The Unknown Oceans

Earth’s climate has always been in a state of steady, endless imbalance, flux, and readjustment. This is almost entirely due to the constantly flowing, tidal vastness of the oceans.

The world’s five interconnected oceans loom as a source of mystery. While scientists have mapped the surface of Mars and the Moon, 80% of the oceans are unmapped, and are among the greatest unknowns on Earth. A majority of people can only gaze out at the ocean horizons stretching around the globe or walk in the shallows along the coast.

That is all most people ever see or experience.

The ponderous, orderly, ceaseless, and silent underworld movements of deep ocean waters are built upon the planetary memories of a 4.6-billion-year history. Almost nothing in this ocean world changes quickly.

The melting of vast glacial ice caps over the northern landmasses as the planet warmed after 19,000 years ago took the best part of 9,000 years. Oceans rose 120 meters globally, with sea levels climbing at an average rate of approximately 13.3 millimeters—about 1.33 centimeters—each year (or half an inch).

This was the warming phase into today’s 11,700-year-long warm interglacial, the Holocene, merely one cycle in a global glacial reign that has lasted 2.58 million years. Our planet rebalanced itself from icehouse conditions without our permission or help. This planetary-scale de-icing has defined more than 40 similar shifts from an icehouse world to the warm, habitable, and fluctuating environments that characterise much of the Age of Mammals.

The world’s five interconnected oceans are the overwhelming measure of Earth’s capacity to retain heat and offset perpetual ice ages. It’s pure physics. Because water covers nearly three-quarters of the planet (72%), the world is shielded from extreme temperature swings. Land heats and cools rapidly, but the massive, deep mass of the ocean acts as the ultimate planetary buffer zone.

Oceans contain roughly 90% of all the world’s retained heat, while the atmosphere retains less than 1%. Water has an exceptionally high specific heat capacity, meaning it can absorb massive amounts of thermal energy with only a slight increase in temperature.

The movement of tropical warm waters to the Northern Hemisphere is driven by the Atlantic Meridional Overturning Circulation, part of a global ocean conveyor belt circulating on thousand-year cycles. Warm surface waters work their way north, releasing heat into the atmosphere as they reach places like Western Europe.

As a result, the UK and Scandinavia are significantly warmer and more habitable than other areas at the exact same latitude, such as Canada or Siberia—homes to endless tundra, peat bogs, icy, frosted biomes, and ghostly, empty treescapes.

Waters deeper than 200 meters cover 66% to 90% of the total ocean environment, spreading across most of the non-land surface area. The average ocean depth is 2.3 miles, and the deepest point—the Challenger Deep in the Mariana Trench—reaches nearly 11,000 meters, deeper than Mount Everest is tall.

These great ocean waters combine with water vapor, clouds, storms, winds, and solar cycles to ceaselessly redistribute heat. It isn’t just a water blanket—it’s a massive, continuous phase-change engine that moves heat from surface to sky through evaporation, condensation, and cloud cover, reflecting sunlight back into space before it ever hits the deck.

The top three meters of the ocean hold as much heat energy as the entire atmosphere above it. Yet we think we understand the fine machinery of the world’s climate.
The oceans are so vast that their sheer mass prevents the atmosphere from warming at a runaway pace.

The misconception is that thermal transport is primarily atmospheric. If that were true, global air temperatures would be drastically higher than they are today.

Meanwhile, CO₂ makes up roughly four-hundredths of one percent of the atmosphere, playing its vital, priceless role in photosynthesis and the green web of life.

Peter Clack on X