Future climate change in the Caspian Sea and Black Sea simulated by a mesoscale-resolving Global Climate Model

Abstract:

The Caspian Sea and Black Sea are the two largest inland seas on our planet. How their circulation, freshwater balance and temperature will respond to future climate change remains unresolved. Previous studies have mostly relied on coarse resolution or on uncoupled regional climate models, with limited abilities to resolve regional circulation, topographic and thermodynamic features. Here, we present results from a series of century-long greenhouse warming simulations conducted with a mesoscale resolving version of the Community Earth System Model with a global horizontal resolution of 1/10° in the ocean and inland seas and 1/4° in the atmosphere. In response to atmospheric CO₂ doubling and quadrupling the model simulates a seasonally modulated warming attaining maximum values of 3^oC and 5^oC in the northern Caspian Sea, respectively. The Black Sea experiences a more homogenous warming and a wind stress-driven 20-35% slowdown of the main gyre circulation. Due to the warming-induced enhancement of evaporation, which is further exacerbated by the large-scale expansion of the subtropics, a negative water balance occurs over the Caspian Sea and the Black Sea basins. The freshwater deficit translates to persistent negative trends of equivalent sea level of about -0.1 cm/year to -0.25 cm/year for the two CO₂ perturbation experiments. The robust trends in temperature and sea level are likely to impact fisheries and threaten existing coastal infrastructures.