The Paris Agreement set a goal to keep global warming well below 2 °C and pursue efforts to limit it to 1.5 °C. Understanding how 0.5 °C less warming reduces impacts and risks is key for climate policies. Here, we show that both areal and population exposures to dangerous extreme precipitation events (e.g., once in 10- and 20-year events) would increase consistently with warming in the populous global land monsoon regions based on Coupled Model Intercomparison Project Phase 5 multimodel projections. The 0.5 °C less warming would reduce areal and population exposures to once-in-20-year extreme precipitation events by 25% (18–41%) and 36% (22–46%), respectively. The avoided impacts are more remarkable for more intense extremes. Among the monsoon subregions, South Africa is the most impacted, followed by South Asia and East Asia. Our results improve the understanding of future vulnerability to, and risk of, climate extremes, which is paramount for mitigation and adaptation activities for the global monsoon region where nearly two-thirds of the world’s population lives.

Extreme high‐temperature events have large socioeconomic and human health impacts. East Asia (EA) is a populous region, and it is crucial to assess the changes in extreme high‐temperature events in this region under different climate change scenarios. The Community Earth System Model low‐warming experiment data were applied to investigate the changes in the mean and extreme high temperatures in EA under 1.5°C and 2°C warming conditions above preindustrial levels. The results show that the magnitude of warming in EA is approximately 0.2°C higher than the global mean. Most populous subregions, including eastern China, the Korean Peninsula, and Japan, will see more intense, more frequent, and longer‐lasting extreme temperature events under 1.5°C and 2°C warming. The 0.5°C lower warming will help avoid 35%–46% of the increases in extreme high‐temperature events in terms of intensity, frequency, and duration in EA with maximal avoidance values (37%–49%) occurring in Mongolia. Thus, it is beneficial for EA to limit the warming target to 1.5°C rather than 2°C.

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Abstract. The Global Monsoons Model Inter-comparison Project (GMMIP) has been endorsed by the panel of Coupled Model Inter-comparison Project (CMIP) as one of the participating model inter-comparison projects (MIPs) in the sixth phase of CMIP (CMIP6). The focus of GMMIP is on monsoon climatology, variability, prediction and projection, which is relevant to four of the "Grand Challenges" proposed by the World Climate Research Programme. At present, 21 international modeling groups are committed to joining GMMIP. This overview paper introduces the motivation behind GMMIP and the scientific questions it intends to answer. Three tiers of experiments, of decreasing priority, are designed to examine (a) model skill in simulating the climatology and interannual-to-multidecadal variability of global monsoons forced by the sea surface temperature during historical climate period; (b) the roles of the Interdecadal Pacific Oscillation and Atlantic Multidecadal Oscillation in driving variations of the global and regional monsoons; and (c) the effects of large orographic terrain on the establishment of the monsoons. The outputs of the CMIP6 Diagnostic, Evaluation and Characterization of Klima experiments (DECK), "historical" simulation and endorsed MIPs will also be used in the diagnostic analysis of GMMIP to give a comprehensive understanding of the roles played by different external forcings, potential improvements in the simulation of monsoon rainfall at high resolution and reproducibility at decadal timescales. The implementation of GMMIP will improve our understanding of the fundamental physics of changes in the global and regional monsoons over the past 140 years and ultimately benefit monsoons prediction and projection in the current century.

Subtropical anticyclones dominate the subtropical ocean basins in summer. Using the multimodel output from phase 5 of the Coupled Model Intercomparison Project (CMIP5), the future changes of the subtropical anticyclones as a response to global warming are investigated, based on the changes in subsidence, low-level divergence, and rotational wind. The subtropical anticyclones over the North Pacific, South Atlantic, and south Indian Ocean are projected to become weaker, whereas the North Atlantic subtropical anticyclone (NASA) intensifies, and the South Pacific subtropical anticyclone (SPSA) shows uncertainty but is likely to intensify. Diagnostic analyses and idealized simulations suggest that the projected changes in the subtropical anticyclones are well explained by the combined effect of increased tropospheric static stability and changes in diabatic heating. Increased static stability acts to reduce the intensity of all the subtropical anticyclones, through the positive mean advection of stratification change (MASC) over the subsidence regions of the subtropical anticyclones. The pattern of change in diabatic heating is dominated by latent heating associated with changes in precipitation, which is enhanced over the western North Pacific under the “richest get richer” mechanism but is reduced over subtropical North Atlantic and South Pacific due to a local minimum of SST warming amplitude. The change in the diabatic heating pattern substantially enhances the subtropical anticyclones over the North Atlantic and South Pacific but weakens the North Pacific subtropical anticyclone.

A flexible regional ocean–atmosphere–land system coupled model [Flexible Regional Ocean Atmosphere Land System (FROALS)] was developed through the Ocean Atmosphere Sea Ice Soil, version 3 (OASIS3), coupler to improve the simulation of the interannual variability of the western North Pacific summer monsoon (WNPSM). The regionally coupled model consists of a regional atmospheric model, the Regional Climate Model, version 3 (RegCM3), and a global climate ocean model, the National Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG)/Institute of Atmospheric Physics (IAP) Climate Ocean Model (LICOM). The impacts of local air–sea interaction on the simulation of the interannual variability of the WNPSM are investigated through regionally ocean–atmosphere coupled and uncoupled simulations, with a focus on El Niño’s decaying summer. Compared with the uncoupled simulation, the regionally coupled simulation exhibits improvements in both the climatology and the interannual variability of rainfall over the WNP. In El Niño’s decaying summer, the WNP is dominated by an anomalous anticyclone, less rainfall, and enhanced subsidence, which lead to increases in the downward shortwave radiation flux, thereby warming sea surface temperature (SST) anomalies. Thus, the ocean appears as a slave to atmospheric forcing. In the uncoupled simulation, however, the atmosphere is a slave to oceanic SST forcing, with the warm SST anomalies located east of the Philippines unrealistically producing excessive rainfall. In the regionally coupled run, the unrealistic positive rainfall anomalies and the associated atmospheric circulations east of the Philippines are significantly improved, highlighting the importance of air–sea coupling in the simulation of the interannual variability of the WNPSM. One limitation of the model is that the anomalous anticyclone over the WNP is weaker than the observations in both the regionally coupled and the uncoupled simulations. This results from the weaker simulated climatological summer rainfall intensity over the monsoon trough.

Previous studies on the predictability of East Asian summer monsoon circulation based on SST-constrained Atmospheric Model Intercomparison Project (AMIP)-type simulations show that this phenomenon is reproduced with lower skill than other monsoon patterns. The authors examine the reason in terms of the predictability of land-sea thermal contrast change. In the observation, a stronger monsoon circulation is dominated by a tropospheric warming over East Asian continent and a cooling over the tropical western Pacific and North Pacific, indicating an enhancement of the summertime ''warmer land-colder ocean'' mean state. The tropospheric cooling over the tropical western Pacific and North Pacific, and the tropospheric warming over East Asian continent are reproducible in AMIP-type simulations, although there are biases over both the North Pacific and East Asia. The tropospheric temperature responses in the model indicate a reasonable predictability of the meridional land-sea thermal contrast; the zonal land-sea thermal contrast change is also predictable but shows bias over the region north to 258N in North Pacific. The reproducibility of the meridional thermal contrast is higher than that of the zonal thermal contrast. An examination of the predictability of two commonly used monsoon indices reveals far different skills. The index defined as zonal wind shear between 850 and 200 hPa averaged over East Asia is highly predictable. The skill comes from the predictability of the meridional land-sea thermal contrast. Although the zonal thermal contrast change is mostly predictable except for the biases over the North Pacific, the monsoon index defined as zonal sea level pressure (SLP) difference across the East Asian continent and the North Pacific is unpredictable. The low skill is related to the index definition, which attaches more importance to the land SLP change. The limitation of the index in measuring the land SLP change reduces the model skill. Although regional features of monsoon precipitation changes remain a challenge for current climate models, the predictable land-sea thermal contrast change sheds light on monsoon circulation prediction.

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