Editing IPCC:AR6/WGI/Chapter-8 (section)

===== 8.4.2.4.2 East Asian Monsoon =====

<div id="h4-20-siblings" class="h4-siblings"></div>

In AR5, the East Asian monsoon (EAsiaM) was projected to intensify in terms of precipitation, with an earlier onset and longer duration of the summer season. Since AR5, there has been improved understanding of future projected changes in the EAsiaM.

CMIP5 projections indicated a possible intensification of the EAsiaM circulation during the 21st century, in addition to precipitation increase, although there is a lack of consensus on changes in the western North Pacific subtropical high, this is an important feature of the EAsiaM circulation ( [[#Kitoh--2017|Kitoh, 2017]] ). Furthermore, the EAsiaM precipitation enhancements in the CMIP5 projections are prominent over the southern part of the Baiu rainband by the late 21st century, with no significant changes in the Meiyu precipitation over central-eastern China ( [[#Horinouchi--2019|Horinouchi et al., 2019]] ). It was also shown that the Baiu precipitation response in CMIP5 projections is accompanied by a southward retreat of the western North Pacific subtropical high and a southward shift of the East Asian subtropical jet ( [[#Horinouchi--2019|Horinouchi et al., 2019]] ). According to the high-resolution MRI-AGCM global warming experiments, future summer precipitation could potentially increase on the southern side and decrease on the northern side of the present-day Baiu location in response to downward-motion tendencies which can offset the ‘wet-gets-wetter’ effect, but is subject to large model uncertainties ( [[#Ose--2019|Ose, 2019]] ). Future projections of land warming over the Eurasian continent ( [[#Endo--2018|Endo et al., 2018]] ) and intensified land – sea thermal contrast (Z. [[#Wang--2016|]] [[#Wang--2016|]] [[#Wang--2016|Wang et al., 2016]] ; [[#Tian--2019|Tian et al., 2019]] ) can potentially intensify the EAsiaM circulation during the 21st century. However, there are large uncertainties in projected water cycle changes over the region ( [[#Endo--2018|Endo et al., 2018]] ), mostly in the near-term because of uncertainties in future aerosol emissions scenarios ( [[#Wilcox--2020|Wilcox et al., 2020]] ), as well as due to the interplay between internal variability and anthropogenic external forcing ( [[#Wang--2021|Wang et al., 2021]] ).

Inter-hemispheric mass exchange can act as a bridge connecting SH circulation with EAsiaM rainfall, however this inter-hemispheric link is projected to weaken in a future warmer climate as seen from a CCSM4 projection using the RCP8.5 scenario ( [[#Yu--2018|Yu et al., 2018]] ). A comparison of 1.5°C and 2°C global warming levels reveals how a 0.5°C difference could result in precipitation enhancement over large areas of East Asia ( D. Lee et al. , 2018; J. Liu et al. , 2018; Chen et al. , 2019 ), with substantial increases in the frequency and intensity of extremes ( [[#Chevuturi--2018|Chevuturi et al., 2018]] ; D. [[#Li--2019|]] [[#Li--2019|Li et al., 2019]] ). Future monsoon projections from the CMIP6 models show increase of EAsiaM precipitation across all the scenarios (Z. [[#Chen--2020|]] [[#Chen--2020|Chen et al., 2020]] b), though with a large model spread mostly on the long-term and in the higher emissions scenarios (Figure 8.22). Considering all the five scenarios used across the report, changes in precipitation, runoff and P–E over the EAsiaM are positive and become larger for highest emissions scenarios and for the long-term mean, except for the mid-term SSP1-1.9 scenario where the changes are close to zero or even negative (Table 8.2). Additionally, CMIP6 models confirm a projected increased length of the EAsiaM season due to early onset and late retreat ( [[#Ha--2020|Ha et al., 2020]] ).

In summary, despite the uncertainties in the monsoon circulation response in CMIP5 and CMIP6 models, there is ''high confidence'' that summer monsoon precipitation over East Asia will increase in the 21st century and ''medium confidence'' that the monsoon season will be longer.

<div id="8.4.2.4.3" class="h4-container"></div>

<span id="west-african-monsoon-1"></span>