Ocean temperatures reached another record high in 2025

Institute of Atmospheric Physics, Chinese Academy of Sciences

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A bleached coral reef forms the crumbling palace of a mythical underwater kingdom, while its legendary “shrimp soldiers and crab generals” face a modern crisis: the weakening of their very armor by ocean warming and acidification. The cover concept and shrimp/crab cartoon characters were suggested by Lijing Cheng; the background photograph of the bleached coral reef was taken by Jiang Zhu in Palawan, Philippines.

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Credit: Advances in Atmospheric Sciences

A new international analysis published in Advances in Atmospheric Sciences on 9 January finds that the Earth’s ocean stored more heat in 2025 than in any year since modern measurements began. The 2025 heat increase was 23 Zetta Joules (23,000,000,000,000,000,000,000 Joules of energy), which is equivalent to ~37 years of global primary energy consumption at the 2023 level (~620 Exa Joules per year). The finding is the result of a major international collaboration, involving more than 50 scientists from 31 research institutions worldwide.

Why are the oceans so important?

The ocean absorbs more than 90% of the excess heat trapped by greenhouse gases, making it the main heat reservoir of the climate system. Because ocean heat content (OHC) reflects the accumulation of heat stored in the ocean, it provides one of the best indicators of long-term climate change.

Study Results

The assessment combines data from major international data centers and independent research groups, including three observational products (Institute of Atmospheric Physics at the Chinese Academy of Sciences; Copernicus Marine; and NOAA/NCEI) and an ocean reanalysis (CIGAR-RT) from three continents: Asia, Europe, and America. These groups confirm that the 2025 OHC reached the highest level on record, confirming continued ocean heat gain.

The ocean warming is not uniform; some areas are warming faster than others. In 2025, about 16% of the global ocean area reached a record-high OHC, and about 33% ranked among the top three warmest values in their historical records. The warmest areas included the tropical and South Atlantic and North Pacific Oceans, and the Southern Ocean.

The overall re cord is characterized by stronger ocean warming trends since the 1990s than before. The increase in upper 2000m OHC is fairly steady in recent decades, though a small increase in rate can be detected. Ocean heat content reached a record high in 2025 as it has in each of the past nine years.

Ocean surface temperatures

Global annual mean sea-surface temperature (SST) in 2025 was the third warmest year in the instrumental record and remained about 0.5 °C (approximately 1°F) above the 1981–2010 average baseline. SST in 2025 is slightly lower than in 2023 and 2024, mainly due to the transition from El Niño to La Niña in the tropical Pacific. Sea surface temperatures are particularly important because they affect weather patterns worldwide. Warmer surface temperatures favor increased evaporation and heavier rains, thus causing more extreme tropical cyclones and weather events. These played a major role in widespread flooding and disruption throughout much of Southeast Asia, drought in the Middle East, and flooding in Mexico and the Pacific Northwest, in 2025.

Why does this matter?

Rising ocean heat drives global sea-level rise via thermal expansion, strengthens and prolongs heatwaves, and intensifies extreme weather by increasing heat and moisture in the atmosphere. As long as the Earth’s heat continues to increase, ocean heat content will continue to rise and records will continue to fall.

The final results will be included in a special collection on Ocean Heat Content Changes organized by the journal Advances in Atmospheric Sciences. Notably, the cartoon characters of the sad shrimp and crab on the cover were suggested by the study's corresponding author, Lijing Cheng from the Institute of Atmospheric Physics at the Chinese Academy of Sciences. 

"The idea comes from the 'shrimp soldiers and crab generals' guarding the underwater palace in Journey to the West," said Cheng. "We reimagined them not as mighty guardians, but as vulnerable creatures whose armor—their shells and scales—is under attack by ocean warming, acidification and other ocean environmental changes."

The collection will include various aspects of OHC changes and in-depth analyses of the mechanisms—for instance, regional OHC changes in the seas around China, the South Pacific, and the Indian Ocean. As leading climate scientist Kevin Trenberth  wrote in the preface of the special issue, it is structured as an ongoing collection, reflecting the evolving nature of climate science.

While the science continues to evolve, one conclusion remains clear: The biggest climate uncertainty is what humans decide to do. Together, we can reduce emissions, better prepare for upcoming changes, and help safeguard a future climate where humans can thrive.

Global ocean heat content changes for the upper 2000 meters of ocean waters since 1958.

Global ocean surface temperature changes since 1958

Credit

Pan et al.

Journal

Advances in Atmospheric Sciences

DOI

10.1007/s00376-026-5876-0 

Article Title

Ocean Heat Content Sets Another Record in 2025

Article Publication Date

9-Jan-2026

 

Clues from the past reveal the West Antarctic Ice Sheet’s vulnerability to warming

Ancient sediment records show the ice sheet retreated at least five times during warmer periods millions of years ago

University of Toyama

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By studying Pliocene sediments deposited when Earth was warmer than today, the researchers found that the West Antarctic Ice Sheet retreated far inland at least five times. These findings provide critical insight into how the ice sheet may respond to ongoing climate warming and the potential scale of future sea-level rise.

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Credit: Professor Keiji Horikawa from the University of Toyama, Japan

The Thwaites and Pine Island glaciers, located in the Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS), are among the fastest-melting glaciers on Earth. Together, they are losing ice more rapidly than any other part of Antarctica, raising serious concerns about the long-term stability of the ice sheet and its contribution to future sea-level rise.

To better understand the risks that warmer conditions pose to the WAIS, researchers are looking back to the Pliocene Epoch (5.3–2.58 million years ago), when global temperatures were about 3–4 °C higher than today and sea levels stood more than 15 meters higher, with melted ice from Antarctica contributing to much of that rise.

Now, examining a deep-sea sediment from this region, researchers from the IODP Exp379 Scientists, found that the WAIS margin retreated far inland at least five times during the Pliocene period.

The study was led by Professor Keiji Horikawa from the Faculty of Science, University of Toyama, Japan, and included Masao Iwai (Kochi University), Claus-Dieter Hillenbrand (British Antarctic Survey), Christine S. Siddoway (Colorado College), and Anna Ruth Halberstadt (University of Texas at Austin). The findings, made available online on December 22, 2025, and published in Vol. 123 of the journal PNAS on January 6, 2026, highlight the vulnerability of the WAIS to future warming.

“We wanted to investigate whether the WAIS fully disintegrated during the Pliocene, how often such events occurred, and what triggered them,” says Prof. Horikawa.

The team analyzed marine sediments collected during the IODP Expedition 379. The sediments recovered from the Site U1532 on the Amundsen Sea continental rise act as a historical archive, recording changes in ice sheets and ocean conditions over millions of years.

They identified two distinct sediment layers reflecting alternating cold and warm climate phases: thick, gray, and finely laminated clays from cold glacial periods, when ice extended across much of the continental shelf; and thinner, greenish layers formed during warmer interglacial periods. The green color comes from the microscopic algae, indicating open, ice-free ocean waters. Crucially, these warm-period layers also contain iceberg-rafted debris (IRD), small rock fragments carried by icebergs, that broke off from the Antarctic continent. As these icebergs drifted across the Amundsen Sea and melted, they released this debris onto the seafloor.

The team identified 14 prominent IRD-rich intervals between 4.65 and 3.33 million years ago, each interpreted as a major melt event when the WAIS partially retreated.

To determine how far inland the ice had retreated, the researchers analyzed the chemical “fingerprints” of the sediments. They measured isotopes of strontium, neodymium, and lead, which vary depending on the age and type of the source rock. By comparing these signatures with those of modern seafloor sediments and bedrock samples from across West Antarctica, the team traced much of the debris to the continental interior, particularly the Ellsworth-Whitmore Mountains.

The sediment record reveals a consistent four-stage cycle of warming and cooling. During cold glacial periods, the ice sheet was extensive and stable, covering the continent. As the climate warmed, during the early interglacial stage, basal melting began, leading to the inland retreat of the ice sheet. At peak warmth, during the peak interglacial stage, large icebergs calved from the retreating ice margin and transported sediment from the Antarctic interior across the Amundsen Sea. As temperatures cooled again, during the glacial-onset stage, the ice sheet rapidly regrew, pushing previously deposited sediments toward the shelf edge and transporting them further downslope into deeper waters.

“Our data and model results suggest that the Amundsen Sea sector of the WAIS persisted on the shelf throughout the Pliocene, punctuated by episodic but rapid retreat into the Byrd Subglacial Basin or farther inland, rather than undergoing permanent collapse,” says Prof. Horikawa

The findings indicate that the WAIS has undergone retreats far beyond its current extent, underscoring its extreme vulnerability to future warming and its potential to drive substantial sea-level rise.

 

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Reference
DOI: 10.1073/pnas.2508341122      

 

About University of Toyama, Japan
University of Toyama is a leading national university located in Toyama Prefecture, Japan, with campuses in Toyama City and Takaoka City. Formed in 2005 through the integration of three former national institutions, the university brings together a broad spectrum of disciplines across its 9 undergraduate schools, 8 graduate schools, and a range of specialized institutes. With more than 9,000 students, including a growing international cohort, the university is dedicated to high-quality education, cutting-edge research, and meaningful social contribution. Guided by the mission to cultivate individuals with creativity, ethical awareness, and a strong sense of purpose, the University of Toyama fosters learning that integrates the humanities, social sciences, natural sciences, and life sciences. The university emphasizes a global standard of education while remaining deeply engaged with the local community.

Website: https://www.u-toyama.ac.jp/en/

About Professor Keiji Horikawa from the University of Toyama, Japan
Keiji Horikawa is a Professor in the Faculty of Science at the University of Toyama, Japan, and a geochemist specializing in paleoceanography and paleoclimate research. His work focuses on reconstructing past climate and ocean conditions through geochemical analyses of marine sediment cores. He participated in the International Ocean Discovery Program Expedition 379 to the Amundsen Sea in 2019 and studies the response of the West Antarctic Ice Sheet to warm Pliocene climates. He heads the Horikawa Lab for Paleoceanography and Geochemistry, which aims to improve understanding of Earth’s climate system.

 

Funding information
This work was supported by JSPS KAKENHI Grant Numbers JP21H04924 and JP25H01181 and JP21H03590, JP23K21746, and JP25K03252 and was conducted by the support of Joint Research Grant for the Environmental Isotope Study of Research Institute for Humanity and Nature, and partly carried out under the Joint Research Program of the Institute of Low Temperature Science, Hokkaido University (23G056).

C. Siddoway’s contributions were supported by U.S. NSF awards 1917176 and 1939146 was funded through the Natural Environment Research Council (NERC) UK IODP grant NE/T010975/1. E.A. Cowan was supported by a postexpedition award from the U.S. Science Support Program of IODP.

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Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2508341122 

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

Repeated major inland retreat of Thwaites and Pine Island glaciers (West Antarctica) during the Pliocene

Article Publication Date

6-Jan-2026

Ancient Antarctica reveals a 'one–two punch' behind ice sheet collapse

Binghamton University

When we think of global warming, what first comes to mind is the air: crushing heatwaves that are felt rather than seen, except through the haziness of humid air. But when it comes to melting ice sheets, rising ocean temperatures may play more of a role — with the worst effects experienced on the other side of the globe.

A new paper in Nature Geoscience, “Spatially variable response of Antarctica’s ice sheets to orbital forcing during the Pliocene,” explores the complicated dynamics.

While Binghamton University Associate Professor of Earth Sciences Molly Patterson is the first author, the 43 co-authors include several Binghamton alumni, such as Christiana Rosenberg, MS ’20; Harold Jones ’18; and William Arnuk, PhD ’24. The study’s results directly address one of the main goals of the International Ocean Drilling Program (IODP) Expedition 374: to identify the sensitivity of the Antarctic ice sheet to Earth’s orbital configuration under a variety of climate boundary conditions. Because of this, all shipboard science team members are included as co-authors because of their contributions to the data sets used in the article, Patterson explained.

Their research considers the Antarctic ice sheet during the Late Pliocene period, from 3.3 to 2.6 million years ago. From 3.2 to 2.8 million years ago, the global average temperatures were around 2 to 3° Celsius higher than pre-industrial values, in line with the “middle of the road” scenario for climate change, in which temperatures are expected to rise around 2.7°C by 2100.

“Thus, Pliocene records are considered to be useful analogues for understanding what a future with this level of warming might be like,” Patterson explained.

Climate forcing refers to any external factor that causes a change in Earth’s energy balance —incoming versus outgoing heat — and ultimately leads to warming or cooling in the Earth system.

Non-human factors that can affect this energy balance include tectonic changes, volcanic eruptions and shifts in the sun’s energy output, such as sunspot cycles that happen every 11 years. Another factor is “orbital forcing,” or changes in Earth’s orbit around the sun; this has typically driven glacial and interglacial cycles, which have lasted around 100,000 years — at least for the last 800,000 years or so.

The non-human factors that affect the Earth’s climate occur on different time scales, Patterson said.

“Here we are using geological archives to test how these important components of the climate system respond naturally to warmer climates,” she said.

Antarctica is primarily divided into two sectors: West Antarctica, where the ice sheet sits in the ocean, and East Antarctica, where the ice sheet primarily sits on land. During the warm periods of the Pliocene, large parts of West Antarctica and some low-lying areas of East Antarctica experienced significant ice-melt, contributing to a 3- to 10-foot rise in global sea levels.

One of the study’s main conclusions: Under warming conditions similar to the Pliocene, the part of West Antarctica located adjacent to the Pacific Ocean will see its ice disappear at a faster rate. Over the long term, however, both oceanic and atmospheric warming will contribute to rising global sea levels.

You can think of it as an equation of sorts: A warmer climate leads to less sea ice around Antarctica, which then causes the ocean to heat up. Due to the warmer water, the parts of the ice sheet sitting on the ocean melt first. Over time, as the climate continues to warm, the ice sitting on land will also retreat.

“In other words, it’s a one–two punch on the system with a consequence of raising sea levels globally,” Patterson said.

What you may not realize: Because of gravitational effects similar to ocean tides, the loss of ice in the Southern Hemisphere actually has a greater impact on coastlines in the Northern Hemisphere. Conversely, when ice sheets lose mass in the Northern Hemisphere, Southern Hemisphere coastlines are affected more.

With that in mind, New York would be more affected by a 7-meter rise in sea levels from the loss of Antarctic ice than a similar rise from melting ice sheets in Greenland, Patterson pointed out.

Geological archives and modeling experiments provide the long-term context needed to evaluate current changes and help scientists identify the mechanisms that drive the climate system. Ultimately, this research may help us formulate more accurate predictions about our climate change future.

“Basically, geological archives serve as a vital tool for testing the accuracy of climate models used to project future scenarios,” Patterson said.

About Binghamton University

Binghamton University, State University of New York, is the #1 public university in New York and a top-100 institution nationally. Founded in 1946, Binghamton combines a liberal arts foundation with professional and graduate programs, offering more than 130 academic undergraduate majors, minors, certificates, concentrations, emphases, tracks and specializations, plus more than 90 master's, 40 doctoral and 50 graduate certificate programs. The University is home to nearly 18,000 students and more than 150,000 alumni worldwide. Binghamton's commitment to academic excellence, innovative research, and student success has earned it recognition as a Public Ivy and one of the best values in American higher education.

 

NUS Medicine takes on global, publicly accessible platform to strengthen data and insights for women’s health

National University of Singapore, Yong Loo Lin School of Medicine

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Women continue to experience a significant health gap, typically influenced by access to treatment, effectiveness of treatment and available resources dedicated to understanding health conditions, with wide-ranging human and economic implications. To contribute in narrowing the women’s health gap, the Global Centre for Asian Women’s Health (GloW), under the Yong Loo Lin School of Medicine, National University of Singapore (NUS Medicine) will take over the hosting and enhancement of the Women’s Health Impact Tracking (WHIT) platform, a first‑of‑its‑kind, publicly accessible tool which measures progress on closing the women’s health gap across a set of conditions and countries.

 

The WHIT platform—initiated and developed by the World Economic Forum (WEF), in collaboration with the McKinsey Health Institute (MHI)—consolidates and translates complex datasets into clear, comparative insights. It supports decision-making across clinical and public health agencies, research institutions, advocacy groups, and funding bodies. Highlighting conditions that uniquely or predominantly affect women, it identifies where needs are greatest and where care delivery, clinical effectiveness, or data quality require closer attention. By comparing disease burden with current investment patterns, WHIT helps to identify under-resourced areas. It complements major datasets such as the Global Burden of Disease (GBD) and WHO mortality data, offering a consolidated view of gaps and opportunities at global and national levels.

 

Research by the WEF and MHI indicates that closing the women’s health gap could yield substantial benefits, including improvements in quality of life and productivity. Earlier analyses estimate that narrowing the gap could add up to US$1 trillion to the global economy annually by 2040[1]. These findings underpin The Blueprint to Close the Women’s Health Gap, which outlines the global actions needed to advance women’s health—and which provides the foundation for the creation of WHIT, as a tool to measure progress against this agenda.

Professor Chong Yap Seng, Lien Ying Chow Professor in Medicine, and Dean of NUS Medicine, said, “As stewards for the WHIT platform, NUS Medicine will build on its already strong foundations so that the platform can serve as a high quality, long-term resource for policymakers, clinicians, researchers, and the public. Advancing women’s health requires coordinated, international effort—to ensure that the issues affecting women are measured consistently and understood more clearly.”

 

Moving forward, WHIT will further broaden its condition coverage, improve data quality, strengthen participation from countries—particularly low- and middle-income regions—and deepen use cases for stakeholders across disciplines. The aim is to establish a comprehensive and long-term data/information platform that enhances accountability and supports coordinated action on major health conditions among women. It will continue to support leaders across sectors in building a future where women’s health is understood, prioritised, and improved worldwide.

 

Professor Cuilin Zhang, Director of GloW, NUS Medicine, said, “Improving women’s health requires sustained attention to the conditions that affect us most, risk factors that lead to the conditions, effective methods that treat the conditions, and factors that shape our access to screening, diagnosis, and care. WHIT brings these issues into focus by organising information and data in a way that is accessible, understandable, transparent, and actionable. We aim to extend its reach so that countries and partners can make better-informed decisions to support women’s health across diverse landscapes. Maintaining and lifting the platform would require tremendous, joint efforts from multiple disciplines in our ecosystem—involving epidemiologists, clinicians, data scientists, economists, and more. We welcome partners and collaborators.”

 

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[1] https://www3.weforum.org/docs/WEF_Closing_the_Women’s_Health_Gap_2024.pdf

 

The rising risk of flooding and the role of nature-based solutions

University of Vermont

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For decades, flooding has remained one of the most destructive and deadly natural disasters in the United States, causing an average of $8 billion in damages and nearly 90 deaths each year.

With climate change intensifying storms and urban development replacing natural flood barriers, both the frequency and severity of flood events are on the rise.

Warming temperatures allow the atmosphere to hold more moisture, fueling heavier rainfall. At the same time, as cities grow, natural landscapes are being replaced with concrete and asphalt, increasing runoff and overwhelming stormwater systems. 

As a result, flood risks are rising nationwide, including in states that have not historically faced frequent flooding. By 2100, the number of Americans exposed to flooding could nearly double.

Investing in Natural Spaces

Nature-based solutions (NbS), such as restoring wetlands and reconnecting floodplains, can significantly reduce flood impacts by slowing and absorbing runoff. Unlike dams and levees, these approaches also deliver added benefits, including improved air quality, carbon storage, biodiversity, and aesthetic and recreational value. Despite these advantages, NbS remain underused.

University of Vermont researchers supported by the Cooperative Institute for Research to Operations in Hydrology probed public perception and attitudes on flood mitigation through a nationally representative study. The study published in the journal, People and Nature, reveals that while many people recognize the value of engineered structures, interest is growing in natural alternatives, specifically when their additional benefits are realized. 

Public Awareness and Support

Numerous obstacles need to be overcome to enhance the usage of NbS for addressing flood risk, including technological, financial, political, and social barriers. 

Currently, public knowledge remains limited. 

“Only about half of respondents knew that wetlands reduce flood risk, and many were unfamiliar with basic flood terminology. Less familiar terms like ‘flood stage’ and ‘areal flood’ caused widespread confusion,” notes Dr. Jessica Balerna, a University of Vermont post-doctoral scholar who led the publication of these results. 

This lack of knowledge contributes to uncertainty and resistance toward unfamiliar solutions, as well as misinterpretation of flood warning messages.

Investment Preferences

When asked about how municipalities should use public funds to mitigate floods, most respondents preferred a balanced approach, with a 50/50 investment between natural and engineered solutions. Balerna said that shows people are not necessarily opposed to natural solutions, but they are more comfortable when they are paired with traditional infrastructure.

Brendan Fisher, professor in the Rubenstein School and co-lead on the project, said “there is not much work comparing the full costs and benefits of nature-based solutions and hard infrastructure approaches to flood mitigation. There are going to be places in the landscape where one option is going to make much more sense than the other. Natural solutions offer a suite of co-benefits to people and biodiversity when preferred, but our work here shows that the average citizen isn’t that familiar with just how, and how much, natural solutions can benefit them."

Today, most communities across the United States rely solely on grey infrastructure solutions, like dams and levees, for flood mitigation. With more than 90,000 dams across the nation, and most of them over 60 years old, engineered solutions have long dominated the public’s perception in terms of flood control.

Those with less flood experience or who live outside flood-prone areas tended to favor engineered structures, reflecting the influence of familiarity.

Shaping Support for Nature-Based Solutions

Support for nature-based approaches among those surveyed in the study was strongest among people with higher education, greater flood literacy, and awareness of their local flood risk.

Those who were more knowledgeable about the benefit of natural spaces wanted to see more investment of government and tax-payer dollars into these spaces, even at the expense of engineered structures.

The more benefits participants recognized, the more likely they were to favor public investment in interventions such as restoring wetlands and implementing riparian forest buffers.

Political identity also played a role: liberals and moderates were more supportive of NbS than conservatives, likely due to associations with climate change policy. This highlights the need to frame environmentally-oriented interventions for flood mitigation around local, practical benefits rather than national political narratives. 

Closing the Gap

The study underscores that education and local engagement are key to expanding support for nature-based flood solutions. Clear communication about flood risks and the economic, recreational, and community benefits of NbS can build trust and reduce political resistance. Community-focused planning and transparent decision-making can help normalize these approaches.

As flooding becomes more widespread and unpredictable, proactive engagement and investment are critical. By improving flood literacy and highlighting how working with nature enhances resilience, communities can adopt more effective, sustainable strategies to protect lives and property.

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Journal

People and Nature

DOI

10.1002/pan3.70229 

Method of Research

Survey

Article Title

Survey-based study of public perceptions and preferences for mitigating flood risk via nature-based solutions in the United States

Article Publication Date

7-Jan-2026