Climate Change Research ›› 2022, Vol. 18 ›› Issue (1): 19-30.doi: 10.12006/j.issn.1673-1719.2021.230

• Special Section on the Sixth Assessment Report of IPCC: WGI • Previous Articles     Next Articles

Long term variation and projection of ocean circulation

HUA Li-Juan1(), YU Yong-Qiang2,3   

  1. 1 State Key Laboratory of Severe Weather (LASW), Chinese Academy of Meteorological Sciences, Beijing 100081, China
    2 State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
    3 College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2021-10-08 Revised:2021-11-08 Online:2022-01-30 Published:2021-12-22

Abstract:

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.

Key words: Climate change, Ocean circulation, Marine heatwave, High resolution model

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