The long-term trend of Bohai Sea ice in different emission scenarios

Abstract

Based on a coupled ocean-sea ice model, this study investigates how changes in the mean state of the atmosphere in different CO2 emission scenarios (RCP 8.5, 6.0, 4.5 and 2.6) may affect the sea ice in the Bohai Sea, China, especially in the Liaodong Bay, the largest bay in the Bohai Sea. In the RCP 8.5 scenario, an abrupt change of the atmospheric state happens around 2070. Due to the abrupt change, wintertime sea ice of the Liaodong Bay can be divided into 3 periods: a mild decreasing period (2021–2060), in which the sea ice severity weakens at a near-constant rate; a rapid decreasing period (2061–2080), in which the sea ice severity drops dramatically; and a stabilized period (2081–2100). During 2021–2060, the dates of first ice are approximately unchanged, suggesting that the onset of sea ice is probably determined by a cold-air event and is not sensitive to the mean state of the atmosphere. The mean and maximum sea ice thickness in the Liaodong Bay is relatively stable before 2060, and then drops rapidly in the following decade. Different from the RCP 8.5 scenario, atmospheric state changes smoothly in the RCP 6.0, 4.5 and 2.6 scenarios. In the RCP 6.0 scenario, the sea ice severity in the Bohai Sea weakens with time to the end of the twenty-first century. In the RCP 4.5 scenario, the sea ice severity weakens with time until reaching a stable state around the 2070s. In the RCP 2.6 scenario, the sea ice severity weakens until the 2040s, stabilizes from then, and starts intensifying after the 2080s. The sea ice condition in the other bays of the Bohai Sea is also discussed under the four CO2 emissions scenarios. Among atmospheric factors, air temperature is the leading one for the decline of the sea ice extent. Specific humidity also plays an important role in the four scenarios. The surface downward shortwave/longwave radiation and meridional wind only matter in certain scenarios, while effects from the zonal wind and precipitation are negligible.