By Leon Barillet
Oceans on the Brink: A Global Reality Check
Starting this Monday, diplomats, scientists, and civil society leaders will converge in Nice, France for the 2025 United Nations Ocean Conference, under a stark theme “Accelerating action and mobilising all actors to conserve and sustainably use the ocean.” It comes not a moment too soon. From pole to equator, Earth’s oceans have long been exhibiting alarming signs of distress. Our plodding collective action towards protecting the oceans has only exacerbated their health. The planet’s blue lungs have absorbed over 90% of the excess heat trapped by greenhouse gases, fuelling record-breaking marine heatwaves. 2023 recorded global average sea surface temperatures surge to unprecedented highs, exceeding 19°C for the first time, with scientists coining the term “super-marine heatwaves” for these extreme events. The oceans have also taken up roughly a quarter of humanity’s CO₂ emissions, turning seawater more acidic — as much as 30% more acidic than pre-industrial levels. Meanwhile, global mean sea level has risen over 20 cm since 1900, a rate now accelerating as ice sheets melt and water warms. These shifts are already reshaping coastlines and imperilling marine life. “Many of the world’s marine ecosystems are suffering from the impacts of global heating, ocean acidification, overfishing and pollutants,” notes one ocean science expert, underscoring that the ocean biodiversity and climate crises are inextricably linked.
The health check only worsens from there. Chemical runoff and nutrient pollution are creating oxygen-starved “dead zones,” more than 400 of them now blot coastal waters worldwide, where fish and crustaceans can no longer survive. Plastic debris, perhaps the most visible blight, is inundating even the remotest seas. Every year, an estimated 11 million tonnes of plastic flow into the oceans, a number on track to double or triple by 2040 absent drastic action. Sunlight and waves break this deluge into trillions of microplastic particles, now found everywhere from polar ice to the Mariana Trench. In parts of the vast Pacific gyres, floating garbage patches span areas larger than France. The ocean, in short, is in a state of emergency, and the onus is on humanity to react and restore.
Warming Seas and Rising Stakes
Of all the threats, climate change looms largest over the oceans’ future. The latest science confirms that the ocean has been acting as a buffer, storing the vast majority of excess heat and about a quarter of emitted CO₂. This has spared us even more extreme atmospheric warming, but at a steep cost to ocean systems. Warmer waters are turbocharging tropical cyclones and driving fish to cooler ranges. They are also less able to hold oxygen, contributing to expanding hypoxic zones. The absorption of CO₂ causes carbonic acid to form, steadily lowering the ocean’s pH. Average surface pH has fallen by about 0.1 units since the mid-20th century, a 26% increase in acidity that is corrosive to shell-forming organisms and coral reefs. Today’s ocean chemistry changes are unprecedented in tens of millions of years, according to the UN’s climate panel, and they are reverberating through the marine food web.
Perhaps no symbols of climate impact are as evident as bleached coral reefs. Marine heatwaves have repeatedly driven corals to expel their symbiotic algae, turning reefs ghostly white. Unusually warm waters in recent years have caused mass bleaching events, threatening the foundation of reef ecosystems. In the past three decades alone, the world has lost a significant share of its living corals, by some estimates, half of all coral reef cover has vanished since 1950. Those that remain face an uncertain future, even if global warming is capped at 1.5–2°C, scientists project most reefs will suffer recurrent bleaching or worse. The loss of coral reefs, often called the “rainforests of the sea,” would rip away crucial habitat for countless species and strip coastal communities of natural storm protection and livelihoods.
Simultaneously, sea levels are inexorably rising as glaciers and ice sheets melt and warming ocean water expands. Current measurements indicate an accelerating rise of 3–4 millimetres per year, up from about 1–2 mm/year last century. Over the past century, seas climbed roughly 20–24 cm on average, already nibbling away at islands and lowlying coasts. Entire nations in the Pacific and Indian Ocean are grappling with saltwater intrusion and the prospect of displacement. Estimates indicate by 2100, under high-emission scenarios, global sea level could surge by a meter or more, a doomsday scenario for coral atolls and delta cities alike. Rising seas also further degrade wetlands and mangroves, natural buffers against storms, impairing the very ecosystems that could help us adapt. In essence, climateinduced warming, acidification and sea-level rise form a triple threat to ocean health, each reinforcing the other. The urgency of curtailing greenhouse emissions has become an ocean imperative as much as a climate one.
A Sea of Pollution: Plastics and Chemical Perils
Floating in parallel with climate stresses is a human-made plague of pollution that as well respects no borders. Plastic pollution, in particular, has garnered global attention as emblematic of humanity’s overspill. Since mass production took off in the mid-20th century, plastics have inundated the seas, persisting for hundreds of years. At least 17 million metric tons of plastic entered the ocean in 2021 alone. If trends continue, that flow could double or even triple by 2040, on top of an estimated 200 million tons already accumulating in the marine environment . From disposable shopping bags found in the deepest ocean trench to microplastics in plankton and whale guts, no corner of the ocean is untouched. The United Nations Environment Programme (UNEP) warns that plastic is now “the most harmful type of marine litter”, with ubiquitous debris choking wildlife and carrying toxic chemicals into food webs. Only about 9% of plastic waste is currently recycled; the vast majority ends up in landfills, incinerators, or, all too often, drifting out to sea.
Chemical pollutants compound the assault. Agricultural fertilisers running off into coastal waters trigger algal blooms that decay and consume oxygen, creating eutrophic dead zones devoid of marine life. Over 400 coastal dead zones have been identified worldwide, a number that has roughly doubled each decade since the 1960s, including a recurring hypoxic area in the Gulf of Mexico the size of New Jersey. Other contaminants like mercury, industrial chemicals, and oil spills further intoxicate marine food chains. Even remote Arctic seas show traces of our chemical footprint as currents and atmospheric winds carry pollutants poleward. The combined pollution load is not only a direct toxin to ocean species, but it also weakens ecosystems’ resilience to climate stress. Corals and oysters already strained by warmer, more acidic water are less able to cope when exposed to pollutants. Cleaning up this mess is a herculean task, but one the world is slowly starting to confront through global initiatives targeting plastics, waste management, and nutrient runoff.
Overfishing and Biodiversity in Freefall
Life beneath the waves is under assault not just from changing chemistry and pollution, but from intense overexploitation. The ocean’s bounty once seemed inexhaustible; today we know otherwise. According to the U.N. Food and Agriculture Organisation (FAO), over one-third of global fish stocks are overfished or depleted, a proportion that has more than tripled since the 1970s. In 1974, just 10% of monitored fish stocks were considered overexploited; as of 2020 that figure is about 35% and rising. Popular commercial species from Atlantic cod to Pacific bluefin tuna have seen populations crash from unsustainable harvest. Aggressive modern fleets, bycatch of non-target species, and illegal, unreported, and unregulated (IUU) fishing continue to undermine fisheries management in many regions. The tragedy of the commons is painfully evident on the high seas, where a lack of governance historically allowed a free-for-all on marine life beyond national waters.
The consequence is a precipitous decline in marine biodiversity. Iconic ocean creatures are now cornered into threatened status. A recent global assessment found that over one-third of all shark and ray species are at risk of extinction, primarily due to overfishing . Once-abundant ocean predators, from hammerhead sharks to manta rays, are dwindling, disrupting marine food webs that kept ecosystems in balance. Other groups from sea turtles to seabirds also face mounting pressures from fishing gear, habitat loss, and climate impacts. Coral reef ecosystems, home to an estimated 25% of marine species, have been hit by the twin scourges of warming and overfishing of key herbivores, allowing algae to overrun reefs. A school of reef sharks patrols a tropical ocean. Scientists report that more than onethird of shark and ray species are now threatened with extinction due to overfishing and habitat loss. The World Wide Fund for Nature’s Living Planet Index has tracked drastic declines in marine vertebrate populations over the past halfcentury, mirroring the losses seen on land. Essentially, the rich tapestry of ocean life, from great whales to minute plankton, is fraying.
This biodiversity free-fall carries profound implications. Healthy oceans are foundational to services humans rely on, fisheries for protein, coral reefs and mangroves for coastal protection and tourism, and myriad marine genetic resources that could hold medical or industrial value. The erosion of biodiversity undermines the ocean’s resilience to other stresses like climate change. Yet there are glimmers of hope, where strong protections exist, species can rebound. Marine protected areas and no-take reserves have been shown to nearly double the abundance of fish within their boundaries over time, spilling over to benefit adjacent fisheries. The challenge is scaling such successes globally before more species pass thresholds of no return.
Global Responses: Treaties, Targets and Initiatives
Facing this litany of oceanic crises, the world’s governments, often prodded by scientists and civil society, have begun to mount a response. The United Nations has played a pivotal role in galvanising international action for the oceans. A key framework is Sustainable Development Goal 14, Life Below Water, part of the U.N.’s 2030 Agenda, which sets out ambitious targets for conserving oceans and ensuring sustainable use of marine resources. These targets range from reducing marine pollution and protecting coastal ecosystems to ending overfishing and protecting at least 10% of marine and coastal areas by 2020. Progress, however, has been mixed at best. By the 2020 deadline, the world fell short of the 10% protection goal as only 8.4% of the ocean is currently within protected areas, and other aims, like restoring fish stocks and eliminating harmful fisheries subsidies, also lagged. One assessment bluntly deemed achievement on key ocean targets “a round and inclusive failure” so far. Part of the problem has been chronic underinvestment, SDG14 has been the least funded of all the global goals, with an estimated $175 billion per year needed but only about $10 billion total invested from 2015–2019. This yawning finance gap has left many well-intentioned plans stranded on paper.
Nevertheless there are some notable strides. Marine protected areas (MPAs) have expanded in recent years, up from just 5% of the ocean a decade ago to over 8% today, including the designation of some of the world’s largest reserves in remote oceanic waters. International pressure to curb overfishing has yielded new tools, in 2022, after two decades of talks, members of the World Trade Organisation concurred to ban certain harmful fishing subsidies that contribute to illegal and unregulated fishing. Combating plastic pollution has likewise shot up the global agenda. The U.N. Environment Assembly passed a landmark resolution to negotiate a legally binding global plastics treaty covering the full life cycle of plastics, from production to disposal. “We’re championing a science-based, legally binding agreement that addresses plastic pollution across its full life cycle,” says Professor Trisia Farrelly, coordinator of a global scientists’ coalition pushing for an ambitious treaty. If successful, it would be the most comprehensive environmental pact since the Paris Agreement on climate.
Yet, perhaps the biggest breakthrough came in 2023, when nations finally agreed on a High Seas Treaty after nearly 20 years of discussions. Formally known as the BBNJ Agreement (Biodiversity Beyond National Jurisdiction), this treaty, adopted at the U.N., fills a major gap in ocean governance. Until now, the two-thirds of the ocean that lie beyond any country’s exclusive economic zone were governed by a patchwork of rules with little coordination. As a result, only about 1% of the high seas was protected , leaving marine life in the open ocean largely at the mercy of exploitation. The new High Seas Treaty creates a framework to establish marine protected areas on the high seas and requires environmental impact assessments for activities in international waters. It also addresses sharing of marine genetic resources and capacity-building for developing states. “The high seas are humanity’s greatest global commons but only about 1% is currently protected,” noted the WWF’s oceans chief in welcoming the treaty . The agreement is indispensable to achieving the recently adopted global target of 30% ocean protection by 2030; a pledge made by countries in the 2022 Global Biodiversity Framework. As of late 2024, over 90 countries have signed the high seas pact and a handful ratified it, inching it toward entry into force. The focus now turns to implementation, turning legal text into actual patrolling of remote waters and enforcement of rules, which will be the true test of the treaty’s efficacy.
Another significant initiative along similar lines is the United Nations Decade of Ocean Science for Sustainable Development (2021–2030). This ten-year effort, led by UNESCO’s Intergovernmental Oceanographic Commission, is rallying researchers and governments to boost marine science, innovation, and knowledge-sharing. The goal is to provide decision-makers with better tools and data to manage ocean resources and protect ecosystems. As we reach the Decade’s midpoint in 2025, the Nice conference will take stock of progress and try to accelerate scientific collaboration. Already, projects under the Ocean Decade are tackling issues from mapping the entire ocean floor (approximately 20% mapped at high resolution) to ameliorating ocean acidification monitoring and early warning systems for ocean hazards. In the long run, such investments in knowledge, coupled with traditional indigenous ocean wisdom, as some experts highlight, could yield dividends in smarter conservation and resource management.
Cooperation, Challenges, and the Road Ahead
As the 2025 U.N. Ocean Conference convenes, it serves as both a sobering report card and a rallying cry for the international community. The conference is expected to produce a high-level political declaration, pointedly titled “Our Ocean, Our Future: United for Urgent Action,” which will stress the need for “significant and accessible” funding for ocean action. Undoubtedly, adequate financing and capacity-building for developing nations will be central to mobilising all actors, governments, businesses, and local communities, in a truly global effort. The Nice conference will also seek to conclude a “Nice Ocean Action Plan,” focusing on finishing pending multilateral processes (plastics treaty), deploying finance for a sustainable blue economy, and strengthening marine science in policymaking. These priorities reflect a recognition that piecemeal steps are not enough; what’s needed is an all-hands approach, from the halls of the U.N. to fishing docks and boardrooms.
The effectiveness of the U.N. and other multilateral institutions in salvaging the oceans will ultimately be judged by outcomes, not promises. On that score, the record is mixed. On one hand, the U.N. has proven indispensable in forging consensus on broad visions and new legal framework, be it the SDGs, the Paris Climate Agreement, or the High Seas Treaty. The very fact that 193 countries could agree to a comprehensive ocean treaty in 2023, at a time of geopolitical frictions, underscores the U.N.’s unique convening power. This success “bucked the trend” of waning international cooperation, analysts noted, demonstrating that collective action is still possible. The U.N. also amplifies the voice of vulnerable states like small island nations, which have been pivotal in pushing ocean issues to the forefront of global climate and biodiversity talks. Their moral authority and firsthand experience of ocean threats have galvanised broader support for ambitious measures such as the 1.5°C climate target and the 30×30 ocean protection goal.
On the other hand, lofty declarations have not yet translated into sufficient on-the-water change. The implementation gap remains a chasm. Despite the fanfare of the first two U.N. Ocean Conferences (2017 and 2022) and thousands of voluntary commitments made by governments and companies, the overall trajectory of ocean health is still downward by many metrics . Overfishing continues in many regions, plastics production is actually increasing, having quadrupled in the last 40 years, and carbon emissions remain on a path that could cook the coral reefs and polar ecosystems that we haven’t yet lost. Part of the challenge is that the U.N. can encourage and coordinate, but it cannot enforce. Compliance with agreements, from illegal fishing crackdowns to emission cuts, depends on national political will and resources. In some cases, global trade and economic pressures still incentivise harmful practices; subsidies that drive overfishing have been estimated at $22 billion a year, and only now are they being curbed. Moreover, geopolitical tensions can spill into environmental arenas, witness how disputes in other domains sometimes stall climate or conservation funding pledges.
To truly turn the tide, experts argue that international cooperation on the ocean must become both more ambitious and more accountable. “We need a transition to a true ‘blue economy’ one where our activities in the ocean enhance nature, not degrade it,” says Prof. Andrew Jeffs of Auckland University, spotlighting ecosystem-based management over shortterm exploitation. That means integrating ocean health into economic decisions, phasing out harmful subsidies, and investing in restoration and sustainable industries from climate-resilient aquaculture to marine renewable energy. It also means better coordination across the myriad institutions that govern the sea, from regional fisheries bodies to the International Maritime Organisation, to ensure efforts aren’t undermining each other. The U.N.’s role here can be to harmonise standards and shine a spotlight on laggards. Transparency in how countries uphold their commitments will be key; some have suggested “oceans COP” meetings akin to climate COPs to annually assess progress on ocean targets.
The final ingredient is encouraging actors beyond national governments. The theme of the 2025 conference explicitly calls for “all actors” to get involved, recognising that NGOs, scientists, indigenous communities, and businesses all have crucial parts to play. In recent years, coalitions of philanthropies and companies have pledged sizeable funds for marine conservation, while indigenous-led protected areas and community fisheries management have gained recognition as effective, equitable solutions. Technology and citizen science are enabling better monitoring, from satellite tracking of fishing fleets to beach cleanup data apps, enhancing public engagement and enforcement. If the story of climate action in the 2010s was one of energising cities, companies, and youth movements to complement international agreements, the story of ocean action in this decade may be similar. The U.N. can champion these inclusive alliances, but it will require sustained pressure from the ground up to hold leaders accountable.
Navigating the Future: Hope on the Horizon?
The challenges engulfing the oceans are undeniably vast, but the momentum for change is building. As delegates assemble in Nice, they carry not just the weight of problems but the buoyancy of recent victories, a new treaty here, a successful local conservation project there, that suggest a more sustainable relationship with the ocean is still within reach. History shows that humanity can come together to solve environmental crises (the recovery of the ozone layer under the Montreal Protocol being a prime example). Impelling international cooperation on the oceans may be even more complex, given the ocean’s status as a global commons and the diffuse nature of the threats. Yet, through the U.N. and other fora, countries have begun to chart a common course.
The 2025 U.N. Ocean Conference will be a litmus test of that collective will. Will nations back their rhetoric of “urgent action” with the financing and enforcement needed? Will emerging powers and industrialised countries alike find common cause in protecting the blue planet, even as they compete in other arenas? The stakes could not be higher. “It is a challenging time for ocean governance… with international cooperation facing challenges,” observes Prof. Jeffs, noting the headwinds of geopolitics, “however, there are reasons for hope”. That hope rests on recent steps like the High Seas Treaty and on a shared understanding that a healthy ocean underpins life on Earth. In Nice, as policymakers debate and activists rally, one message will resound, to save our ocean is to save our collective future. Accelerating action is not a choice but an imperative, and all actors, from heads of state to coastal fishers, have a role to play in steering our world back from the brink and toward a thriving, sustainable ocean.