The Ocean Is the Planet's Climate Engine
Climate is usually told as an atmospheric story. It is mostly an ocean one, and once you see why, the case for connecting finance to ocean health stops looking optional.
Earth is not primarily a land planet in climate terms. The land surface covers less than a third of the globe, while the ocean covers about 71 percent and reaches an average depth of 3.7 kilometers. The atmosphere receives most of the attention in discussions of climate, but its heat capacity is modest beside the volume of water beneath it. Between 1971 and 2018, the ocean absorbed about 91 percent of the excess energy accumulating in the climate system. The atmosphere absorbed about 1 percent.
That difference is enormous. Roughly 396 zettajoules of heat entered the ocean over those decades, enough that a rise of a few degrees in air temperature describes only a small part of what has happened to the planet's energy balance. Most of the added heat went into water, where it slowed the rise in atmospheric temperature while warming the ocean from the surface downward.
Some of that heat remains near the surface and some moves deeper, while currents carry it across ocean basins. It increases evaporation and adds energy to the conditions from which storms develop. Deep water turns over slowly enough that warming there will continue for centuries as heat already absorbed works its way through the ocean. Future emissions still change how much more heat goes in. The IPCC estimates that ocean heat content this century could rise by roughly twice the 1971 to 2018 increase under a low-emissions pathway and by several times that amount under a high-emissions one.
The ocean has also absorbed about 29 percent of human CO2 emissions over the past decade, including roughly 3.4 billion tonnes of carbon in 2024. Some dissolves directly into seawater, where it changes the chemistry and contributes to ocean acidification. Some enters through living organisms. Phytoplankton draw carbon from seawater as they photosynthesize, and when they die a portion sinks into deeper water, where it can remain for centuries.
The capacity of the ocean to keep doing this is changing. Warming and changes in circulation reduced the amount of carbon it absorbed over the past decade by about 7 percent compared with what models estimate rising atmospheric CO2 alone would have produced. The ocean has been taking up both heat and carbon that would otherwise remain in the atmosphere, and in doing so it is changing the physical and chemical conditions that allow it to perform that role.
Currents redistribute heat from the tropics toward the poles and help set conditions far beyond the water itself. The Atlantic Meridional Overturning Circulation carries warm surface water northward and colder deep water southward. Its role in keeping Europe warm has often been overstated, because atmospheric circulation and seasonal heat storage also do considerable work, but it still carries a large amount of heat into the North Atlantic and affects rainfall and storm tracks across the basin. In the Pacific, El Niño and La Niña shift rainfall and temperature patterns over enormous distances. A strong El Niño can bring drought to Australia and southern Africa, flooding to parts of South America, and changes in fisheries along the west coast of North America during the same event.
Most atmospheric water vapour originates as evaporation from the ocean. Tropical cyclones draw energy from warm surface water. Monsoons respond partly to the temperature difference between land and sea. Reservoir levels, crop yields, storm damage and infrastructure design all sit downstream from those processes, even when the ocean itself is hundreds or thousands of kilometers away.
The financial consequences are visible, although ocean conditions do not translate neatly into a line on an income statement. Munich Re estimated global economic losses from natural disasters at USD 320 billion in 2024, with weather events accounting for 93 percent of the total and tropical cyclones alone for USD 135 billion. In 2025, total losses fell to USD 224 billion and tropical cyclone losses to USD 37 billion, helped considerably by the absence of a hurricane landfall on the United States mainland. Ocean heat affects how much energy is available to a storm. The eventual cost depends on where it goes, what it encounters, and how well what has been built there can withstand it.
Consider a lender financing a marine terminal or a wharf-dependent business on the Atlantic coast. Almost everything on the conventional credit side can be modelled closely. Throughput and tariff rates give projected revenue. Operating costs and capital spending give cash flow. Debt service coverage is calculated to two decimal places and tested against a covenant. The security is appraised against comparable sales. A twenty-year amortization is set against the expected life of the asset.
The ocean enters the same file differently. How high the water reaches at that berth during a severe storm depends on surge, waves, local topography and the particular path of the storm. Days of downtime are an estimate. The cost of the next insurance renewal is uncertain, and whether the same coverage will remain available is a decision made by an insurer later. A careful analyst raises each of these questions, but none arrives with the same numerical confidence as revenue, operating cost or debt service. The ocean exposure is more likely to sit in the narrative of the credit write-up while the decision itself rests mainly on the figures.
Hurricane Fiona shows what happens when those exposures become real. The storm made landfall in Nova Scotia on September 24, 2022, and remains the most expensive extreme weather event recorded in Atlantic Canada, with insured damage estimated at more than CAD 800 million. Much of the damage was not insured. The federal government created a CAD 300 million recovery fund, including CAD 100 million for small craft harbours and the recovery of fishing gear lost in the storm.
An economy that operates inside a climate system regulated by the ocean is an economy whose long-term performance depends on ocean health. That dependency is being paid for already, in recovery funds, repair budgets, lost operating days and the terms of the next insurance renewal, often by parties who were not in the room when the original financial decision was made. Blue finance asks whether more of that dependency belongs in the decision at the beginning.
