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Australia; New Zealand; Pacific
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Ocean warming, marine heatwaves and sea-level rise pose increasing risk in South-West Pacific region
- 2025 was the 2nd warmest year on record for the South-West Pacific region
- Marine heatwaves disrupted ecosystems and fisheries
- Indonesia's last tropical glacier is just 2% of its 1988 size, may disappear in 2026
- Rare tropical cyclone killed more than 1,200 people in Indonesia and Malaysia
- Early warnings and early action save lives, but critical coordination and capacity gaps remain
SINGAPORE/GENEVA, 7 July 2026 (WMO) – The vast ocean expanse in the South-West Pacific is becoming hotter and more acidic, harming local economies and marine ecosystems, whilst rising sea levels threaten vulnerable coastal communities and low-lying island nations, according to a new report from the World Meteorological Organization (WMO).
The State of the Climate in the South-West Pacific 2025 report documents how the region had its second warmest year on record (behind 2024), with extreme weather causing widespread disruption, economic damage, and loss of life. The deadliest single event was Cyclone Senyar, the first known system to reach tropical cyclone intensity in the Strait of Malacca, which impacted more than 10 million people in Indonesia and Malaysia and killed more than 1 200.
In 2025, the remaining tropical ice cover in Papua, Indonesia, was estimated to be only about 2% of the ice area observed in 1988. The last remaining tropical glacier of the region is expected to disappear by the end of 2026 or early 2027, according to the report.
“For many countries and territories in the South-West Pacific, the ocean is central to livelihoods, economies and resilience. 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,” said WMO Secretary-General Celeste Saulo.
The State of the Climate in the South-West Pacific 2025 report includes contributions from National Meteorological and Hydrological Services, climate and ocean experts and United Nations and other international partners. It is one of a series of regional reports by WMO to provide scientific support for climate-smart decision-making and disaster risk reduction.
“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. Early warning and early action save lives when alerts are timely, messages are trusted and last-mile delivery reaches the vulnerable,” said Armida Salsiah Alisjahbana, Executive Secretary of the United Nations Economic and Social Commission for Asia and the Pacific (ESCAP).
The report was released during the Southeast Asia Marine Heatwaves Services Workshop in Singapore, 7-10 July 2026, organized by the Association of Southeast Asian Nations (ASEAN) Specialised Meteorological Centre (ASMC). Marine heatwave forecast products help provide critical early warning and give users weeks to months to prepare for potential impacts.
Temperature
The annual mean surface air temperature averaged over both land and ocean areas in 2025 in the South-West Pacific region ranked as the second highest on record, at about 0.37 °C above the 1991–2020 average.
There were warmer-than-average temperatures in the western Pacific and below-average temperatures over the central tropical Pacific – typical of La Niña conditions.
Ocean heat and sea-surface temperature
Long‑term ocean warming has led to more frequent, longer lasting and more intense marine heatwaves, with serious consequences for marine ecosystems and the communities and0 industries that depend on them.
In 2025, record high ocean heat content (in the upper 700 m of the ocean) was observed for the area south of Australia and in the southern Tasman Sea, as well in some parts of the tropical North Pacific between the Philippines and Hawaii, and locally south of Sumatra (Indonesia).
La Niña temporarily cooled sea surface temperatures in some parts of the South-West Pacific in 2025 but the average for the whole South-West Pacific region remained high. They were at record levels over a broad area of the tropical western North Pacific (extending from east of the Philippines to Hawaii), around Papua New Guinea, and in Australia region as a whole.
Marine heatwaves are prolonged periods of extreme heat that affect the ocean and have a range of consequences for marine life and dependent communities. They cause widespread coral bleaching, fish deaths, major disruptions to aquaculture operations, kelp forest mortality, shifts in species distributions and harmful algal blooms.
Marine heatwave coverage in 2025 – whilst lower than the previous year - was the most extensive ever recorded in a year without an El Niño event. This is a worrisome sign for 2026, with a potentially strong El Niño event now developing.
The most significant areas with severe and extreme heatwaves in 2025 were between the Maritime Continent and the coast of Australia, and in the western South Pacific in the area between New Zealand, New Caledonia, and Vanuatu.
Specifically, during summer 2024/2025, extensive marine heatwave conditions affected northern Australia, the west coast, the Great Australian Bight and southern waters. This contributed to coral bleaching in both the eastern and western reef systems, the first time this has happened in both systems in the same season, highlighting the escalating risk and the need for effective early warning services.
The report has a special case study on the operational marine heatwave prediction services being rolled out in Australia by he Australian Bureau of Meteorology, in partnership with the Commonwealth Scientific and Industrial Research Organisation (CSIRO). The service was designed to transition marine heatwave research into an operational climate service to support preparedness and risk‑based decision‑making for marine sectors.
Sea-level rise
Sea level rises in response to ocean warming (via thermal expansion) and the melting of glaciers, ice caps and ice sheets, thereby affecting the lives and livelihoods of coastal communities and low-lying island nations.
Over the period 1999–2025, sea level rose at an average rate of 3.7 ± 0.03 mm per year in the South-West Pacific region. An elongated pattern of high rates of sea-level rise has been observed from the eastern coast of Australia to about 120°W longitude, encompassing the Coral and Tasman Seas and a large area west of New Zealand.
Ocean acidification
Ocean waters are becoming more acidic as a result of absorbing increasing amounts of carbon dioxide. Ocean acidification, together with ocean warming and deoxygenation, is affecting marine ecosystems, habitats and biodiversity.
Almost the entire South-West Pacific region experienced record low values for surface ocean pH in 2025.
Extreme Weather
As is typical during La Niña conditions, rainfall was above average across much of the Maritime Continent, with many regions recording precipitation within the wettest 10% of years between 1991 and 2020, while much of the western and central equatorial Pacific was drier than average.
Several countries experienced extreme weather and climate events with fatalities and significant economic losses – especially from tropical cyclones.
Cyclone Senyar was the first tropical cyclone on record in the Strait of Malacca since 1886 and made a first made landfall in northern Sumatra on 26 November before recrossing the Strait and making a second landfall over Peninsular Malaysia. The most extreme rainfall was observed in the far north of Sumatra, Indonesia, (more than 400 mm in one day), northern Peninsular Malaysia and southern Thailand.
The report includes a case study on impacts and responses on this cyclone. It shows how early warnings, collaboration, and local grants reduced casualties and aided rapid relief. However, there were gaps in last-mile dissemination of warnings to some coastal populations and fishers.
Cyclone Senyar demonstrated the urgent need for impact-based forecasting of cascading hazards and to prepare for complex scenarios where cyclonic storms combined with monsoon surges trigger simultaneous floods, landslides and debris flows and may even coincide with geophysical hazards such as earthquakes or tsunamis.
Notes for Editors
The State of the Climate in the South-West Pacific 2025 report was produced by WMO in collaboration with National Meteorological and Hydrological Services, international data centres, leading climate research and marine services institutions, and United Nations partners, including ESCAP, the Food and Agriculture Organization of the United Nations, and the World Food Programme.
WMO wishes to thank all contributors and partners, especially Thea Turkington, co-lead author, Meteorological Service Singapore and Blair Trewin, co-lead author, Bureau of Meteorology, Australia.
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Professor Sandra Morrison (Ngāti Rārua; Ngāti Maniapoto; Ngāti Whakaue), Faculty of Māori and Indigenous Studies, University of Waikato
"The release of the WMO report on the State of the Climate in South-West Pacific 2025 carries sobering messages of the impact of climate change and extreme weather disruption.
"With a region that is a mix of larger, mountainous continental islands and oceanic islands ranging from volcanic peaks to low-lying coral atolls, it is a complex region with its diverse marine and island ecosystems, tropical to temperate climates, and deep ocean circulation patterns that directly influence weather systems like El Niño
and tropical cyclones.
"Three key messages from the report state that first, 2025 was the second-warmest year on record in the South-West Pacific region, at 0.37 °C above the 1991–2020 average. Second, that the average sea-surface temperature for the region was the second highest on record, slightly below the record set in 2024. And third, that sea level continued to rise across the South-West Pacific, affecting coastal communities and low-lying island nations. While these drivers are not new, we know that any increase in temperatures will have devastating impacts on the environment and people alike which this report outlines with significant detailed evidence.
"The purpose of the WMO is not only to report and exchange data but also to help the public understand it. The case studies referenced therefore give real world examples of the drivers of climate change in the South-West Pacific, the impacts on environmental and human systems and a helpful guide of lessons learnt. Such
lessons point to investment in systems that give early warnings to enable planning for predicted weather events, the power of collaboration across stakeholder groups and ensuring good relationships with the users of the data.
"One criticism that I would make would be the need to ensure the inclusion of Indigenous knowledges in a region that has significant Indigenous populations. Indigenous populations are working alongside scientists in creating long term sustainable adaptation strategies which has critical benefits for all populations."
James Renwick, Professor of Climate Science & Physical Geography, Victoria University of Wellington | Te Herenga Waka
“The State of the Climate in the Pacific is a very welcome publication from the World Meteorological Organization, as the tropical South-West Pacific is usually poorly-represented in published material about the climate and how it is changing. We see human-induced warming here as we do globally. I am sorry to know the last tropical glacier in the mountains of Papua New Guinea is expected to be gone in the coming year, a permanent change to the landscape. Glacier loss carries on apace here in New Zealand as well, 42% of ice gone between 2005 and 2023, with snow accumulations generally down.
“New Zealand had its warmest spring on record in 2025, contributing strongly to ice loss and to the massive fire in Tongariro National Park. All of the effects of climate change are being felt strongly across the SW Pacific – warming, sea level rise, ocean acidification, intensifying tropical cyclones, marine heatwaves. The only way to combat increases in extremes and the loss of ice & snow is to reduce emissions of greenhouse gases, but there’s little sign of that yet.
“The prolonged La Niña clearly influenced tropical climate across the Pacific last year. This year’s ‘super’ El Niño is bound to bring stresses, dry conditions in the west and much wetter conditions in the central and eastern Pacific, all pumped up by climate change.”
Associate Professor Daniel Kingston, School of Geography | Te Iho Whenua, University of Otago | Ōtākou Whakaihu Waka
"The WMO retrospective on climate in the southwest Pacific region for 2025 treads similar ground to previous reports, while also containing some interesting (and alarming) statistics.
"As for the world as a whole, 2025 was the second warmest on record in the southwest Pacific. The world continues to hover around the 1.5 °C warming threshold that has been linked to dangerous climate change impacts.
"What’s notable in this case is that this warmth has occurred despite the presence of a La Niña event – which often acts to reduce overall temperatures in the southwest Pacific. 2025 was actually the warmest year that has occurred in this region without the presence of El Niño conditions – noteworthy in light of the El Niño event this is just beginning to unfold now.
"The report devotes some attention to the impacts of this warmth on snow and ice. The remaining tropical glaciers in this region (in New Guinea) are likely to completely disappear either this year or next, while the report notes that glacier volume in New Zealand has decreased by 42% between 2005 and 2023.
"Details about various marine heatwaves (MHW) are also included. Although 2025 was not a record year for overall MHW extent, recent increases are dramatic: most of the past 10 years have had more than double the coverage of MHW compared to the 1990s and early 2000s."
Associate Professor Heather Purdie, School of Earth & Environment, University of Canterbury
“For those of us who work on snow and ice, the most recent State of the Climate Report for the South West Pacific by the World Meteorological Organisation, sadly, held no surprises.
"I have been monitoring glaciers in the mountains of Aotearoa New Zealand for more than two decades, watching and recording our ice volume shrinking away. We have already lost around 300 glaciers and more will follow, with a reported 42% decrease in glacier volume between 2005 and 2023.
"Glaciers are nourished by snowfall during the colder months, but increasingly we are seeing changes to snowfall patterns. As temperatures continue to rise, snow is arriving later and winter snowpacks are thinning. Even though our mountains generally receive significant snow fall in spring, these late top-ups are not enough to turn the tide on glacier loss.
"However, this year, strong El Niño conditions are developing in the Pacific, and while many eastern areas tend to be drier during El Niño, our glacier regions can experience increased precipitation and lower melt rates. But we will have to wait until the end of this coming summer to see how the glaciers have fared.”
Professor Karin Bryan, School of Environment and Institute of Marine Science, University of Auckland
“The State of the Climate report confirms what our local researchers are finding. I think the most concerning of all the indicators they review, is the steady creep upward of the ocean temperature. The viability of organisms and ecosystems is critically linked to temperature, and here we are seeing extremes become more of an everyday phenomenon. Many species are already under threat due to direct anthropogenic effects such as runoff, fishing and habitat change, and do not have the resilience any more to deal with this additional threat."
