Our planet relies on the oceans as climate regulators. At the same time, the effects of our emissions are most evident in the oceans. Today, eutrophication, climate change, ocean acidification, and invasive species are some of the challenges the oceans face. The Ocean – A key player in climate
The oceans are already significantly impacted by human activity, making them sensitive to further influence from climate change. Habitats of species may disappear, shift, or shrink, while others gain access to new distribution areas. This can lead to a reduction in biodiversity, exacerbating the oceans’ resilience against, for example, climate change.
According to the International Panel on Climate Change (IPCC), over 90 percent of excess heat and between 20 and 30 percent of carbon dioxide emissions have been absorbed by the oceans. Carbon dioxide is absorbed by the oceans as the gas dissolves in water, and phytoplankton in surface waters take it up and bind it in organic material through photosynthesis. Phytoplankton are then consumed by zooplankton, which, along with other organisms, fall towards the ocean floor as marine snow when they die. This process allows large amounts of carbon from the upper layers of the ocean to reach deeper layers which is crucial for the organisms there. The transport of carbon to the bottom also ensures that it remains in the oceans much longer than if it were to stay in the surface layer, potentially leaking carbon dioxide back into the atmosphere.
One effect of increased emissions of greenhouse gases is ocean warming. When the oceans become warmer, the entire ecosystem is affected. Fish size may change, algal blooms and dead zones increase, and many species such as eelgrass, harbor seals, and mussels struggle to survive. Furthermore, as water becomes warmer, it becomes more challenging for the oceans to absorb carbon dioxide, potentially worsening climate change further.
The warming of the oceans is now the fastest in at least 11,000 years. Although it can be slowed down with powerful measures, the stored heat energy contributed so far will continue to warm our planet for hundreds or even thousands of years.
The oceans play a large role in how we experience the climate on our planet. Thanks to the Gulf Stream, Nordic countries for instance have a relatively mild climate in relation to their northern positions. Warming of the seawater leads to significant changes in ocean circulation and rising sea levels as the ice in the ocean’s melts. The decrease in ice is more pronounced in the northern hemisphere than in Antarctica, and research indicates that the ice will continue to melt for at least 100 years, regardless of the measures taken. However, the effects worsen with the more greenhouse gases we emit. Many scientists are concerned about how the Earth will be affected when the Arctic ice disappears, as it affects the climate by reflecting solar radiation.
Climate change will affect the salinity of the oceans. In areas near the equator, evaporation will increase, leading to an increase in salinity. In areas closer to the poles, such as the Swedish seas, salinity will decrease as precipitation and the influx of freshwater increase and polar ice melts.
Changes in salinity and temperature can, among other things, lead to increased oxygen deficiency. This is because the stratification of seawater in depth becomes clearer, preventing mixing and transport of oxygen-rich water to the bottom. Salinity and temperature also largely control the geographic distribution of species, meaning that climate change can have significant consequences for biodiversity.
The absorption of carbon dioxide by the oceans has almost doubled since the 1980s, but it has come at a cost. When carbon dioxide is mixed into the water column, the chemistry of the ocean changes. A higher concentration of carbon dioxide in the ocean increases acidity, a phenomenon called ocean acidification, sometimes referred to as the “evil twin of warming.” Like the effects of climate change, ocean acidification can lead to the extinction of species or shifts in ecosystems. Studies show that key species such as brittle stars in Gullmarsfjorden would not survive the acidification expected within a few decades. And since many species depend on them, it can have significant consequences for the entire ecosystem.
Ocean acidification affects various biological processes such as photosynthesis and calcification. Many marine organisms are affected by the fact that ocean acidification makes calcium less accessible, as they form shells and skeletons from calcium. Corals are affected by both calcium deficiency and increasing temperature. Coral reefs are one of the ecosystems with the highest biodiversity globally but are also most affected by climate change, leading to coral bleaching. Even the coral Lophelia in Kosterhavet National Park is affected by increased temperature and acidity.
Today, several marine areas, such as the Black Sea and the Baltic Sea, are affected by eutrophication. This is due to increased nutrient input, leading to the proliferation of fast-growing phytoplankton, cyanobacteria, and filamentous algae. This makes it difficult for other species to survive as much sunlight is blocked. When the algae sink to the bottom, bacteria use up the oxygen to break down the organic material. This has resulted in large dead zones in, for example, the Baltic Sea, where only bacteria and a few other microorganisms can survive in the oxygen-depleted environment. Eutrophication leads to overgrown bays, deteriorated water quality, and reduced biodiversity.
While some nutrient inputs occur naturally, human activities contribute significantly by adding extra nutrients in the form of nitrogen and phosphorus. Agriculture, sewage, industries, forestry, road traffic, and shipping all contribute to eutrophication. Because eutrophication in the Baltic Sea has been ongoing for so long, there are old sins in the form of nutrients bound in sediment. Internal loading is a process where these nutrients are released, mainly when there is limited oxygen at the bottom. Eutrophication thus creates a negative spiral where the system eventually feeds itself.
Although the eutrophication status is still poor in most parts of the Baltic Sea, improvements can be seen in the Gulf of Finland, Kattegat, and the Belts. According to the Helsinki Convention, HELCOM, nitrogen inputs have decreased by 19 percent, and phosphorus by 24 percent since the mid-1990s. To further reduce the impact of eutrophication, the main sources, namely agriculture and wastewater, should be controlled.
Many environmental toxins have decreased significantly since the 1970s. However, society’s extensive use of chemicals needs further reduction. History speaks clearly: actions make a difference.
Almost all toxic substances released into nature are considered environmental toxins. Some of these can harm animal and plant life even at low levels if they persist for an extended period. Environmental toxins often break down slowly, meaning their effects can be both long-lasting and spread over large areas. Some common environmental toxins include mercury, lead, cadmium, tributyltin (TBT), DDT, PCB, and dioxins.
Most organic environmental toxins are fat-soluble and therefore accumulate in the fat tissue of various organisms. Toxins accumulate to a greater extent the higher up the food chain you go. Therefore, top predators, often suffer more from environmental toxins than prey animals. When humans eat fish that have stored environmental toxins, they ingest these toxins. This has led to specific dietary recommendations for pregnant women, children, and young people when it comes to fatty fish.
White-tailed eagles and seals were heavily affected by environmental toxins during the 1960s and 70s because they are long-lived animals high up in the food chain. The white-tailed eagle was close to extinction because the chicks did not survive. Seals in the Baltic Sea struggled to reproduce, and in combination with hunting, environmental toxins led to only a few thousand seals remaining. After measures were taken to reduce the levels of environmental toxins, white-tailed eagles and seals in Sweden increased.
But despite the prohibition of PCB and many measures aiming at reducing the spread of environmental toxins, the levels are still relatively high. Some dioxins are considered some of the most dangerous environmental toxins as they can affect the development of our brain, immune system, nervous system, and the ability to have children. This is due to their long-lasting nature and the existence of emission sources that Baltic Sea countries have not yet addressed. Additionally, humans constantly introduce new chemicals that risk reaching the oceans.
A common pollution in the oceans today is plastic. In the oceans, more than around 150 million tons of plastic float, increasing by 5 to 13 million tons each year. Estimates show that 80–85 percent of marine litter in the EU consists of plastic. Of this, 50 percent are single-use products, and 27 percent are fishing-related items. Lost fishing gear, such as nylon nets, often float around as death traps for animals, known as ghost nets. Whales, seals, seabirds, and other animals can get entangled in these and die.
To try to reduce the problems of plastic waste in the oceans, the EU introduced a directive against single-use plastics in 2021, prohibiting the sale of plastic straws, among other items. Since it takes several hundred years for plastic to break down in the ocean, it instead slowly disintegrates into smaller parts, eventually becoming microplastics. Microplastics are also flushed into the oceans from wastewater treatment plants, often originating from fabrics made of synthetic materials and additives in hygiene products and cosmetics. About 10–30 percent of plastic particles elude capture by wastewater treatment plants and end up in the oceans. If animals ingest microplastics, they can be harmed or poisoned. Additionally, when they consume plastic, a false sense of being full occurs, leading to malnutrition. In water, plastic particles act as magnets for bacteria and environmental toxins, which animals ingest.
Although no significant risks for the environment and health have been found with current concentrations of plastics, knowledge gaps are significant. This currently prevents any conclusive statements about the risks of microplastics.
TEXT: Lina Mattsson
A new report by the country's intelligence chiefs states that the nation's security is threatened by the climate crisis, something that the Guardian was the first to report on. And the threat, they say, is much closer in time than we realise.
Arctic seals are threatened with extinction, mainly due to climate change and human activity, according to an updated list from the International Union for Conservation of Nature (IUCN).
Greenhouse gas emissions have made the oceans increasingly acidic. Now, according to a new report, ocean acidification has exceeded the limit considered safe for marine life for the first time. ‘The consequences could be really serious,’ says Albert Norström, associate professor at the Stockholm Resilience Centre.
The government wants to remove the Environmental Code's ban on nuclear power in virtually all Swedish archipelagos. This would open the way for nuclear power plants in Bohuslän, Öland, Gotland, and the Stockholm archipelago, among other places.
Antarctica has been relatively unaffected by climate change. However, according to a recent study, the situation on the continent is beginning to resemble that of Greenland.
For the people of the Pacific Islands, the sea is life, it provides most of their food, it regulates their climate. It’s a familiar friend, but for these low-lying island nations, rising seas are now threatening their very existence. Ironically, this threat has its origins far away, where emissions from industries that have enriched the world's most powerful industrial nations are the biggest contributors to the changes that make Elson Kelen, a community leader on Majuro, the capital of the Marshall Islands, fear for the future of his children and grandchildren.
Indigenous lawyer Julian Aguon from the Pacific island of Guam and the student organisation Pacific Islands Students Fighting Climate Change (PISFCC) have been awarded the 2025 Right Livelihood Award, also known as the Alternative Nobel Prize.
All parts of the oceans are under triple attack, according to the EU's Copernicus Climate Service's major annual ocean report. ‘These changes affect us all – ecosystems, society and the economy,’ says oceanographer Karina von Schuckmann.
In June 2025, Coral reef researchers, Sylvia Jageroos and Didier Zoccola dived the coral reefs of the Bikini Atoll, observing the coral reef ecosystems, identifying corals and collecting samples. Close on 80 years after American nuclear tests devastated the Atoll, they discovered a surprisingly resilient and healthy ecosystem and will now be able to further analyse their findings to determine whether they have found coral species that are unusually resistant to the effects of climate change. Nästan 80 år efter att amerikanska kärnvapenprov ödelade atollen är det ett överraskande motståndskraftigt och friskt ekosystem de hittar. Tillbaka i labbet ska de analysera fynden för att se om de har hittat korallarter som är ovanligt motståndskraftiga mot klimatförändringarnas effekter.
Seven of the nine so-called planetary boundaries have now been exceeded. The latest is ocean acidification, which, according to a new report, has passed the limit of what is safe for marine life. And life in the sea is already feeling the effects.
One of the world's most common organisms is threatened by rising sea temperatures. The amount of the most common type of cyanobacteria (prochlorococcus) is at risk of being halved unless climate change is slowed down.
The Swedish National Audit Office has now released a report criticizing the government's efforts to meet the sustainability goals set out in Agenda 2030. The Ministry of Climate and Business does not wish to comment on the Swedish National Audit Office's review at this time.
What will you remember from the inauguration of a national park in your own neighbourhood? A sunny autumn day? Absolutely. Some more or less pertinent phrases from your Minister of Climate and the Environment? Maybe, but mostly the fact that she wasn’t even born when the park was first discussed. A trumpeter and two slightly wayward sheep? Yes, the unexpected will always stick to your memory.
Even the ancient Greeks held the yellow-striped mullus – or, in short, the mullus – in high regard. With rising sea temperatures, it has been appearing on the Swedish west coast in autumn for several years now. However, spawning and reproduction have never been recorded in Swedish waters. But there are many indications that the mullet can now be considered a resident and reproducing species. Many shallow bays along the west coast have been swarming with its fry this summer.
A year ago, almost all the inhabitants of the island of Gardí Sugdub in Panama left, following warnings that their homes would be swallowed up by the sea. All that remains is silence and a few people. ‘I will die here,’ says 62-year-old Luciana Pérez, who has chosen to stay.
There will be no agreement on global production, recycling and waste management of plastics. Negotiators are now leaving the meeting in Geneva empty-handed.
The Swedish name is St Pers fish, named after the apostle Peter and has a false eye to confuse predatory fish. In the Mediterranean, it is a popular food fish. But now it has arrived here in Sweden. At a depth of 20 meters in Gullmarsfjorden on the Swedish west coast, Deep Sea Reporter encountered a most ordinary and spectacular fish: the John Dory.
Sweden is praised for its waste management and its commitment to the development of the UN's global plastics agreement. At the same time, large amounts of plastic are leaking into Swedish waters. Experts warn that plastic emissions – where microplastics, overflow and sewage sludge all contribute to pollution – continue to threaten Swedish aquatic environments.
A species of Turbellaria completely new to Swedish waters has been discovered by divers along the Swedish west coast. It is large and dancing in nature and originates from more southerly latitudes. Deep Sea Reporter encountered the new worm at Flatholmen outside Lysekil.
Every year, a small group of harbour porpoises traverses a narrow strait from the Black Sea to the Sea of Asov, then returns again, in a natural migration cycle. Since prehistory, these Black Sea porpoises have been isolated, evolving separately from other porpoises, becoming smaller, but with larger snouts. They’re sleek and cute, with eyes and mouths that have the perpetual hint of a smile.
Every minute of every day, every week of every year, the equivalent of a garbage truck full of plastic is dumped into the sea. Every minute! And if we do nothing, this figure will only increase. According to estimates, if we do not stop plastic emissions, today's 11 million tonnes of plastic emissions per year will increase to 37 million tonnes by 2040.
The Great Barrier Reef in Australia has suffered the most extensive coral bleaching ever recorded, according to a government report.
This Pacific island nation could be completely flooded within 25 years due to rising sea levels. To address the threat of climate change, Tuvalu is now planning the world's first organized relocation of an entire nation.
Beaches in Australia are filled with dead sharks, stingrays, crabs, and squid. An unusually large toxic algae bloom is causing concern in the country as it lingers off the south coast, killing wildlife and destroying the fishing industry.
