The World Meteorological Organization (WMO) reports that 2025 was the second warmest year on record for the South-West Pacific, trailing only 2024. Average surface air temperatures reached approximately 0.37 °C above the 1991–2020 average, contributing to rising sea levels, marine heatwaves, and the loss of the region’s last tropical glacier.
Ocean Warming and Marine Heatwaves in 2025
Long-term ocean warming has increased the frequency, duration, and intensity of marine heatwaves across the South-West Pacific, according to the WMO. In 2025, the WMO observed record-high ocean heat content in the upper 700 meters of the ocean in the southern Tasman Sea, south of Australia, south of Sumatra in Indonesia, and the tropical North Pacific between Hawaii and the Philippines.
Average sea-surface temperatures remained high throughout the region. This occurred despite the cooling influence of the La Niña climate pattern in specific areas. Record temperatures were specifically noted around Papua New Guinea, the Australian region, and a broad expanse of the tropical western North Pacific. The WMO characterized the 2025 marine heatwave coverage as the most extensive ever recorded in a year without an El Niño event, which the agency describes as a worrisome sign for 2026 as a potentially strong El Niño develops.
Impact on Coral Reefs and Marine Ecosystems
Marine heatwaves trigger coral bleaching, fish deaths, and the loss of kelp forests. During the 2024/2025 summer, heat conditions around Australia contributed to coral bleaching in both the eastern and western reef systems in the same season for the first time. The WMO notes these events disrupt aquaculture and shift species distribution, which threatens food security and local economies.
The region also faced chemical changes in the water. In 2025, almost the entire South-West Pacific recorded historically low surface ocean pH values. This acidification happens as seawater absorbs increasing amounts of carbon dioxide.
Rising Sea Levels and Glacial Loss
Sea levels in the South-West Pacific rose at an average rate of 3.7 ± 0.03 millimeters per year between 1999 and 2025. The WMO identified a specific area of especially high sea-level rise stretching from Australia’s eastern coast to approximately 120°W longitude, encompassing the Tasman and Coral Seas and areas west of New Zealand.
The report also highlights the critical state of tropical ice. The region’s last remaining tropical glacier, located in Indonesia, may disappear by the end of this year or early 2027. Current data shows the remaining ice cover is only about two percent of the size it was in 1988.
Cyclone Senyar: The Deadliest Event of the Year
Cyclone Senyar was the deadliest single weather event of 2025. It was the first known system to reach tropical cyclone intensity within the Strait of Malacca. According to the WMO, the storm affected more than 10 million people in Malaysia and Indonesia, resulting in more than 1,200 deaths.
The storm produced extreme precipitation, with far northern Sumatra recording more than 400 millimeters of rain in a single day. Heavy rainfall also impacted southern Thailand and northern Peninsular Malaysia.
The Role of Early Warning Systems
WMO Secretary-General Celeste Saulo stated that the ocean is central to the resilience and livelihoods of many countries in the South-West Pacific. Armida Salsiah Alisjahbana, the ESCAP Executive Secretary, noted that intensifying heat is placing new pressures on public health, infrastructure, and food systems.
The WMO produced this report in collaboration with international data centers, national meteorological and hydrological services, and UN partners including ESCAP. Alisjahbana emphasized that timely alerts and trusted messaging are essential for “last-mile delivery” to reach vulnerable populations and save lives.
- Temperature: 0.37 °C above 1991–2020 average.
- Sea-Level Rise: 3.7 ± 0.03 mm/year (1999–2025).
- Glacial Loss: Indonesia’s tropical glacier is at 2% of its 1988 size.
- Major Event: Cyclone Senyar (1,200+ deaths; 10 million affected).