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

Abstract

The Indo-Pacific Warm Pool (IPWP) is the warmest ocean enclosed by 28°C of sea surface temperature (SST) in the Indian and western Pacific Ocean (Clement et al., 2005). The IPWP plays a key role as a heat engine of global climate due to its enormous evaporation, convection, and vast latent heat release to the atmosphere (De Deckker, 2016). It also contributes to regional hydrological cycles, including the Asian monsoon (Annamalai

On the differential expansion speeds of Indo-Pacific warm pool and deep convection favoring pool under greenhouse warming

“…As a result, the large OWPSST=28 area change contradicts the small DCFP area change, implying that the OWPSST=28 expansion speed based on the fixed 28°C threshold is not equivalent to the increase in potential of deep convection occurrence over the Indo-Pacific Ocean. This suggests, in the context of the IPWP inducing climate responses through favoring atmospheric deep convection, that the impacts of IPWP expansion on the global climate may be overestimated if the changing relationship between SST and deep convection under global warming is not considered 9,17,19 . The agreement between the changes in DCFP and deep convection area confirms that the DCFP area change acts as a more reasonable measure for studying the climate effects generated by the Indo-Pacific Ocean warming indicator of IPWP expansion and suggests the necessity of taking the σSST_conv variability into account when studying the long-term variability of the IPWP.…”

“…Furthermore, under different shared socio-economic pathway (SSP) scenarios, numerical climate models projected that the global average SST will increase by 0.86°C (SSP1-2.6) to 2.89°C (SSP5-8.5) from 1995-2014 to 2081-2100 26 , which will result in almost the whole tropical ocean being warmer than 28.0°C by the end of the 21 st century under the SSP5-8.5 scenario 17,27 . In such sense, on one hand, according to the traditional IPWP definition, the OWPSST=28 would cover most of the tropical-wide ocean; on the other hand, the significant tropical ocean warming also indicates the possibility of an further increase in σSST_conv 20 , implying that some parts of the projected OWPSST=28 may not be featured with deep convection activity or even be covered by atmospheric subsidence, such as the eastern Pacific region 17,18,28 . This disagrees with the definition of the IPWP (or OWPSST=28) which considers constant SST=28°C as the threshold for deep convection.…”

“…Because of the IPWP's importance to the global climate system, changes in the IPWP area have implications for the climate response to greenhouse warming. Researchers have been paying close attention to the changes in the IPWP size in recent decades, and it was reported that the IPWP size has been expanding significantly in the past century as the global ocean sea surface temperature (SST) increases under anthropogenic greenhouse warming 1,9,[17][18][19] . For example, Hoyos and Webster (2012) reported that the observed global oceanic warm pool expanded from about 4.0 to 7.0 10 7 km 2 during 1920-2000, and the climate model-projected warm pool area increases by 2100 were greater than 70% and 90% relatively to the 2000-2004, under the IPCC A1B and A2 scenario, respectively 18 .…”

“…These prior publications suggested a disagreement of the area changes between OWPSST=28 and atmospheric convection over the Indo-Pacific Ocean. However, despite some discussion on the variability of σSST_conv in a global aspect 9,18,20,21,24,25,29 , many latest relevant research still stick to the traditional IPWP definition 9,[17][18][19]…”

Differential expansion speeds of Indo-Pacific warm pool and deep convection favoring pool under greenhouse warming

“…Because of the IPWP's importance to the global climate system, changes in the IPWP area have implications for the climate response to greenhouse warming. Researchers have been paying close attention to the changes in the IPWP size in recent decades, and it was reported that the IPWP size has been expanding significantly in the past century as the global sea surface temperature (SST) increases under anthropogenic greenhouse warming 1,9,[17][18][19] . For example, Hoyos and Webster (2012) reported that the observed global oceanic warm pool expanded from about 4.0-7.0 × 10 7 km 2 during 1920-2000, and the climate model-projected warm pool area increases by 2100 were greater than 70% and 90% relatively to the 2000-2004, under the IPCC A1B and A2 scenario, respectively 18 .…”