Wu et al. (2025) Perspective on the shifting interannual variability of recent summer temperature modes in eastern China: Roles of Arctic sea-ice, Arctic Oscillation and Pakistan precipitation

Identification

• Journal: npj Climate and Atmospheric Science
• Year: 2025
• Date: 2025-11-07
• Authors: Zeming Wu, Chundi Hu, Kuo Wang, Renguang Wu, Lin Lifei, Dake Chen
• DOI: 10.1038/s41612-025-01236-0

Research Groups

• State Key Laboratory of Ocean Sensing & Ocean College, Zhejiang University, Zhoushan, China
• School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, China
• Zhejiang Climate Center, Zhejiang Meteorological Bureau, Hangzhou, China
• Nagchu Meteorological Bureau, Nagchu, China
• School of Earth Sciences, Zhejiang University, Hangzhou, China
• State Key Laboratory of Satellite Ocean Environment Dynamics (SOED), Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China

Short Summary

This study reveals a fundamental reorganization of interannual summer temperature variability in eastern China, characterized by an enhancing south-north uniform warming (SNUW) mode and a disappearing south-north meridional dipole (SNMD) mode. These shifts are driven by increasing Pakistan convective precipitation and Arctic Oscillation variability for SNUW, and reduced Barents-Kara sea-ice variability for SNMD, with implications for future extreme heat events.

Objective

• To investigate the recent changes in high-summer (July–August) interannual temperature variability in eastern China, focusing on the south-north uniform warming (SNUW) mode and the south-north meridional dipole (SNMD) mode.
• To clarify the physical mechanisms driving these changes, distinguishing between natural variability and anthropogenic warming.
• To explore the potential future evolution of these interannual temperature variability modes under global warming using climate model projections.

Study Configuration

• Spatial Scale: Eastern China (22°–38°N, 105°–123°E for EOF analysis region), Yangtze River, Barents-Kara seas (74°–85°N, 20°–90°E for SIC index), Pakistan (18°–30°N, 60°–76°E for PCP index), Arctic (for AO).
• Temporal Scale: High-summer (July–August); observational period: 1984–2023, divided into sub-periods 1984–2003 (P1) and 2004–2023 (P2); CMIP6 model projections: 1850–2100 (historical and SSP585 experiments).

Methodology and Data

• Models used: Coupled Model Intercomparison Project Phase 6 (CMIP6) multi-model ensemble (MME), comprising 29 models.
• Data sources:
  • Reanalysis: European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis version 5 (ERA5; 0.25° × 0.25° resolution, interpolated to 1° × 1° for T2m and 2.5° × 2.5° for other fields), ECMWF Reanalysis of the Twentieth Century (ERA-20C), NCEP/NCAR Reanalysis 1.
  • Sea-ice concentration: Centennial in situ Observation-Based Estimates of the Variability of SST and Marine Meteorological Variables, version 2 (COBE2; 1° × 1° resolution).
  • Precipitation: Global Precipitation Climatology Project (GPCP) version 2.3 (2.5° × 2.5° resolution), Global Precipitation Climatology Centre (GPCC) version 2022 (1° × 1° resolution), CPC Merged Analysis of Precipitation (CMAP) enhanced version (2.5° × 2.5° resolution), NOAA precipitation reconstruction over land (PREC/L; 0.5° × 0.5° resolution).
  • Methods: Empirical Orthogonal Function (EOF) analysis, Pearson correlation, linear regression, Student’s t-test, Bayley and Hammersley’s method for effective degrees of freedom, wave activity flux (WAF).

Main Results

• A significant reversal in the interannual variability of eastern China's dominant summer temperature modes occurred around 2004.
• The South-North Uniform Warming (SNUW) mode's variability has strengthened, becoming dominant after 2004, with its explained variance increasing from 29.4% (1984–2003) to 44.7% (2004–2023).
• The South-North Meridional Dipole (SNMD) mode's variability has significantly weakened and largely disappeared after 2004, with its explained variance dropping from 39.3% to 18.9%.
• The strengthening SNUW variability is primarily associated with increasing interannual variability of Pakistan convective precipitation (PCP) and Arctic Oscillation (AO). PCP variability is linked to anthropogenic warming, while AO variability reflects natural fluctuations.
• The decline in SNMD variability is attributed to a ~60% reduction in interannual sea-ice variability in the Barents-Kara seas after 2004, which led to the disappearance of a propagating Rossby wavetrain towards eastern China.
• CMIP6 model projections indicate that future SNUW amplification will be dominated by increasing PCP variability, with the AO's influence likely limited to internal cyclical fluctuations.
• CMIP6 models consistently project a further disappearance of the SNMD mode in the future due to an increase in regional temperature uniformity.
• Quantitative attribution for SNUW variability (1984–2023): Approximately 38 ± 29% of the increase is attributable to external anthropogenic forcing, and 62 ± 29% to internal variability.

Contributions

• Reveals a fundamental reorganization of interannual temperature variability in eastern China under climate warming, providing a new perspective on recent rapid changes in regional temperature variability.
• Offers a mechanistic explanation for the observed shifts in SNUW and SNMD modes, distinguishing the roles of natural internal variability (Arctic Oscillation, Barents-Kara sea-ice) and anthropogenic warming (Pakistan convective precipitation).
• Emphasizes the critical role of changes in temperature variability, beyond just mean temperature increases, in shaping the dynamics and increasing frequency of extreme heat events (EHEs).
• Highlights that escalating Pakistan convective precipitation variability is projected to dominate future SNUW amplification, implying more prominent EHEs in eastern China.

Funding

• National Key Research and Development Program of China (2022YFE0106800)
• National Natural Science Foundation of China (41975077)
• Zhejiang University “Ocean College Seed Fund”: Excellent Young Teachers Training Project (2025YQ001)
• Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai) (No. 311024001)
• Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies (Grant 2023B1212060019)
• National Program on Global Change and Air-Sea Interaction (GASI-IPOVAI-04)
• Zhuhai Joint Innovative Center for Climate, Environment and Ecosystem
• Open fund of State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources (No. QNHX2331)
• Research start-up funding support of the “Top 100 Talents Plan” Project of Zhejiang University

Citation

@article{Wu2025Perspective,
  author = {Wu, Zeming and Hu, Chundi and Wang, Kuo and Wu, Renguang and Lifei, Lin and Chen, Dake},
  title = {Perspective on the shifting interannual variability of recent summer temperature modes in eastern China: Roles of Arctic sea-ice, Arctic Oscillation and Pakistan precipitation},
  journal = {npj Climate and Atmospheric Science},
  year = {2025},
  doi = {10.1038/s41612-025-01236-0},
  url = {https://doi.org/10.1038/s41612-025-01236-0}
}