Ocean Currents & Heat Transport: Bergen, Norway sits at 60°N — the sam

Bergen, Norway sits at 60°N — the same latitude as Anchorage, Alaska. In January, Bergen averages around 2°C. Anchorage averages around -10°C. That 12-degree spread is not a quirk of local geography. It is the signature of one of the most powerful heat engines on the planet operating exactly as designed.

The Conveyor That Warms a Continent

The Gulf Stream is the piece most people have heard of — a fast, warm river of water running northeast along the U.S. Eastern Seaboard before crossing toward Europe. But the Gulf Stream is only the surface expression of a much larger system: the Atlantic Meridional Overturning Circulation, or AMOC.

AMOC works on a density gradient. Warm, salty water from the tropics flows north at the surface, releasing heat into the atmosphere as it goes. By the time it reaches the North Atlantic — near Iceland and the Labrador Sea — it has cooled enough to become denser than the surrounding water and sinks, sometimes to depths of 3,000 meters or more. That cold, dense water then flows south along the ocean floor, eventually upwelling in the Southern Ocean and tropics to begin the cycle again. The full circuit takes roughly 1,000 years.

NASA

The volume of water involved is staggering. AMOC moves approximately 20 million cubic meters of water per second at its peak — about 100 times the flow of the Amazon River. The heat it delivers to the North Atlantic basin is estimated at around 1.3 petawatts, or 1.3 quadrillion watts. Northwestern Europe effectively runs on that energy budget. Without it, climate models suggest winter temperatures across the British Isles and Scandinavia could drop by 5 to 10°C within decades of a significant slowdown.

Proxy records from sediment cores and ice cores show that AMOC has collapsed before — most dramatically during the Younger Dryas, roughly 12,900 years ago, when meltwater from retreating glaciers flooded the North Atlantic, disrupting the density gradient and triggering a rapid return to near-glacial conditions across Europe. The transition happened in as little as a decade. Current research, including a widely discussed 2021 paper in Nature Climate Change using statistical fingerprinting methods, suggests AMOC is now at its weakest point in at least 1,000 years, though the precise trajectory remains contested.

NASA / NOAA

The Pacific Side: ENSO's Global Reach

While AMOC shapes baseline climate for the North Atlantic region, the El Niño–Southern Oscillation drives year-to-year variability across a far wider area. ENSO is a coupled ocean-atmosphere system centered in the tropical Pacific, oscillating between warm phases (El Niño), cool phases (La Niña), and neutral conditions on a roughly two-to-seven-year cycle.

During El Niño, a pool of anomalously warm water — sometimes 2 to 4°C above average — spreads across the central and eastern tropical Pacific. That shift reorganizes the atmospheric circulation globally. The jet stream over North America strengthens and shifts south. The southern U.S. gets wetter. The Pacific Northwest and parts of Canada get drier and warmer. Australia, southern Africa, and South Asia often see drought. The 1997–98 El Niño, one of the strongest on record, contributed to an estimated 23,000 deaths and $45 billion in economic losses worldwide.

La Niña reverses the pattern: cooler-than-average sea surface temperatures in the central Pacific, a more active Atlantic hurricane season, and drought conditions across the southern tier of the U.S. The 2020–2022 triple-dip La Niña — three consecutive La Niña winters — was associated with severe drought across the American Southwest and record flooding in eastern Australia.

The mechanism that makes ENSO so consequential is teleconnection: changes in tropical sea surface temperatures alter the position and strength of the jet stream thousands of kilometers away, effectively writing the seasonal weather script for large portions of the globe months in advance. ENSO state is one of the few physical signals that gives seasonal forecasters genuine predictive leverage.

NOAA

Nothing major shifted on either the AMOC or ENSO front this week, but both systems are worth tracking continuously — their states set the table for nearly every significant weather and climate story that follows.

Marine Heatwaves: The Emerging Variable

Sea surface temperature anomalies don't only matter when they organize into ENSO patterns. Marine heatwaves — discrete periods when ocean temperatures exceed the 90th percentile for a given location and time of year for at least five consecutive days — have increased in frequency by roughly 50 percent since 1900 and in duration by about 17 percent. The 2013–2016 Northeast Pacific marine heatwave, nicknamed "the Blob," pushed temperatures 2 to 6°C above normal across a region stretching from Alaska to Baja California, triggering mass die-offs of seabirds, sea lions, and salmon, and contributing to toxic algal blooms along the West Coast.

Marine heatwaves interact with ENSO, AMOC, and baseline warming in ways that are still being characterized. What is clear is that they are no longer rare events — they are a recurring feature of a warmer ocean, and their ecological and atmospheric consequences are measurable.

Field Notes

• ENSO state is updated monthly by NOAA's Climate Prediction Center and is freely accessible — knowing the current phase gives useful context for interpreting any seasonal forecast you encounter.
• AMOC strength cannot yet be measured directly from a single instrument; the RAPID array at 26.5°N in the Atlantic has been continuously monitoring it since 2004 and is the primary observational dataset to follow.
• A marine heatwave in your region's adjacent ocean is worth noting even if it doesn't generate headlines — it can suppress fisheries productivity, fuel coastal fog, and alter storm tracks for months afterward.