I’ve finally finished my ocean heat investigation! :)
This whole investigation starts with a 2026 paper by Gregory Johnson [1] (University of Washington and NOAA) in Geophysical Research Letters. Earlier work showed the deep ocean is warming. Johnson asked if the warming is speeding up.
To find out, he combined ship based temperature measurements going back to about 1970 with data from Deep Argo floats, robotic floats that started measuring the deep ocean in regional arrays around 2016. He split the ocean into boxes about 167 km on a side. In every box with enough data, he fit a curve that lets the warming rate change over time.
What he found:
The abyssal ocean (4 to 6 km deep) took up about 5.4 terawatts of heat in 1988 and about 20.2 terawatts in 2018. That’s roughly four times as much.
The deeper ocean above it (2 to 4 km) showed no statistically significant change: about 29 TW in 1988 and 25 TW in 2018.
That 20.2 TW is the number I’ve been comparing every heat source against.
There are very important considerations: the data are sparse, and only about 18% of the ocean’s volume had enough measurements to estimate the acceleration. The 1988 value (5.4 ± 4.9 TW) is itself uncertain, and the 2018 value is 20.2 ± 3.9 TW. So the result is a real signal, but with real error bars. It also shows that the abyss is heating faster, not why it’s heating faster, and that’s the question I’ve been trying to answer.
Over several months I studied ocean temperature records, ran circulation models, tested heat coming up from the seafloor, and built an electromagnetic solver. I wanted to know why the deepest ocean (4 to 6 km down) seems to be warming faster than it used to. Here’s where we ended up.
1. Pressure heating: ruled out
Squeezing water under pressure warms it a little. But the temperature measure scientists use already removes that effect, so it can’t explain the extra warming. This one was easy to close.
2. Water layers moving up and down: possible, but I can’t prove it
When layers of water of the same density shift up or down, the temperature at a fixed depth changes. My calculations matched the overall pattern fairly well (correlation 0.69, with the right direction of change in about 75% of places with data). But the data aren’t good enough to say how much this adds up to worldwide. It could still be part of the story.
3. Changes in deep ocean circulation: not the main cause
I tested whether a slowdown in the deep currents that carry cold Antarctic water north could explain the faster warming. The change went in the right direction but explained only about 2% of it.
4. Heat from the seafloor: still possible, but unproven
I tested three different maps of heat rising from the seafloor and followed that heat through 20 years of changing currents. All three pointed the wrong way to explain the extra warming.
But there’s one thing I haven’t ruled out. What if heat from the seafloor had been building up in the deep ocean long before my simulations started? Changing currents could then move that old heat around without any increase in seafloor heating. As Roger pointed out, we don’t have enough deep ocean measurements to settle this. So I’m leaving it open.
5. Electric currents from changing magnetic fields: ruled out as a main heat source
This was my last idea and the hardest to compute. I built a 3D model of how changing magnetic fields drive electric currents through the ocean, and how much those currents heat the water.
For a strong magnetic disturbance (1,000 nT), the model gave about 25 kilowatts of heating in the deep ocean. That’s roughly a few home space heaters.
The deep ocean’s warming needs about 20 terawatts. That makes the electric current idea hundreds of millions of times too weak, about 813,000,000 times. I also tested the slow weakening of Earth’s own magnetic field. That gave only about 25 watts, roughly a night light. So electromagnetic heating is out as a main heat source, at least for the conditions I tested.
So what do I think is happening?
I think it’s a mix of:
changing deep ocean currents,
heat moving between different layers of water, and
heat coming up through the seafloor.
The ocean gets heat from above and from below, and we know currents can move it around. What I can’t yet say is how much of the faster warming comes from moving water, changing water properties, or heat already stored.
Deep Argo floats are fairly new, older records are very sparse, and huge parts of the deep ocean have almost no measurements. That makes it challenging to pin down a heat source.
Where I’m leaving it
I tested five ideas, and some are ruled out, some are too weak, and some are limited by missing data. I haven’t found a new main heat source, and I don’t think the data support claiming one. My working idea is that ocean circulation and the movement of heat that’s already are key, with seafloor heat still a possible contributor.
It was months of modeling, lots of surprises, and some of my favorite research so far. I’m glad I followed it all the way. :)
References
[1] Johnson, G. C. (2026). Observed multi-decadal acceleration of globally averaged abyssal ocean warming. Geophysical Research Letters, 53, e2026GL124104. https://doi.org/10.1029/2026GL124104
