Projecting the Impact of Climate Change on the Black Sea: A High-Resolution Regional Modeling Study

Global climate models struggle to accurately represent the dynamics of the Black Sea because it's so isolated from the open ocean, connected only by the narrow Turkish Straits. To overcome this limitation and study how the Black Sea will be affected by future climate change, we need to use high-resolution regional models. We've developed a new 5km resolution regional model of the Black Sea using the NEMO 4.2.1 ocean circulation model. To validate our new model, we compared it against a well-established 2.5-km resolution model from the Copernicus Marine Service model setup. Both models share the same numerical core, vertical layers, horizontal and vertical parameterizations.

 

In our first comparison, we used historical ERA5 atmospheric data from 1980 to 2015. The new 5km model performed very well, with biases that were remarkably similar to those of the higher-resolution 2.5-km model. While the 2.5-km model revealed finer details like the Batumi Gyre and specific features near the Crimea Peninsula, both models provided comparable results for deep-ocean dynamics. This confirms that our 5-km model is reliable enough for long-term climate simulations.

Next, we simulated three different future climate scenarios—RCP2.6, RCP4.5, and RCP8.5—using atmospheric data from the 0.01 degree CNRM-ALADIN model in the CMIP5 CORDEX-Europe project. All three scenarios show that the Black Sea surface will get warmer and saltier. In the model simulations, the surface temperature increases 1.5, 2.0, 3.5 degrees between different RCP scenarios respectively, and also gets saltier up to 3 psu. Notably, the Cold Intermediate Layer (CIL), a distinct oceanographic feature which is characterized by a layer of relatively cold water is projected to disappear after 2040 in the RCP8.5 scenario. The warming isn't limited to the surface; it penetrates deep, reaching down to 700 meters. Likewise, the Black Sea is becoming saltier, with this salinification also extending to 700 meters. To increase the robustness of our findings, we also performed an additional RCP8.5 simulation using a different atmospheric model, the SMHI-RCA4 from the CMIP5 CORDEX-Europe project. This ensemble approach helps us account for model uncertainties and strengthens our confidence in the projected climate changes for the Black Sea.

These findings suggest that under a high-emission scenario like RCP8.5, the Black Sea's temperature and salinity profiles will change dramatically. These changes could significantly alter its circulation patterns, stratification, and overall ecosystem dynamics.