海洋环流的长期变化和预估

IPCC第六次评估报告(AR6)于2021年8月在IPCC第一工作组第14次联合大会上得到审议通过,并得到了IPCC第54届全会接受和批准.文中主要对该报告第九章"海洋、冰冻圈和海平面"中与海洋环流的相关评估内容进行解读.与以前的IPCC报告相比,AR6进一步确认人类活动对海洋环流的影响,并基于最新的数值模式给出对未来...

Long term variation and projection of ocean circulation

IPCC AR6 was formally approved at the 14th joint session of Working Group I of the IPCC and accepted by the 54st session of the IPCC on August 2021. Assessment content related to the ocean circulation of chapter 9 “Ocean, cryosphere and sea level change” is synthesized in this paper. Compared to the former IPCC reports, AR6 further confirmed the influence of human activities on ocean circulation, and provided the projected results based on the newest numerical simulations. AR6 pointed out that, surface salinity contrasts are increasing (virtually certain), and fresh ocean regions will continue to get fresher and salty ocean regions will continue to get saltier in the 21st century (medium confidence). The upper ocean has stably stratified since at least 1970 over the vast majority of the globe (virtually certain), and the upper ocean stratification is projected to increase (virtually certain) while the mixed layer depth is projected to mostly shoal under high emissions scenarios (low confidence). The frequency of marine heatwaves has doubled since the 1980s (high confidence) and the duration has become longer (medium confidence), furthermore the projection shows such trend will continue. Of the four eastern boundary upwelling systems (EBUS), only the California current system has experienced upwelling-favorable wind intensification since the 1980s (medium confidence), and the EBUS will change with a dipole spatial pattern of reduction at low latitude and enhancement at high latitude (high confidence). Under all SSP scenarios, the Atlantic Meridional Overturning Circulation (AMOC) will decline over the 21st century (very likely). The decline will not involve an abrupt collapse before 2100 (medium confidence). AR6 has added the high resolution numerical simulation experiments which could resolve mesoscale eddy, such experiments could effectively improve the simulation of Sea Surface Temperature (SST), air-sea flux and dynamic sea-level change.