Ocean Currents and Global Heat
Explain thermohaline circulation (the global conveyor belt) as driven by temperature and salinity differences that cause dense water to sink; describe how the Atlantic Meridional Overturning Circulation (AMOC) transfers heat from the tropics toward Europe; explain that oceans absorb more than 90% of excess heat and ~25% of CO2 from human emissions; explore what would happen to Northern European climates if circulation weakened
What a learner can do afterwards
- Explain that thermohaline circulation is driven by temperature and salinity differences, because cold salty water is denser and sinks
- Describe how the Atlantic Meridional Overturning Circulation carries tropical heat north and contributes to the mild Atlantic air that reaches Northern Europe
- State that the ocean has taken up more than 90% of the excess heat and about a quarter of the carbon dioxide people have added
- Explain how a weaker AMOC can partly offset warming that would otherwise occur in western Europe
1 · Read
You already know ocean currents move heat around the planet. Some of the biggest currents are not pushed by wind alone. Deep in the ocean, heavy water sinking sets a slow loop moving. Scientists call that loop thermohaline circulation and nickname it the ocean conveyor belt. Thermo means heat and haline means salt.
Near the Arctic, seawater gets very cold, and when sea ice forms, it leaves extra salt behind in the water below. That water is now cold and salty, which makes it denser than the water around it, so it sinks straight down. This sinking drives the ocean conveyor belt, drawing warmer surface water north.
The ocean softens what burning fuels does to the planet: it has taken in more than 90% of the extra trapped heat and about 25% of the carbon dioxide people add.
The bars show percents: more than 90% of the extra heat, about 25% of the extra carbon dioxide.
Emma lives in London, UK. Her cousin lives in Winnipeg, Canada, nearly the same distance from the equator. Yet Emma's winters are far milder. Winds blowing off the Atlantic reach London already mild. A system of currents called the Atlantic Meridional Overturning Circulation, or AMOC, helps keep that ocean topped up with tropical heat before the water cools, sinks, and heads back south. Winnipeg sits deep inside a continent, far from that sea air.
A weaker AMOC carries less warm water north. This can partly offset the warming greenhouse gases would otherwise cause in western Europe. Under projected gradual weakening this century, the region is still expected to warm overall.
Cold, salty water sinking drives the conveyor belt, and the heat it carries north is part of why places like the UK have mild winters.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.