- Why Scientists Track Atmospheric Carbon With Giant Towers - October 7, 2025
- The Link Between Melting Ice and Rising Sea Levels Explained - October 6, 2025
- How Ocean Currents Help Regulate Global Climate - October 5, 2025
The Ocean’s Incredible Heat Storage System
Picture the ocean as Earth’s giant thermos bottle, capable of storing unimaginable amounts of heat energy. The ocean is the largest solar energy collector on Earth. Not only does water cover more than 70 percent of our planet’s surface, it can also absorb large amounts of heat without a large increase in temperature. This tremendous ability to store and release heat over long periods of time gives the ocean a central role in stabilizing Earth’s climate system. Water has a much higher heat capacity than air, meaning the oceans can absorb larger amounts of heat energy with only a slight increase in temperature.
Between 1971 and 2018, a steady upward trend in ocean heat content accounted for over 90% of Earth’s excess energy from global warming. Think about that for a moment – while we feel the atmosphere warming, the vast majority of that excess heat is actually being absorbed and stored by our oceans. Scientists estimate a 1961–2022 warming trend of 0.43 ± 0.08 W/m², accelerating at about 0.15 ± 0.04 W/m² per decade. The five highest ocean heat observations to a depth of 2000 meters all occurred in the period 2020–2024.
The Global Ocean Conveyor Belt
Density differences in ocean water contribute to a global-scale circulation system, also called the global conveyor belt. The global conveyor belt includes both surface and deep ocean currents that circulate the globe in a 1,000-year cycle. The global conveyor belt’s circulation is the result of two simultaneous processes: warm surface currents carrying less dense water away from the Equator toward the poles, and cold deep ocean currents carrying denser water away from the poles toward the Equator.
This massive circulation system acts like Earth’s climate regulator, constantly mixing and distributing heat around the planet. The whole circuit takes a thousand years. A thousand years, and yet the continual cycling of all that heat and energy affects everything from long-term climate change to daily weather forecasts. Ocean currents act much like a conveyor belt, transporting warm water and precipitation from the equator toward the poles and cold water from the poles back to the tropics. Thus, ocean currents regulate global climate, helping to counteract the uneven distribution of solar radiation reaching Earth’s surface.
How Currents Transport Heat Across the Globe
Warm, fast currents along the western edges of ocean basins move heat from the equator toward the North and South Poles. One such current is the Gulf Stream, which travels along the eastern coast of North America as it carries warm waters from the tropics toward Europe. This warm water, and the heat it releases into the atmosphere, is the primary reason Europe experiences a more temperate climate than the northeastern U.S. and Canada.
For these reasons, the ocean takes a long time to change temperature significantly, whereas land can heat up very quickly (think of the hot sand and cool water at the beach in the summer). Since air travels around, air temperature is also regulated by these principles. Air that is in contact with the ocean will be much cooler from energy transfer between water and air, while air that sits above land will heat up much more quickly. Therefore, coastal climates are much more temperate because a body of water is nearby to regulate the temperature and keep it more constant.
The Ocean as Earth’s Carbon Sink
The ocean generates 50 percent of the oxygen we need, absorbs 30 percent of all carbon dioxide emissions and captures 90 percent of the excess heat generated by these emissions. This makes the ocean not just our planet’s lungs but also its most important carbon storage facility. The ocean acts as a “carbon sink” and absorbs about 31% of the CO2 emissions released into the atmosphere according to a study published by NOAA and international partners in Science.
Though the volume of carbon dioxide going into the ocean is increasing, the percentage of emissions – about 31 percent – absorbed by it has remained relatively stable when compared to the first survey of carbon in the global ocean published in 2004. By absorbing increased carbon dioxide from the atmosphere, the ocean reduces the warming impact of these emissions were they to remain in the atmosphere. Nevertheless the rate in which the ocean absorbs anthropogenic carbon dioxide has approximately tripled from the early 1960s to the late 2010s; a scaling proportional to the increase in atmospheric carbon dioxide.
Temperature Differences Drive Ocean Circulation
Water density is affected by the temperature, salinity (saltiness), and depth of the water. The colder and saltier the ocean water, the denser it is. The greater the density differences between different layers in the water column, the greater the mixing and circulation. It’s like watching a slow-motion lava lamp on a planetary scale – denser, colder water sinks while warmer, lighter water rises and spreads across the surface.
Ocean circulation is controlled by surface winds, by the rotation of the earth and by certain physical properties such as temperature and salinity. Warm water masses carry surface heat accumulated in the tropics towards the poles, thus reducing latitudinal temperature differences. The Gulf Stream, for example, has this role. Currents also move this heat around the world. Increased heat absorption also changes ocean currents because many currents are driven by differences in temperature, which cause differences in density. These currents influence climate patterns and sustain ecosystems that depend on certain temperature ranges.
The Atlantic Meridional Overturning Circulation
Mishonov and coauthors Dan Seidov and James Reagan from NOAA discovered that the the Atlantic Meridional Overturning Circulation (AMOC) current system’s flow remained stable and consistent from 1955 to 1994. However, in the mid-’90s, AMOC strength began to decline and the current began to move slower, which the scientists attribute to the continued warming of the ocean’s surface and the accompanying changes in the salinity of its upper layers. AMOC, which includes the Gulf Stream, carries warm water toward higher latitudes, releasing heat into the atmosphere and bringing cold waters to the tropics. This forms a continuous loop that redistributes heat across the ocean.
According to the latest report from the International Panel on Climate Change (IPCC) – which includes research from hundreds of scientists – the AMOC is “very likely to weaken over the 21st century” due to climate change. Scientists using temperature and sea level records have inferred the AMOC’s strength over the past century, and the evidence suggests that it might have already weakened. If AMOC slows down, the heat exchange will be reduced, which in turn will affect the climate, causing hot areas to get hotter and cold areas to get colder. This could lead to global climate changes, sea level rise, impact on marine ecosystems and other climate feedbacks.
Upper Ocean Currents Are Accelerating
For years, Earth’s ocean has acted as a heat sink for climate change: A large part of the heat generated by human use of fossil fuels is being absorbed by the ocean. And while the deep sea is largely unaffected by this heat absorption, oceanographers have discovered that the upper ocean currents are accelerating. Based on a number of models, scientists predict that in a warming climate, the majority of surface currents across the globe will significantly accelerate. Some of them, like the Atlantic Circumpolar Current around Antarctica, are already shifting.
That acceleration has the potential for huge knock-on effects, including sea level rise, changing fish migration cycles, shifting storm patterns, and more. These changes aren’t just academic curiosities – they’re reshaping weather patterns that millions of people depend on for their livelihoods. And while the deep sea is largely unaffected by this heat absorption, the upper ocean – the ~200 meters closest to the surface – is significantly affected.
Ocean Acidification and Chemical Changes
During this time, the pH of surface ocean waters has fallen by 0.1 pH units. This might not sound like much, but the pH scale is logarithmic, so this change represents approximately a 30 percent increase in acidity. The ocean absorbs about 30% of the carbon dioxide (CO2) that is released in the atmosphere. As levels of atmospheric CO2 increase from human activity such as burning fossil fuels (e.g., car emissions) and changing land use (e.g., deforestation), the amount of carbon dioxide absorbed by the ocean also increases. When CO2 is absorbed by seawater, a series of chemical reactions occur resulting in the increased concentration of hydrogen ions.
The ocean has absorbed enough carbon dioxide to lower its pH by 0.1 units, a 30% increase in acidity. However, carbon dioxide dissolved into the ocean causes seawater to acidify, threatening the ability of shellfish and corals to build their skeletons and affecting the health of other fish and marine species – many that are important to coastal economies and food security. This makes it more difficult for corals, some types of plankton, and other creatures to produce a mineral called calcium carbonate, which is the main ingredient in their hard skeletons or shells. Thus, declining pH can make it more difficult for these animals to thrive.
Global Climate Regulation Without Oceans
Without currents in the ocean, regional temperatures would be more extreme – super hot at the equator and frigid toward the poles – and much less of Earth’s land would be habitable. The global ocean therefore has a role in the regulation and control of the large natural planetary balances. It regulates climate fluctuations. Indeed, the latter would be much more rapid and more powerful if they were only governed by the atmosphere.
This huge mass of water affects the climate by absorbing solar energy and releasing heat. Indeed, the Ocean has a strong heat capacity. It can heat up and cool down very slowly and is capable of storing around a thousand times more heat than that of the atmosphere. The ocean then restores this heat to the atmosphere over periods that can cover several centuries. Altogether these processes enable the ocean to be Earth’s largest thermal reservoir which functions to regulate the planet’s climate; acting as both a sink and a source of energy.
Ocean currents are like Earth’s circulatory system, moving heat from hot tropical regions to cooler polar areas while absorbing the vast majority of excess heat from climate change. Without this natural thermostat, our planet would be a far more extreme and inhospitable place. Did you realize how much our oceans were working behind the scenes to keep our climate stable?
