title: Human-caused Indo-Pacific warm pool expansion.
abstract: The Indo-Pacific warm pool (IPWP) has warmed and grown substantially during the past century. The IPWP is Earth's largest region of warm sea surface temperatures (SSTs), has the highest rainfall, and is fundamental to global atmospheric circulation and hydrological cycle. The region has also experienced the world's highest rates of sea-level rise in recent decades, indicating large increases in ocean heat content and leading to substantial impacts on small island states in the region. Previous studies have considered mechanisms for the basin-scale ocean warming, but not the causes of the observed IPWP expansion, where expansion in the Indian Ocean has far exceeded that in the Pacific Ocean. We identify human and natural contributions to the observed IPWP changes since the 1950s by comparing observations with climate model simulations using an optimal fingerprinting technique. Greenhouse gas forcing is found to be the dominant cause of the observed increases in IPWP intensity and size, whereas natural fluctuations associated with the Pacific Decadal Oscillation have played a smaller yet significant role. Further, we show that the shape and impact of human-induced IPWP growth could be asymmetric between the Indian and Pacific basins, the causes of which remain uncertain. Human-induced changes in the IPWP have important implications for understanding and projecting related changes in monsoonal rainfall, and frequency or intensity of tropical storms, which have profound socioeconomic consequences.
authors.affiliation: School of Environmental Science and Engineering, Pohang University of Science and Technology, Pohang 37673, South Korea.
authors.forename: Evan
authors.initials: E
authors.lastname: Weller
authors.affiliation: School of Environmental Science and Engineering, Pohang University of Science and Technology, Pohang 37673, South Korea.
authors.forename: Seung-Ki
authors.initials: SK
authors.lastname: Min
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation Marine and Atmospheric Research, Aspendale, Victoria 3195, Australia.; Physical Oceanography Laboratory, Qingdao Collaborative Innovation Center of Marine Science and Technology, Ocean University of China, Qingdao 266071, China.
authors.forename: Wenju
authors.initials: W
authors.lastname: Cai
authors.affiliation: Pacific Climate Impacts Consortium, University of Victoria, Victoria, British Columbia V8W 2Y2, Canada.
authors.forename: Francis W
authors.initials: FW
authors.lastname: Zwiers
authors.affiliation: School of Environmental Science and Engineering, Pohang University of Science and Technology, Pohang 37673, South Korea.
authors.forename: Yeon-Hee
authors.initials: YH
authors.lastname: Kim
authors.affiliation: School of Environmental Science and Engineering, Pohang University of Science and Technology, Pohang 37673, South Korea.
authors.forename: Donghyun
authors.identifier: 0000-0003-0184-2712
authors.initials: D
authors.lastname: Lee
mesh_terms: D002980:Climate; D059000:El Nino-Southern Oscillation; D057232:Global Warming; D017752:Greenhouse Effect; D006801:Humans; D019156:Indian Ocean; D008962:Models, Theoretical; D010140:Pacific Ocean; D012623:Seawater; D013696:Temperature
keywords: Indo-Pacific warm pool; Pacific decadal oscillation; climate models; greenhouse-gas forcing; sea surface temperature