The latest State of the Climate in the South-West Pacific report found that 2025 was the second warmest year on record for the region, behind 2024, with average surface air temperature about 0.37 °C above the 1991–2020 average.
The report documents how rising sea levels threaten low-lying island nations and coastal settlements – while marine heatwaves and ocean acidification are damaging ecosystems critical for food security, tourism, fisheries and local economies.
A stark picture
It warned that the region’s last remaining tropical glacier – located in Indonesia – may disappear by the end of this year or early 2027 as the remaining tropical ice cover is only about two per cent of the size observed in 1988.
“For many countries and territories in the Southwest Pacific, the ocean is central to livelihoods, economies and resilience,” said WMO Secretary-General Celeste Saulo.
“In 2025, the region experienced warming oceans, rising sea levels, marine heatwaves and ocean acidification, alongside tropical cyclones and the continued loss of tropical glacier ice.”
Oceans under pressure
WMO said long-term ocean warming has made marine heatwaves more frequent, longer lasting and more intense.
In 2025, record-high ocean heat content in the upper 700 metres of the ocean was observed south of Australia and in the southern Tasman Sea, as well as in parts of the tropical North Pacific between the Philippines and Hawaii and locally south of Sumatra in Indonesia.
Average sea-surface temperatures remained high across the whole region despite the temporary cooling influence of the La Niña climate pattern in some areas, with record levels around Papua New Guinea, in the Australian region and across a broad area of the tropical western North Pacific extending from east of the Philippines to Hawaii.
Fisheries and ecosystems disrupted
Marine heatwaves can cause coral bleaching, fish deaths, major disruption to aquaculture, kelp forest loss, shifts in species distribution and harmful algal blooms, WMO explained.
Although marine heatwave coverage in 2025 was lower than the previous year, it still marked the most extensive ever recorded in a year without an El Niño event, which the agency called “a worrisome sign for 2026, with a potentially strong El Niño event now developing.”
During summer 2024/2025, marine heatwave conditions around Australia contributed to coral bleaching in both the eastern and western reef systems in the same season for the first time, highlighting the need for effective early warning services.
Rising sea levels
Sea levels also continued to rise in response to ocean warming. Between 1999 and 2025, sea level in the Southwest Pacific region increased at an average rate of 3.7 ± 0.03 millimetres per year.
The report identified an elongated area of especially high sea-level rise stretching from the eastern coast of Australia to around 120°W longitude, covering the Coral and Tasman Seas and a large area west of New Zealand.
Moreover, almost the entire Southwest Pacific recorded historically low surface ocean pH values in 2025, as seawater absorbed increasing amounts of carbon dioxide and became more acidic.
Deadly and destructive storm
The year’s deadliest single event was Cyclone Senyar, the first known system to reach tropical cyclone intensity in the Strait of Malacca. More than 10 million people in Indonesia and Malaysia were affected while more than 1,200 were killed.
The heaviest rainfall was recorded in far northern Sumatra, where more than 400 millimetres fell in one day, as well as in northern Peninsular Malaysia and southern Thailand.
Early warning saves lives
The report was produced by WMO in collaboration with national meteorological and hydrological services, international data centres, leading climate research and marine services institutions, and UN partners, including its regional Economic and Social Commission, ESCAP.
“Across Asia and the Pacific, heat is intensifying multi-hazard risks, intersecting with food systems, public health, infrastructure and oceans, and placing new pressures on health and livelihoods,” said Armida Salsiah Alisjahbana, the ESCAP Executive Secretary.
“Early warning and early action save lives when alerts are timely, messages are trusted and last-mile delivery reaches the vulnerable.”
