Emergent Constraints on Future Expansion of the Indo‐Pacific Warm Pool

• Published in: Geophysical research letters Vol. 49; no. 1
• Main Authors: Park, In‐Hong, Yeh, Sang‐Wook, Min, Seung‐Ki, Son, Seok‐Woo
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.01.2022
• Subjects: Climate; Climate change; Climate models; Convection; Correlation; Distribution; emergent relationship; Evaporation; future projection; Gases; Global precipitation; Greenhouse gases; Indo‐Pacific Warm Pool; Ocean models; Oceans; Radiation; Rain; Rainfall; Rainfall distribution; Sea surface; Sea surface temperature; Short wave radiation; Simulation; Skewed distributions; Surface temperature; Tropical climate; Tropical climates; Uncertainty; Pacific Ocean
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL097343

The latest climate models realistically simulate the present‐day climate Indo‐Pacific Warm Pool (IPWP) area, but there is considerable inter‐model spread in future projections. Here we show a strong negative relationship between the present‐day of IPWP area and its future change. When using this “emergent relationship” to constrain future IPWP area change, inter‐model spread of future projections is reduced by more than half compared to raw projections. This emergent constraint is found to be due to the negatively skewed distribution of sea surface temperature (SST) over the Indo‐Pacific Ocean as well as a negative SST‐shortwave radiation feedback in the western Pacific, which leads to a large IPWP expansion in climate models having a small IPWP area in the present‐day climate. This result indicates that a more accurate simulation of the IPWP area in the present‐day climate is crucial to reliable future projections of the tropical climate. Plain Language Summary The Indo‐Pacific Warm Pool (IPWP) is a key driver of global rainfall distribution due to its vast evaporation, deep convection, and large precipitation. Increasing of human‐induced greenhouse‐gases contributed to the observed IPWP expansion, but there is a great uncertainty in its future projections. Here, we identify multi‐model means of the latest climate models simulate the realistic IPWP in the present‐day climate and a strong negative correlation between the IPWP area in the present‐day climate and its future changes, which is an “emergent relationship.” Based on this relationship, we constrain the uncertainty of future IPWP changes by more than half the raw projections. This negative correlation is due to a negatively skewed distribution of the Indo‐Pacific Ocean sea surface temperature, leading the large IPWP expansion in climate models simulating a small IPWP in the present‐day. Thus, an improved performance of the model simulation for the IPWP in the present‐day climate is important for its reliable future projections. Key Points The Coupled Model Intercomparison Project Phase 6 (CMIP6) models reproduce the observed IPWP area with a large inter‐model difference, causing a great uncertainty in future projections The negative correlation between the present‐day state and a future change provides an emergent constraint to reduce the projection uncertainty The negatively skewed distribution of the tropical SST leads to a different increasing rates of warm pool area to global warming