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Climatically, the South Pacific has a variety of climates ranging from the warm, rainy, year-round equatorial climate of the Solomon Islands to a tropical to subtropical climate with alternating hot and humid and cooler and drier seasons. This area is located on one of the most important convection zones on the planet, the South Pacific Convergence Zone (SPCZ), with direct consequences in terms of floods, droughts, heat waves and cyclones on the South Pacific islands. The SPCZ is a key component of cyclone formation and governs the freshwater resources of South Pacific island countries at the first order of magnitude. On interannual scales, the intensity and position of the SPCZ are dependent on key climate phenomena in the region such as the El Niño-Southern Oscillation (ENSO).

The functioning of the SPCZ is challenging to understand because of the complex interactions that occur within it between the ocean and the atmosphere. International programmes, such as CLIVAR[1], to better understand the dynamics, interaction and predictability of the climate system have highlighted the complexity of the functioning of the SPCZ, which climate models generally simulate very poorly.

As a result of the SPCZ, Pacific Island States and Territories are profoundly affected by a number of weather and extreme events causing significant socio-economic and ecological damage. With very uneven adaptive capacities, given the diversity of geographical, economic and social situations, and with various future changes in climatic events such as ENSO or extremes, the Pacific Island States and Territories are thus very vulnerable to the effects of climate change, even though they represent only 0.03% of global greenhouse gas (GHG) emissions.

Addressing current scientific
gaps and barriers

© Thierry Vogenstahl

It is noted that the global climate models, whose simulations have been used for decades as a basis for the IPCC reports, show, in the region, a strong disparity in the simulations of the SPCZ over the historical period (1970-2020) on the one hand, but also large uncertainties on its future positions and intensities (Brown et al., 2020) whatever the socio-economic scenario followed in the 21st century. These uncertainties carry over into assessing the future of key phenomena such as ENSO but also of extremes more generally (cyclones, heat waves, extreme rainfall events, droughts, etc.).  While it is accepted that the frequency of cyclones will decrease in the region, with a high degree of uncertainty according to the studies, their intensity is still being debated (Dutheil et al., 2020; Dutheil, 2019; Walsh et al., 2012, 2016). Finally, other extremes, such as heat waves and temperature records, are known to increase in the future (Power and Delage, 2019), but a reliable quantification of them remains to be estimated, given the biases of models in the South Pacific and the diversity of possible future scenarios.

These uncertainties about the future of the South Pacific climate, in general, carry over to the island level and, more particularly, to the high islands such as New Caledonia, Vanuatu and French Polynesia due to the inadequacy of these models, which are coarse spatial gridded (~100km) and unable to reproduce many local phenomena resulting from interactions with the complex topography of the islands. For all these island territories and countries, most climate models do not have a point of land at the location of the island territories. Therefore, they are not relevant for understanding the fate of the local climate and its impacts.

Thus there are no robust estimates of the fate of precipitation and drought at scales relevant to countries and territories under different scenarios over the next 100 years, nor the future of heat waves to slow climate trends. Yet the South Pacific islands are, for example, very vulnerable to the amount of precipitation that will dictate the availability of water resources.

All the uncertainties mentioned above raise the question of the reliability and relevance of climate projections in the South Pacific and the island states and territories scales in the current state of existing studies.

© crédit photo

Regional and national climate change adaptation strategies

On the front line of climate change, the island states and territories of the South Pacific are experimental areas at the forefront of the fight against climate change due to their exposure and high vulnerability to weather phenomena.

As part of their adaptation and mitigation plans, the Pacific island territories repeatedly express their need to acquire general knowledge about the future climate, particularly for managing their water, energy, and food resources and public health and biodiversity issues.

To adapt to these climate changes, it is necessary to know the future climate in detail, locally, to assess vulnerabilities and organise a coherent and structured response, i.e. changes in ways of doing things and living.

Action strategies, commonly known as National Adaptation Plans (NAPs), have already been carried out in many geographies, but this is not the case in the French Overseas Territories. The Wallis and Futuna adaptation strategy needs to be updated and translated into an action plan, and the Vanuatu adaptation plan is ancient.

To inform the adaptation strategies and plans of these island states and territories, a range of data, measures and potential investments that make societies more resilient to climate change needed to be implemented.