Hysteretic Behavior of Global to Regional Monsoon Area Under CO₂ Ramp‐Up and Ramp‐Down

Abstract

When projecting future monsoon changes by carbon dioxide (CO2) pathway, most studies have analyzed precipitation responses without considering monsoon area (total area of monsoon domain, MA) variations. However, how MA responds to CO2 removal remains uncertain. This study evaluates MA variations and impacts in idealized CO2 ramp‐up (toward CO2 quadrupling), ramp‐down, and stabilized simulations using the Community Earth System Model version 1. Global MA negatively overshoots (i.e., recovery with decreasing tendency beyond the original MA) during the ramp‐down period due to reduced or rapidly recovered MA in several regional monsoons, including Northern and Southern Africa, South and East Asia, and South America, showing hysteresis when comparing CO2 ramp‐up and ramp‐down periods despite similar global warming levels. These non‐linear regional MA variations come from distinct regional summer and winter precipitation variations, which are found to be mostly associated with Intertropical Convergence Zone movements and El Niño‐like response. Further, regional monsoon precipitation characteristics also vary through CO2 ramp‐up and ramp‐down periods consistently with overall hysteresis. Changes in total monsoon precipitation resemble the distinct responses of MA. Our results suggest that regions characterized by a monsoonal climate may experience reduced seasonal rainfall variations under net‐negative CO2 emissions.

Tipping points in ocean and atmosphere circulations

“…It will likely continue in the future (high confidence, IPCC AR6, by ~1-3% per °C warming) because of increased water vapour related to warming driven by increased CO2 in the atmosphere (Hsu et al, 2013;Lee and Wang, 2014;Chen et al, 2020;Moon and Ha, 2020;Wang et al, 2020), although a few studies conversely show that climate warming may lead to a weakened global monsoon circulation (Hsu et al, 2012(Hsu et al, , 2013. Climate simulations also project expansion of global monsoon domain areas with increasing CO2 (Wang et al, 2020;Paik et al, 2023) and increased frequency of monsoon precipitation extremes in the 21st Century (Chevuturi et al, 2018;Ali et al, 2020, Modi andMishra, 2019;Moon and Ha, 2020;Katzenberger et al, 2021).…”

Hemispheric Asymmetric Response of Tropical Cyclones to CO2 Emission Reduction

“…Nevertheless, even a rapid removal of atmospheric CO 2 will not immediately eradicate the effects of climate change due to the hysteresis phenomenon arising from the inertial and inherently long adjustment timescales of the climate system 40,42 . Using various hypothetical CO 2 removal scenarios, the hysteresis phenomenon has been found in the surface temperature 40,43 , precipitation 38,[44][45][46] , sea level 40 , the ITCZ 47 , the Hadley circulation 48 , the monsoon [49][50][51] , the Atlantic Meridional Overturning Circulation (AMOC) 43 , the El Niño-Southern Oscillation [52][53][54][55] , and many other Earth's system elements, with hysteresis timescales ranging from a few decades to centuries 39 . The pervasiveness of climate hysteresis suggests that it is imperative to take its effects into account when designing climate change mitigation and adaptation policies, and this requires a better understanding of the issues involved.…”

Monsoon Hysteresis reveals Atmospheric Memory

“…The combination of two oceanic memory effects, namely in the Atlantic overturning and in slower warming or cooling in the Southern Ocean, could yield hysteresis in the Inter-Tropical Convergence Zone ( 14). The accumulation of heat in the ocean has been shown to cause hysteresis of global mean precipitation (15) as well as the asymmetry of monsoon systems in a CO 2 ramp-up and ramp-down in numerical simulations, and El-Niño-related anomalies (16)(17)(18). So far atmospheric hysteresis has always originated from an oceanic memory effect (19).…”