Photo by Randy Laybourne
The world’s oceans absorbed colossal amounts of heat in 2025, setting yet another record and fuelling more extreme weather, according to research published in Advances in Atmospheric Sciences. The additional 23 zettajoules absorbed represents approximately 37 years of global primary energy consumption, equivalent to more than 200 times the total electricity used by humans worldwide.
More than 90% of the heat trapped by humanity’s carbon pollution is taken up by the oceans, making ocean heat one of the starkest indicators of the relentless march of the climate crisis. Almost every year since the start of the millennium has set a new ocean heat record.
“Global warming is ocean warming,” said Prof John Abraham at the University of St Thomas in Minnesota. “If you want to know how much the Earth has warmed or how fast we will warm into the future, the answer is in the oceans.”
The study, compiled by more than 50 scientists from 31 institutions, found that approximately 33% of the global ocean area ranked among its historical top three warmest conditions. This extra heat makes hurricanes and typhoons more intense, causes heavier downpours and greater flooding, and results in longer marine heatwaves which decimate marine life.
Dr Kevin Trenberth, honorary academic at the University of Auckland, said: “The ocean is the hottest on record. We’re looking at creating a very different planet – do we really want to do that?”
UK develops first national marine heatwave strategy
UK scientists have developed the first coordinated national strategy to address marine heatwaves. A team led by the National Oceanography Centre has identified 40 priority questions that must urgently be answered to prepare for future risks and opportunities.
Marine heatwaves are periods of unusually warm sea temperatures, recognised as one of the fastest emerging climate-related drivers of ocean change. The unprecedented marine heatwave surrounding the UK and Ireland in summer 2023 exposed critical gaps in understanding.
Professor Sian Rees from the University of Plymouth stated: “Marine heatwaves are emerging as a serious and growing risk to the UK’s marine natural capital, with consequences that extend far beyond ecology. By altering habitats and species that underpin ecosystem services, these events threaten commercial fisheries, coastal livelihoods and the wider blue economy.”
The research, published in npj Ocean Sustainability, provides a roadmap for researchers, policy makers and funding bodies. Marine heatwaves can affect everything from plankton and fish stocks to coastal tourism, food security and mental health.
Dr Zoe Jacobs, lead author, stated: “Marine heatwaves represent one of the most urgent and least understood climate threats facing UK seas. Preparing for marine heatwaves is no longer optional, it is essential for ensuring a resilient ocean future.”
Japan confronts fishing culture upheaval
The impacts are particularly severe in Japan, where waters have heated at more than double the global average rate. Sea temperatures around Japan have risen by 1.33 degrees Celsius over the past century. Waters off eastern Tohoku have been about 6 degrees above preindustrial averages for the last two years.
The warming has triggered dramatic shifts in fish distribution. “Tachiuo (hairtail) used to be a distinctive fish characteristic of Osaka Bay, but their numbers have been decimated almost to nothing in the past three to four years,” local fisherman Ohama told The Japan Times. Hairtail is uniquely tied to Osaka’s fishing culture and regional cuisine.
Conversely, tropical species are expanding northward. Pufferfish catches in Fukuoka have decreased by about 30%, whilst Hokkaido now leads in landings.
Urgent action required
The North Atlantic and Mediterranean Sea are getting warmer, saltier, more acidic and less oxygenated, causing “a deep-reaching ocean state change, making the ocean ecosystems and the life they support more fragile.”
Abraham stated: “The biggest climate uncertainty is what humans decide to do. Together, we can reduce emissions and help safeguard a future climate where humans can thrive.”