El Niño Southern Oscillation (ENSO)

ENSO, also known as the El Niño Southern Oscillation is a yearly fluctuation between the trade wind and Sea Surface Temperatures (SSTs) that alter the global climate. ENSO is classified under three phases: El Niño, La Niña, and Neutral. These phases fluctuate in regard to intensity and duration and are highly dependent on SSTs and thermocline. Additionally, the combination of wind fields and heat flux forcing affects the ENSO phases and their respective asymmetric evolutions (Chen et al. 2016). El Niño, which is the warm phase, has warmer than normal SSTs in the Eastern and Central Equatorial Pacific (Bayr et al. 2021). The warm advection from the eastward zonal current anomalies in the equatorial Eastern Pacific causes anomalous downwelling and warm vertical advection (Chen et al. 2016). Therefore, high upper ocean heat content and eastward advection of warm water are influenced by the warm SST anomalies (Bayr et al. 2021). In contrast, the oscillation of cold SSTs from the equatorial central Pacific and warm SSTs from the West Pacific to the Central North Pacific results in a strong La Niña (Hoell and Funk 2013). La Niña, which is known as the cold phase, has colder than normal SSTs in the eastern and central equatorial Pacific (Bayr et al. 2021). During the La Niña, cold advection from the westward zonal current anomalies in the Eastern Equatorial Pacific causes anomalous upwelling and cold vertical advection (Chen et al. 2016). Therefore, low upper ocean heat content and westward advection of cold water are influenced by the warm SST anomalies (Bayr et al. 2021). The last phase is the Neutral phase, which is seen as a node as the transition point between the two extremes. The Neutral phase is near normal climate conditions for the region, however, the neutral years tend to take on less intensified characteristics of the absolute spectrum ENSO (NOAA Pacific RISA 2015). 

The current trend for ENSO is more warming SSTs anomalies in the tropical Central Pacific with predictions of different seasonal evolution and teleconnection patterns (Yang et al. 2018). Some climate models suggest that long-term changes are similar to La Niña. However, these long-term results could change if the Central Pacific warms faster than the West Pacific because evaporative cooling at the surface will increase over the West Pacific while warming via vertical thermal advection will decrease (Hoell and Funk 2013). In contrast, some future predictions indicate a more strong El Ni ̃no based on historical shallow equatorial Pacific thermocline displaced upwelling being more centered to the tropical central Pacific, which influences ENSO events catered toward the central Pacific as well. While both suggest different phases, the main trend is to have more warmer SSTs located in the central Pacific. While further research is needed for a more accurately predicted evolution of ENSO and its influence on climate change, some models indicate a trend toward more El Niño conditions and stronger, colder events due to global warming from anthropogenic and natural sources (Yang et al. 2018). Predictive forecasts that use long-term statistical models for rainfall and sea level forecasts due to ENSO for these islands can provide much-needed support in the form of adaptation and mitigation strategies to help combat the intensified effects and hazards of ENSO. These statistical models form probable impact scenarios and ENSO evolution that result in constant monthly discussions between Pacific island weather offices. Ultimately, there is a need for more research on these areas, but the current methods to combat climate change through climate modeling is useful enough to help other vulnerable regions for now (Chiang et al. 2009). The advocacy for more research about ENSO and climate change can effectively revise mitigation and adaptation strategies, especially for vulnerable tropical island communities. 

Oceanic Regions and their Pacific Islands

Pacific islands are vulnerable communities based on their geographical remoteness, high dependency on trade for livelihood, vulnerability to economic shocks, and high susceptibility to climate change hazards. These climate change hazards include sea level rise, intensified tropical cyclones, prolonged droughts, heatwaves, and forest fires (Schroeder et al. 2012; Abraham et al. 2022). These tropical islands are rich biodiversity hotspots with local native plants and vegetation, coral-enriched oceans, and high fish population patterns (Abraham et al. 2022). The majority of Pacific islanders live within 5 km of the coast, putting them in high-risk areas for extreme weather events impacts (Mycoo et al. 2022). Thus, small Pacific islands and their ecosystems are more vulnerable to climate change (Lefale 2010). Hawaii and the U.S Affiliated Pacific Islands composed of Guam, the Commonwealth of the Northern Mariana Islands, the Republic of Palau, Marshall Islands, Federated States of Micronesia, and American Samoa seen in Figure ?? tend to be overlooked in research (Schroeder et al. 2012). Guam is a small island in the western Pacific where extreme rainfall and flooding can have great impacts. One study analyzed extreme annual maximum precipitation in Guam using intensity-duration-frequency (IDF) curves. The results show extreme rainfall is highly dependent on extreme weather events, for instance, typhoons impact increased daily IDF curves by 3% for the island (Yeo et al. 2022). El Ni ̃no-like SST variations can result in increased forest fires, drier conditions, altered fishing habits, prolonged droughts, flash floods associated with increased tropical cyclones, lowered sea levels, colder ocean conditions, and food shortages for the western Pacific. In contrast, the eastern Pacific experiences more rainfall and reduced nutrient-rich upwelling associated with weakening currents along the West Coast of the Americas (Schroeder et al. 2012). It is worth noting that mean state changes that look El Ni ̃no-like produce similar impacts on precipitation in the Pacific. With the impacts of climate change, high confidence exists that vulnerability will increase for oceanic regions and their islands (Schroeder et al. 2012; Mycoo et al. 2022). The climate change impacts on islands are seen through SST warming, sea level rise, salinity increases to water supplies, biodiversity reduction, ocean acidification, coral bleaching, intensified storms, negative production of island agriculture, and drastic hydrological changes (Abraham et al. 2022). One study that evaluated Guam IDF curves from extreme rainfall patterns noted the need for a better understanding to improve storm-water manager systems and hazard mitigation (Yeo et al. 2022). Another study investigated Samoa’s forecasting strategies for cloud types and tropical cyclones. The study calls for the need for a better synthesis of contemporary Western scientific methodologies of weather and climate with indigenous forecasting practices to help improve weather education, especially with climate change (Lefale 2010). Projections for the tropics can provide much-needed support in the form of adaptation and mitigation strategies to help combat the intensified effects and hazards of global climate and circulation changes associated with mean state changes and also changes to modes of variability such as ENSO (Mycoo et al. 2022). 

What's Been Done So Far? What Should Be Done?

Currently, a great deal of foreign aid has been given to the region to help combat extreme climate change and build better infrastructure. The United States Agency for International Development has contributed more than 500 million dollars across the Pacific Islands to address the impact of climate change, as well as improve disaster preparedness (U.S. Agency for International Development, 2023). The World Health Organization (WHO) has also contributed to protecting infrastructure, especially hospitals, power plants, and water sanitation so that critical areas are more resilient to change (World Health Organization, 2018). However, foreign aid can also result in an over-reliance on other governments to support these countries as infrastructure is damaged by climate change, such as through hurricanes or changing sea levels. A Georgetown publication highlighted this particular issue, noting that much foreign money is lost in transit through corruption (Kelman, 2023). Some Polynesian governments have proposed a "loss and damage" fee that would be paid by countries with large greenhouse gas emissions as a way of supporting the countries in the area while reducing aid dependency and encouraging the development of carbon-neutral infrastructure around the world (Kelman, 2023). Another area that has experienced some success is creating local education programs that produce environmental scientists who can understand the issue from a new perspective. The Partnership for Advanced Marine and Environmental Science Training supports 5 different University programs for Environmental Science across Polynesia (Parsons, 2022). These programs have produced scientists and professors who are now working to encourage others to protect the area against drastic weather changes. The area is still critically vulnerable to rising sea levels, worsening weather patterns, droughts, hurricanes, and all manner of issues brought on by climate change and inclement weather. Focusing on how that weather could change will allow us to produce plans to combat those issues before they can do further damage. 

Conclusions

The CESM2 large ensemble under the SSP370 forcing scenario is used to assess how the pattern of SST change in a warmer climate impacts weather signals. The impact of SST pattern change on the mean precipitation and wind amplitude change for specific tropical islands and oceanic regions is important. Islands distributed across the tropical Pacific have various magnitudes of mean precipitation change for each individual station. These results highlight the challenges in predicting water resource availability for tropical islands in the future. Climate action through adaptation and mitigation strategies can help overcome adversity in climate change hazards given this uncertainty. Climate action can be a needed step to reduce the impact of climate change on communities through mitigation, adaptation, or geoengineering strategies. Mitigation takes proactive steps to reduce unnecessary amplification of severe climate hazards, while adaptation strategies create suitable living biotic or geoengineering methods to cohabit with climate change hazards. Pacific islands and their respective weather offices organize the Pacific ENSO Applications Center (PEAC) to forecast precipitation and sea level (Schroeder et al. 2012), which might play a role in helping the islands prepare for climate change and its impacts. The limitations to climate change preparedness for islands are rooted in financial and political governance, lack of weather education with some due to cultural beliefs, high susceptibility to economic shock, and inadequate climate data for these regions (Mycoo et al. 2022). Thus, PEAC’s strategy is to foster collaborative efforts to overcome these adversities, prepare for the necessary mitigation and adaptation strategies, and improve public awareness of oceanic regions (Schroeder et al. 2012). Island climate change preparedness ranges from coastal protection structures such as sea walls, and elevated homes, improving agroforestry, reef restoration, planting native plants for beach erosion reduction, better fishing technologies and equipment, and diversifying (salt tolerant) crops (Mycoo et al. 2022). 

Questions - What Are We Looking to Find?

Historical

1) How have El Niño and La Niña years impacted the Oceanic regions?

2) What has been the past patterns of El Niño and La Niña intensity?

3) Have recent environmental efforts such as adaptation, geo-engineering, or mitigation strategies produced any significant changes regarding to climate?

4) Based on historical reanalysis data, which islands in the Oceanic regions have been the most and least impacted?

Predictive

5) Depending on the degree that climate change were to be altered in the future, would ENSO severely affect the oceanic regions? If so, to what extent?

6) What are the primary meteorological variables to severely impact the oceanic regions based on magnitude?

7) How does the historical reanalysis data of the Oceanic Regions and their associated islands compare to its predictive data?

8) Based on predictive data, which islands in the Oceanic regions would be the most and least impacted?

9) To what extent do climate change influence the magnitude of El Niño and La Niña in a warmer climate?

10) Based on predictive data, what are some socioeconomic aspects of the Oceanic regions that could be worsen by climate change?