The Ocean at Its Limit
Climate, Collapse, and the Future of Life
Most of us don’t give much thought to the ocean, and it’s often overlooked in discussions about climate change and the environment. Yet the ocean plays a vital role in maintaining Earth’s stability and is essential for human survival. It covers 71% of the planet’s surface, holds 97% of all water, and its volume is approximately nine times that of the land above sea level. Despite its scale and importance, the ocean is frequently treated as an afterthought.
The ocean absorbs about 90% of excess heat and 30% of carbon dioxide. It acts as a climate regulator and carbon sink, delaying the worst impacts of planetary overshoot. But its buffering capacity is not limitless, and signs of strain are becoming increasingly clear.
One of the clearest warning signs is rising ocean temperature and declining oxygen levels. Unlike land mammals, most marine species cannot regulate their body temperature, making them vulnerable even to slight changes. Warmer water holds less oxygen. This combination forces many species to migrate poleward—to regions with lower temperatures and higher oxygen levels. Marine ecologist Malin Pinsky explains that what is happening now in the world ocean is the largest known migration of life in Earth’s history (Figure 1).
This is not redistribution of marine life but a cascading collapse. As species flee lower latitudes, the ecosystems they leave behind deteriorate. Northern waters may not offer the enough nutrients and habitats for legacy species and newcomers to survive.
The issue isn’t just moving fish, but static human institutions that have failed to adapt to changing ocean systems. Governance frameworks based on historical fisheries are breaking down. Treaties, fishing rights, and conservation laws are being tested and rendered obsolete as fish stocks cross borders. Conflicts are emerging worldwide. Nations now dispute access to fish that have moved into new territories—examples include North Atlantic mackerel disputes, Pacific tuna conflicts, and Arctic boundary negotiations. Without adaptive international frameworks, these tensions will intensify.
Meanwhile, marine populations are collapsing. According to the World Wildlife Fund, marine populations have declined by 56% since 1970 (Figure 2). This is not species extinction but population loss—more than half of marine life gone in 50 years. If this occurred on land among humans, we would call it a humanitarian catastrophe. Because it’s in the ocean, it goes largely unnoticed.
Industrial fishing has been a major driver of population decline. Large predatory fish like tuna, swordfish, and cod have been decimated by massive industrial fleets. Recent assessments show that a third of the world’s fish stocks are overfished.
Daniel Pauly introduced the concept of the “shifting baseline syndrome,” where each generation forgets the ocean’s former abundance and accepts a diminished state as normal. Pauly’s work shows that peak fish catch likely occurred in the 1990s, with global catches in decline ever since—despite what official reports claim. That should be a red flag for future human food supply because over 3 billion people rely on fish a key source of protein. That’s especially true in places like Southeast Asia, West Africa and the Pacific Islands. He also highlights how tens of billions in subsidies sustain industrial fleets that would otherwise be economically unviable, effectively underwriting ecosystem collapse.
Systems ecologist Corey Bradshaw adds that the ocean has absorbed much of humanity’s planetary overshoot—not just carbon but excess heat. As ecosystems collapse, food webs simplify. With the loss of large predators, jellyfish, algae, and smaller fish dominate. Coral reefs are in widespread decline due to warming, acidification, and direct human impact. While we assume the ocean’s vastness ensures resilience, Bradshaw argues that many ocean systems are near or past tipping points. Biodiversity loss is underreported, particularly in deeper or less studied regions. Public awareness and policy lag far behind scientific understanding.
Pollution adds further stress. Fertilizer runoff creates coastal dead zones, where algae blooms deplete oxygen. Plastic pollution is overwhelming even in remote regions. Ocean acidification, caused by carbon absorption, dissolves the calcium-based structures of plankton and coral, undermining foundational ecosystems.
One of the most critical planetary boundaries under pressure is the Atlantic Meridional Overturning Circulation (AMOC). This global conveyor of ocean currents transports warm surface water poleward and returns cold water at depth (Figure 3). Higher global temperatures have accelerated the melting of Greenland and Antarctic ice, adding fresh water to the North Atlantic. This “freshening” disrupts the sinking of salty, denser water, weakening the AMOC. The result is slower global circulation of heat and carbon, altered rainfall patterns, regional cooling or heating, and rising sea levels. Stratification and deep ocean warming are advancing, as multiple tipping points are now converging.