Layer Depth Cycle, A Modeling Analysis. Submitted to JGR Ocean.
Sandø, A. B., Budgell, W. P., Ådlandsvik, B., Skogen, M. D., Hjøllo, S. S., and Mousing, E. A. 2021. Barents Sea plankton production and controlling factors in a fluctuating climate. Conditionally accepted in ICES J. Mar. Sci.
Sandø, A. B., Johansen, G. O., Aglen, A., Stiansen, J. E., and Renner, A. H. H. 2020.
Climate change and new potential spawning sites for Northeast Arctic cod. Frontiers in Marine Science, 7: 28. URL https://www.frontiersin.org/article/10.3389/fmars.2020.00028.
Sandø, A. B., Melsom, A., and Budgell, W. P. 2014. Downscaling IPCC control run and future scenario with focus on the Barents Sea. Ocean Dynamics, 64: 927–949.
Shchepetkin, A. F. and McWilliams, J. C. 2005. The regional oceanic modeling system (ROMS): a split-explicit, free-surface, topography-following-coordinate oceanic model. Ocean Modelling, 9: 347–404.
Skogen, M. D., Hjøllo, S. S., Sandø, A. B., and Tjiputra, J. 2018. Future ecosystem changes in the Northeast Atlantic: a comparison between a global and a regional model system. ICES Journal of Marine Science, p. fsy088. URL http://dx.doi.org/10.1093/icesjms/fsy088.
Skogen, M. D., Olsen, A., Børsheim, K. Y., Sandø, A. B., and Skjelvan, I. 2014. Modelling ocean acidification in the nordic and barents seas in present and future climate. Journal of Marine Systems, 131: 10 – 20.
Vihtakari, M., Robinson Holdoir, Margaret Treble, Meaghan D. Bryan, Bjarki Elvarsson, Adriana Nogueira, Elvar H. Hallfredsson, Jørgen Schou Christiansen, and Ole Thomas Albert. Pan-Arctic suitable habitat model for Greenland halibut. ICES Journal of Marine Science (2021), doi:10.1093/icesjms/fsab007 (In Press)