Weakening Subtropical Circulation under Greenhouse Warming


The latest climate models show a weakening of the subtropical circulation in a scenario of stable greenhouse warming, according to a new study published in Nature Communications.
The low-level subtropical atmospheric circulation, encompassing monsoons over land and high-pressure zones over ocean, plays a pivotal role in shaping the climate, ecosystems, and societies of the surrounding regions.
The study, jointly conducted by researchers from the Institute of Atmospheric Physics at the Chinese Academy of Sciences and Yunnan University explored various future carbon emission scenarios, uncovering two key drivers behind the changes in subtropical circulation: the land–sea thermal contrast due to direct effect of CO2 and surface warming. These two factors work on distinct time scales.
This means the thermal contrast strengthens the circulation most significantly in the beginning, whereas the diminishing effect caused by surface warming unfolds gradually.
Professor HUANG Ping, the corresponding author of the study, explains, "The varying contributions of these two factors across different scenarios lead to diverse outcomes in the model projections. However, in a more stable warming scenario, the subtropical circulation is expected to weaken significantly."

The study utilizes cutting-edge climate models to assess changes in the intensity of the lower-level subtropical atmospheric circulation due to greenhouse warming. The results show that the weakened subtropical circulation implies a reduced monsoon range and increased dryness at the edges of arid regions under a scenario of stable warming. Meanwhile, accurate projections of near-term changes in subtropical circulation demand a thorough consideration of greenhouse gas emission trajectories and the timescales of two key drivers.
"The finding is also helpful to understand subtropical circulation changes in specific regions, where large uncertainties persist in the current knowledge." said Dr. ZHOU Shijie, the lead author.
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