This report draws together the findings of five country case studies on sea level rise commissioned by the Commonwealth Secretariat’s Climate Change and Oceans Directorate and updated in 2026: Guyana, Kiribati, Papua New Guinea, Tonga and Tuvalu. Spanning a low-lying mainland coastal plain in South America and four Pacific small island developing states (SIDS), the five studies together offer a comparative view of how Commonwealth coastal nations are experiencing, and responding to, rising seas.
Three findings cut across every country. First, sea level rise is being felt now, and faster than the global mean: observed local rates range from roughly 5 mm per year in Tuvalu and Kiribati to 7.3mm per year in Tonga and 4.7–10.2mm per year in Guyana. In each case, this is well above the global average of approximately 3.2–3.5mm per year, and is amplified locally by land subsidence, tectonics and coastal erosion. Second, exposure is extreme and concentrated: between 59 per cent of people (PNG) and the entire population (Tuvalu) live in the coastal zone, alongside the bulk of national assets, infrastructure and economic activity. Third, none of the five countries yet has adaptation governance and finance arrangements adequate enough to deal with the scale of the threat.
The studies also reveal a consistent set of constraints – fragmented legal and institutional frameworks, weak vertical and horizontal co-ordination, heavy dependence on donor finance, persistent gaps between planning and implementation, logistical barriers to reaching remote communities, and thin monitoring and evaluation. Equally, they surface transferable good practice: ecosystem-based adaptation (notably mangroves) integrated with hard infrastructure, the mainstreaming of adaptation into national development planning, dedicated climate finance vehicles such as Tonga’s Climate Change Trust Fund, and the institutionalisation of adaptation capacity, as in Tuvalu’s move to establish a Coastal Management Authority.
The present report closes with cross-cutting recommendations for member countries and for the Secretariat’s continued technical assistance under the Commonwealth Blue Charter.
