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
When scientists study the Black Sea’s coastal seaweed forests, they often dive beneath the surface to see them in person. Formed by two species of brown algae in the genus Cystoseira, these ecosystems can look dull from a distance. “But when you actually dive deeper, you can see the biodiversity, and these various interesting invertebrates and fish species which are moving there,” says marine biologist Sofia Sadogurska.
The world has agreed on a climate agreement, but it resembles more a lowest common denominator agreement than a step forward. The most important thing seems to have been that the oil-producing countries avoided a provision on a ‘roadmap’ for phasing out fossil fuels. And the ocean – seems to have been completely forgotten.
Toxic bathing water, dead fish and dead seabeds – the impact of climate change on the sea is becoming increasingly clear. But the fight against marine death begins well inland. ‘2018 was a wake-up call,’ says the Swedish farmer Erika Olsson, one of many who have created wetlands.
In the Netherlands, barriers have been used for centuries to prevent the sea from engulfing the land. But another movement is asking whether the future is instead fluid – and experimenting with floating parks, farms and offices. ‘It's about living with the water,’ says Rutger de Graaf at Blue 21.
Vilasinee Klatalay hör till Moken-folket i Thailand. Tidigare bodde de i båtar på havet och flyttade mellan öarna. Men så ser det inte längre ut. 'When I was young, the water was clear and clean,' they say. 'There were lots of coral reefs and many different kinds of fish.' Today, they have stopped fishing and make a living by selling handicrafts made from plastic they have found in the sea, to tourists.
Andrea is a fourth-generation fisherman. The catch now is a lot lower because of the influx of tropical species brought about by warming temperatures. As he shows us the beautiful island of Burano, he also tells us about the drastic changes he has seen there. He urges that we must act now and together before it gets too late.
Earlier this year, the Great Australian Bight in southern Australia was hit by an algal bloom that lasted several months. The toxic algae killed sharks, crabs and octopuses, and spread very close to the world's largest sanctuary for whales. ‘This is an important warning sign,’ says Lily Miller-Lampard.
Angela Sondenaa belongs to the Siletz tribe in the American state of Oregon. After living in other places for many years, she has returned home and is now participating in a project to bring back the sea otters that have disappeared from the coast.
Bidyut tells the story about how the river has expanded by a third since he was a child. And the heavy rainfall he has seen lately is more than he has ever experienced before. He lives in the middle of Sundarban, a gigantic river delta that stretches across both sides of the Bangladeshi and Indian border. In recent years, the river has grown a third wider than when Bidyut was a child, and the rains are only getting heavier.
Pondang is a fisherman in Bajau Laut, located in Wakatobi National Park in Indonesia. Since he was born, he has had a strong connection to the sea.
He is a Sámi musician who is inspired by the Sea. But Climate change is causing the Sami to lose their language and is badly impacting their identity. This is a story about music, language and culture change due to climate change. ‘A lot has changed in just two generations,’ says Emil in the film.
The Melanesian Ocean Reserve is the first indigenous led, multi-national Ocean reserve on Earth. It is important, because it demonstrates that indigenous people can come up with initiatives to steward and guard and protect our planet. Edgar calls for action at this year’s COP.
Friday lives in Makoko a slum area right on top of the sea in Lagos, Nigeria. For the most part Friday is happy in his day-to-day life, but he has big dreams to educate everyone in Makoko about climate change. During rainy season, many houses flood and children fall into the water - but using good bamboo could stop this from happening.
Christopher Andersen and his diving buddies at Strömstad's sports diving club have found loads of the invasive sea squirt, also called ‘sea spit,’ in parts of the Koster Sea at the Swedish West coast, where they did surveys for the species just a year ago.
Nuala comes from Pernambuco in Brazil. She is a former professional surfer who runs a non-profit organisation that aims to democratise the sport while strengthening children's and women's connection to the sea.
Researchers at the University of Hawaii have studied how the marine ecosystem is affected in the Clarion–Clipperton Zone in the Pacific Ocean, where mining is currently being tested. The report shows that sediments stirred up by mining disrupt the food chain.
The seabed in Byfjorden on the Swedish West coast is completely dead below a depth of 15 metres. Limited water exchange, which means that oxygen is quickly consumed, combined with old sins from the Uddevalla shipyard, which has accumulated large amounts of heavy metals in the bottom sediments, has made life almost impossible down there. But a new project is bringing life back to the dead seabed.
The new report from the United Nations Environment Programme, Emissions Gap Report, states that the world has so far failed to slow down climate change sufficiently. For the ocean, this means dying corals, migrating species and even higher temperatures. - Cod may abandon the North Sea and the Baltic Sea altogether, says Kerstin Johannesson, professor of marine ecology at the University of Gothenburg.
Catastrophic and life-threatening floods loom as Category 5 Hurricane Melissa reaches Jamaica. The storm is the strongest on the globe this year – and among the 20 strongest ever to form over the Atlantic.
They have been called a ‘secret weapon’ in the fight against climate change – eelgrass beds and kelp forests in the sea. They can be likened to trees in the sea that bind carbon dioxide 35 times faster than the Amazon rainforest. But they are under threat from human presence, environmental pollution and emissions.
Coral reefs have reached their limit. This is the conclusion of a new global report, which warns that most reefs will likely disappear unless powerful climate measures are taken. But in the midst of this crisis, there are places that show that recovery is possible—if nature is given a chance.
The world's largest environmental network, IUCN, has this week adopted motion 061 at its international nature conservation congress, calling on states to recognise ecocide, i.e. large-scale environmental destruction, as a serious crime under national and international law.
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).
