What are Marine Heatwaves?
Marine heatwaves are periods of unusually high ocean temperatures that last for days, weeks or even months. They can stretch across vast areas of ocean and warm waters to depths of hundreds of metres.
These events are becoming more frequent, intense, and long-lasting due to climate change. Since 1982, the number of marine heatwaves has doubled. Recent examples have occurred in the North Atlantic, around Antarctica, and in the Mediterranean. Marine heatwaves disrupt ocean ecosystems, affect the global climate system, and have serious consequences for society, from damaged fisheries to extreme weather events.
What are the impacts of marine heatwaves?
The ocean supports the livelihoods of over three billion people and provides the main source of protein for one billion more. Marine heatwaves threaten this vital system in multiple ways:
Environmental impacts:
- Coral bleaching and reef loss
- Dieback of kelp and seagrass
- Disruption of fish populations
- Harmful algal blooms
- Mass mortality in invertebrate species
Societal impacts:
- Fisheries and aquaculture face economic losses worth billions globally
- Marine heatwaves can fuel stronger hurricanes and tropical cyclones
- They may drive heavy rainfall on land by increasing ocean evaporation
- Communities may face food insecurity and reduced marine resources
As the climate warms, these extreme events will become more common, making it vital to understand, monitor and predict them.
What causes marine heatwaves?
Marine heatwaves are caused by a range of ocean and atmospheric processes, acting alone or together. The main drivers are:
Surface heat flux.
Warming from the atmosphere, often under persistent high-pressure systems.
Ocean advection
Warm ocean currents carrying heat into a region.
Marine heatwaves caused by atmospheric heating are usually shallower and shorter. Those caused by ocean currents tend to last longer and extend deeper. Ocean mixing, how water layers interact and distribute heat, also affects the intensity and persistence of marine heatwaves.
Publications
A global assessment of marine heatwaves and their drivers
Nature Communications.
How is NOC researching marine heatwaves?
NOC scientists use long-term observations and advanced computer models to study the causes and consequences of marine heatwaves.
We combine satellite data, deep-sea observatories, robotic floats, and numerical models to monitor the ocean and simulate marine heatwave events, helping predict their impact and support adaptation.
Observing systems
- Satellites monitor daily sea surface temperatures across the globe
- Ships and fixed observatories collect measurements from the surface to the seafloor
- Autonomous instruments like Argo floats provide continuous data on ocean temperature and salinity
All observing systems show a clear trend: marine heatwaves are increasing in frequency, intensity and duration.
Modelling tools:
Our scientists develop high-resolution models that simulate marine heatwaves and forecast their future behaviour. These tools help researchers, industries and policy-makers make decisions that reduce vulnerability and support climate resilience.
Real world research impacts
Marine heatwaves affect people, economies, and ecosystems, from coral bleaching and biodiversity loss to severe weather and fisheries collapse. NOC research provides crucial insights to help manage and reduce these risks.
In summer 2023, sea temperatures around the UK were up to 5°C above average. NOC researchers helped analyse the causes, including sunny skies, calm seas and weak winds, and examined how the event raised land temperatures and rainfall.
NOC scientist Dr Zoe Jacobs mapped UK marine heatwave hotspots for the first time. The Southern North Sea and English Channel were identified as regions where heatwaves may be weaker but last longer, offering vital information for national adaptation planning.
Dr Jules Kajtar led a study in Tasmania, working with aquaculture stakeholders to assess risks and create a Marine Heatwave Hazard Index. Models suggest extreme marine heatwaves could occur there every 2-5 years by 2050.
Dr Zoe Jacobs co-led a UK-focused session at the 2024 Socio-Oceanography Workshop, identifying 40 priority research questions on marine heatwaves and their implications for society. A paper is currently under review.
Sharing our knowledge
NOC scientists work closely with national and international partners to share knowledge, raise awareness, and influence policy.
Want to learn more
Want to explore how scientists monitor, model, and respond to marine heatwaves and other extreme ocean events? Watch real-world examples and expert interviews in our free online course, Ocean Science in Action.