The Big Picture
Earth's great ocean currents, the El Niño watch area and Greenland's meltwater on one map. Red lines are warm currents near the surface; blue lines are cold, deep currents; the moving dots show which way the water flows. The notes under the map change each day with the latest reports. Click or tap the map to see it full screen.
The Atlantic Meridional Overturning Circulation (AMOC)
A giant loop of ocean currents in the Atlantic. Warm, salty water flows north near the surface (the Gulf Stream is part of it) and gives off heat that keeps northwest Europe mild. Near Greenland and Norway the water cools, grows heavy, sinks, and flows back south along the bottom. Melting ice and heavier rain add fresh water that makes the sinking harder, so scientists watch closely for signs that the loop is slowing.
The North Atlantic Cold Blob
A patch of ocean south of Greenland and Iceland that has cooled over the past century while nearly every other ocean on Earth warmed. Scientists also call it the North Atlantic "warming hole." Many see it as a fingerprint of a weakening AMOC, because less warm water is reaching the area, and some think it is already shaping Europe's weather.
Kelvin Waves
Very long, slow waves that travel inside the ocean rather than on top of it. Along the equator they move from west to east, carrying warm water toward South America, and they help build El Niño. When they reach the coast they turn north and south and can raise sea levels for weeks. At the surface they are only inches high, but hundreds of miles long.
The Southern Meridional Overturning Circulation (SMOC)
The Southern Hemisphere's overturning circulation. Around Antarctica, freezing sea ice leaves its salt behind, making very cold, heavy water that sinks to the seafloor (Antarctic Bottom Water) and spreads north through all the oceans, while deep water rises back to the surface around the continent. This sinking carries oxygen, heat and carbon into the deep ocean. Meltwater from Antarctica makes the surface fresher and lighter, which can slow it down.
El Niño & La Niña
Every few years the tropical Pacific swings between warm and cool phases. In El Niño, the trade winds weaken and warm water spreads east toward South America (Kelvin waves carry much of it), heating the planet and shifting rain, drought and hurricanes around the world. La Niña is the cool opposite. Scientists watch a stretch of ocean along the equator called Niño 3.4: half a degree Celsius (about 1°F) above normal there is the threshold for El Niño; half a degree below is the threshold for La Niña.
Ocean Heat & Marine Heatwaves
The oceans soak up most of the extra heat trapped on Earth. Since 2023, sea surface temperatures around the world have broken record after record, and long spells of unusually hot water, called marine heatwaves, have bleached coral reefs, killed fish and fed stronger storms. Warmer water also expands and raises sea levels, and a warmer, lighter surface layer makes it harder for the ocean's overturning currents to sink.
Polar Ice
The sea ice floating on the Arctic Ocean and around Antarctica, and the great ice sheets of Greenland and Antarctica. Sea ice reflects sunlight and keeps the poles cold. When the ice sheets melt, they pour fresh water into the ocean; fresh water is light and does not sink, which is why it can slow both the AMOC and the SMOC. Arctic sea ice has shrunk sharply since satellites began watching in 1978, and Antarctic sea ice has hit record lows since 2016.