Assessment of 21st Century Changing Sea Surface Temperature, Rainfall, and Sea Surface Height Patterns in the Tropical Pacific Islands Using CMIP6 Greenhouse Warming Projections

Tropical Pacific Islands face unknown rates of future warming due to increased greenhouse gas emissions, but almost certain changing climate stresses. Continued global warming is projected to cause further changes to the mean conditions and variability of sea surface temperature (SST), rainfall, and sea surface height (SSH). Previous climate model simulations showed that the equatorial Pacific is likely to have greater increased rainfall, compared to elsewhere in the tropics. There is less certainty about future rainfall changes away from the equator, including around many of the numerous tropical Pacific Islands. Here, we assess the Coupled Model Intercomparison Project-phase 6 (CMIP6) as it relates to future changes of SST, rainfall, and SSH in the tropical Pacific. Focus is on the island regions of Hawaii, Guam, and American Samoa, as well as the Nino 3.4 region. We consider two development narratives of the 21st century by assessing the SSP2-4.5 and SSP5-8.5 experiments, and describe climate changes in the tropical Pacific relative to the recent historical conditions that are likely for either 1.5 degrees C or 3 degrees C of global mean surface temperature (GMST) warming above preindustrial levels. Consistent with prior-generation climate models, we find that future rainfall increases the most where SST warming is greatest, and also an overall increase of interannual variability associated with the El Nino-Southern Oscillation (ENSO) affecting rainfall and SSH. We describe changes in SST, rainfall, and SSH for particular warming amounts, and make comparisons with time-based climate assessments during the 21st century, which are relevant results toward better understanding uncertainty and supporting adaptation efforts in the tropical Pacific Islands.