Gulf Stream and Atlantic Overturning

Warm water flows north at the surface, cold water returns south below.

Scientists call this loop the Atlantic Meridional Overturning Circulation, or AMOC. The Gulf Stream is its best-known part, and together they help shape the climate of north-west Europe.

Updated 16 October 2026 · 5 sources

Warm north on top
Cold south below
Measured every hour
Big currents, plain English

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THE SHORT ANSWER

Two streams,
one big loop.

The Gulf Stream is a current; the AMOC is the whole loop.
They are related, but they are not the same thing.

THE LOOP

A conveyor of heat

Copernicus Marine says the AMOC accounts for around 90% of the northward ocean heat transport across the Atlantic, sinking cold and salty in the far north.

See the numbers

MEASURING

Moorings and cables

Since 2004 the RAPID array at 26°N has measured the overturning every hour instead of every five years, using moorings and even old telephone cables.

How it is measured

CLIMATE

Milder winters

Ocean heat stored in summer is released in winter and carried east by westerly winds, giving Europe its characteristically mild winters.

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A coastal garden in winter sunshine with tall cabbage palms and green shrubs beside a low stone wall, the sea beyond — AI-generated image, not a photograph of a real person or place.

HOW SCIENTISTS MEASURE IT

Watching a current
the width of an ocean.

The RAPID project at 26°N, between the Bahamas and Africa, combines three kinds of measurement to estimate the overturning every hour.

Moorings across the Atlantic
Anchored wires with floats carry instruments that record temperature and salinity hourly on the east and west sides of the ocean.
Density into flow
Differences in seawater density between the two sides are turned into north-south flow using a principle called geostrophy.
A voltage in a cable
Salty seawater moving through Earth's magnetic field induces a voltage in submerged telephone cables across the Florida Strait, tracking the current.
Add the wind
Winds push surface water too. This Ekman transport is small on average, 2 to 4 Sv, but causes the largest short-term swings.

TWO NUMBERS WORTH KNOWING

A huge flow
of heat.

One figure for the heat the overturning carries,
one for the size of the Gulf Stream itself.

1.2 PW

Heat carried north by the AMOC

RAPID says the AMOC carries 1.2 petawatts of heat northwards, a quarter of the combined global atmosphere-ocean poleward transport and like the output of 1.2 million power plants.

HEAT · RAPID

≈ 30 billion kg/s

Gulf Stream flow along North America

Copernicus Marine describes the Gulf Stream as the largest current in the North Atlantic, carrying about 30 billion kilograms of water per second, 5 to 15°C warmer than surrounding waters.

WATER · COPERNICUS

RAPID's 2004 to 2024 record revealed a major downturn of the overturning in 2010 to 2011 that marked the start of a sustained decline since then.

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What does the
evidence say?

Pick a common claim about the Gulf Stream or the AMOC. The bar shows how strongly the sources on this page support it.

Based on Copernicus Marine Service and the RAPID project at the National Oceanography Centre, which summarise IPCC assessments.

Claim check

Choose a claimThe AMOC will weaken this centuryThe ocean keeps Europe mildIt will shut down before 2100The Gulf Stream will switch offThe AMOC only changes over centuries

The AMOC will weaken this centuryVery likely

RAPID cites the IPCC: the overturning is very likely to weaken over the 21st century, and climate models consistently project weakening.

The ocean keeps Europe mildPart of the story

Copernicus says the Atlantic acts as a heat reservoir and westerly winds carry that heat east. The AMOC contributes 2 to 3°C to European winter temperatures.

It will shut down before 2100Not expected

There is medium confidence it will not shut down before 2100, though RAPID notes this is physically plausible and the risk rises after 2100 under higher emissions.

The Gulf Stream will switch offUnlikely

Copernicus says an AMOC decline would reduce the Gulf Stream's warm water transport but not shut it down, because much of the flow is driven by wind.

The AMOC only changes over centuriesNot so

Hourly measurements showed it varies on timescales from days to a decade, which surprised scientists who expected decades to centuries.

Sources: Copernicus Marine Service explainer on the AMOC; RAPID 26°N array, National Oceanography Centre (including its summary of the IPCC Special Report on the Ocean and Cryosphere).

Scientists in safety gear seen from behind lowering a tall yellow mooring buoy from the deck of a research ship into a grey ocean — AI-generated image, not a photograph of a real person or place.

WHY IT MATTERS

Salt, ice
and sinking water.

The loop is driven by differences in temperature and salt. In the North Atlantic, warm water cools, becomes denser and sinks, then flows south along the ocean floor. Copernicus Marine says Greenland's melting ice has added around 5,000 km³ of fresh water since 1993, making surface water lighter so it sinks more slowly.

The Royal Meteorological Society notes that about 20,000 years ago, when North Atlantic waters did not sink as deep, the UK climate was colder and more variable. Copernicus says the AMOC has been stable through the last 11,700 years.

In conversation

Questions people ask

Is the Gulf Stream the same as the AMOC?

No. Copernicus Marine says the Gulf Stream forms from the AMOC combined with the wind-driven North Atlantic subtropical gyre, which is two to ten times larger than the AMOC part of the flow.

Why is Porto milder than New York?

They are at about the same latitude, but Copernicus notes New York ranges from about -2.2°C in winter to 29.5°C in summer, Porto from 5°C to 26°C, because winds from the Atlantic warm the air in winter and cool it in summer.

How do scientists measure the AMOC?

Since 2004 the RAPID array at 26°N has used moorings, a cable across the Florida Strait and wind data to estimate the overturning every hour. The moorings are now serviced every 18 months.

Is the AMOC slowing down?

RAPID's record shows a major downturn in 2010 to 2011 and a sustained decline since. Climate models project further weakening over the 21st century.

Would a weaker AMOC cool Britain?

Copernicus says a decline could significantly cool north-western Europe, by 2 to 3°C, despite global warming, and shift rainfall patterns. Changes would still sit alongside greenhouse warming.

Sources

Each figure on this page comes from the sources below.

The ocean's
slow conveyor.