Did you know that marine ecosystems provide vital functions, such as producing oxygen and storing excess heat and CO₂? Climate change is increasingly affecting our ocean, including the North Sea, and its ability to function properly.
UNRIC interviewed Jan Seys, a Belgian marine biologist and spokesperson for the Flanders Marine Institute (VLIZ) in Ostend, Belgium, to learn more about the impact of climate change on the North Sea and what we can do to counter it.
Why is the North Sea important for countering climate change?
The North Sea, like all ocean basins, functions as a climate regulator. Globally, the ocean absorbs 25% of the CO₂ emitted by human activity and, more importantly, 90% of the excess heat. In other words, 90% of the additional heat that radiates into our atmosphere is taken up by our oceans. Without it, human life would no longer be possible.
The North Sea is a tiny, yet biologically rich and extensively studied region of the global ocean. As such, it offers valuable opportunities for scientific learning. Its shallow nature, an average depth of 90 metres, which is less than the height of the tallest building in Ostend, combined with significant input from surrounding estuaries, makes the area highly productive. It is bordered by a densely populated region and benefits from a strong concentration of knowledge, expertise, universities, and specialised institutes.
What are the main consequences of climate change on the Belgian North Sea?
The impact is substantial. Over the past 60 years, the temperature has increased by approximately 2 °C, which is significant and comparatively fast when measured against other regions of the world.
Sea level has risen by about 20 centimetres in the last 50 years, a change roughly in line with the global average. In response, the Flemish government launched the Coastal Safety Master Plan in 2011, a programme aimed at protecting us against flooding by raising and widening beaches and by building a storm surge barrier in the mouth of the river Yser, among other measures.
Another phenomenon is marine heat waves. Their frequency and intensity are increasing because of global warming. Marine heat waves occur when the sea temperature remains unusually high for more than five consecutive days and exceeds the level commonly observed 90% of the time. These heat waves can therefore also take place during winter.
What is the impact of marine heat waves on ecosystems and marine life?
Marine heat waves have a vast impact on ecosystems and species, leading to tropicalisation, the migration of species to colder regions as their current habitats become too warm.
Atlantic cod is one example from the North Sea, but other species, such as plankton, are also affected. Small copepods, a particular type of plankton, have shifted 1000 kilometres northward. This type of plankton constitutes the primary food source for Atlantic cod larvae.
Another example is the lesser weever. Compared to last year, its presence has increased sevenfold. It is considered the most dangerous animal in the Belgian part of the North Sea due to its poisonous spines.
Research from other studies shows that two out of three fish species in the North Sea have shifted between 50 and 500 kilometres northward, contributing to tropicalisation. On the other hand, various animal and plant species that would typically not be present in this region because it was too cold are now able to survive much more easily in the North Sea when temperatures are higher.
In addition, there is a notable shift in the phenology of plankton and zooplankton. These organisms are altering their behaviour, which is impacting the entire ecosystem. Since plankton form the base of the food chain, any change at this level affects all species that depend on them.
These examples illustrate how marine life is changing, from a predominantly cold-water fauna to a warmer-water fauna that now includes species such as anchovy, sardines and an increasing number of cuttlefish. This shift has a cascading effect throughout the ecosystem.
How have CO₂ levels changed globally in 2025?
Although the rise in CO₂ emissions seems to be slowing to some extent, CO₂ levels in the atmosphere continue to increase, leading to significant consequences for the Earth’s temperature.
The main worry among scientists is exceeding a temperature rise of 2 °C, as the potential impacts beyond this point are unknown. Above that threshold, various feedback mechanisms are triggered, accelerating global warming and intensifying its adverse effects.
One of those tipping points is if temperatures rise sufficiently to cause permafrost thawing, particularly in Russia. In that case, vast amounts of methane could be released. Methane is forty times more potent as a greenhouse gas than CO₂. Once such a release occurs, it cannot be stopped.
It is the combination of several feedback loops and tipping points that causes concern among scientists. Do you want to live in a world where even scientists do not know what will happen? No. So, there is a very good reason for keeping the global temperature rise below 2 °C. Achieving this target remains possible, but it will be challenging.
Scientists are also concerned about ocean acidification due to rising CO₂ levels in the atmosphere. As the ocean becomes more acidic, it becomes increasingly difficult for various organisms, such as oysters, mussels, coral, certain plankton species and cuttlefish, to form their calcium-based skeletons. Half of the biodiversity in the ocean might be affected. The world’s oceans have already been acidified by 30%.
Changes in our ocean system also impact oxygen levels, which have already decreased by 2% globally, as well as sea level rise, flooding, fishing, and other related issues.
How can scientists and citizens counter the impact of climate change on the Belgian North Sea?
First and foremost, it is of course up to each of us to develop more climate-friendly behaviour. But there is more.
The ocean is vast, and scientists cannot tackle its challenges alone. To address this, VLIZ has established several monitoring initiatives known as “citizen science“, which aim to actively involve members of the public. In these programmes, scientific research is carried out by citizens themselves, creating a more effective connection between society and science. In Belgium, we currently run four such programmes, enabling the development of long-term data sets which are crucial for developing models that help us better understand the ocean.
Citizens contribute valuable data and gain firsthand insight into the effects of climate change. As a result, public awareness of environmental issues has significantly increased. If you can join forces and do it together, everybody wins.
In this context, VLIZ is participating in a European project called Marine Citizen Science Data Horizon, CS-MACH1. This project brings together individuals engaged in marine citizen science across Europe to establish a more efficient flow of data, making it accessible and useful for policymakers.
Ultimately, behavioural change is essential for every individual. In my 25 years of working on ocean-related issues, this is the first time we have frameworks that genuinely call upon the world to do something about the sustainability of the ocean: the UN Ocean Decade, launched in 2021, the first designated decade for the ocean, and the EU Mission: Restore Our Ocean and Waters. These initiatives help to create the behavioural change that is needed.
Citizens are becoming increasingly ‘ocean literate’ and start to understand that the ocean is a vital and central component of the entire system. This understanding is fundamental to how we will address climate change.