A disclaimer

I am not a climate scientist and may be making mistakes in this article. I'm writing it (with AI aid of course) because there seems to be a lot of weird debate about human heating going on, as if it were bad for the climate. It is bad for the climate, but absolutely negligible compared to the biggest source of heating by far, which is the heating caused by the super well understood greenhouse effect due to human emissions of greenhouse gases.

For example, if your local data centre is running hot, it may be increasing electricity prices in your area, making a lot of noise and taking up space, but the heat from this data centre would not be the main problem; the additional emission of greenhouse gases in generating the electricity is the problem.

I wanted to discuss this in light of the absolutely shocking recent results on ocean warming. The ocean is getting cooked.

The ocean is getting cooked

Every year a team led by the Chinese Academy of Sciences totals up how much heat the ocean has gained. In 2025 the top 2,000 metres of ocean gained about 23 zettajoules more than in 2024, another record (Cheng et al., 2026). A zettajoule is a billion trillion joules, which doesn't help much, so here's another way to put it. Spread over the year, 23 zettajoules is about 730 terawatts of non-stop heating. The whole of humanity - every car, power station, steel mill, data centre and kettle - used about 592 exajoules of energy in 2024 (Energy Institute, 2025), which is about 19 terawatts. So the ocean gained heat at roughly 39 times the rate at which we use energy.

And the ocean takes nearly all of it. Of all the extra heat the Earth has trapped since 1971, about 89% went into the ocean, 6% into the land, 4% into melting ice and only 1% into the air (von Schuckmann et al., 2023). The air is where we feel warming, but the air is a rounding error in the heat budget.

It's also speeding up. The rate at which the Earth gains heat is called the Earth energy imbalance: sunlight coming in, minus what's reflected and radiated back out to space. Averaged over 1976–1995 it was 0.40 watts per square metre of Earth's surface. Over 2006–2025 it was 1.04 (Forster et al., 2026). By 2023 the satellites showed it at about twice the IPCC's best estimate (Mauritsen et al., 2025).

That's the part I find shocking. Not just that it's warming, but that it's warming faster.

So where does the heat come from?

The obvious suspect, if you watch the arguments online, is us, directly. We burn a lot of stuff. Every joule of energy we use ends up as heat in the end, including the electricity running your laptop. So is the ocean heating up because of the heat from our engines, power stations and data centres?

No. Not even close.

Mark Flanner at the US National Center for Atmospheric Research worked this out in 2009. Averaged over the globe, heat from our energy use adds only about 0.028 watts per square metre (Flanner, 2009). Energy use has grown since, so I redid the sum with 2024 figures: 19 terawatts spread over the Earth's surface comes to about 0.037 watts per square metre. Compare that with the 1.04 watts per square metre the planet is actually gaining: our direct heat is about 3.5% of it, and that's generous. The energy from wind, hydro and solar was already part of the flow of sunlight, so it isn't really extra.

The greenhouse effect, on the other hand, is enormous. Since 1750, the greenhouse gases we have added hold in an extra 3.58 watts per square metre (Forster et al., 2026). Carbon dioxide does two-thirds of that. Methane, nitrous oxide and industrial gases do the rest. Direct heat from our energy use is about 1% of it.

The comparison I like best comes from a 2015 paper that asked exactly my question (Zhang & Caldeira, 2015). Burn some fossil fuel and you get two kinds of heating: the heat from the flame, and the heat the resulting CO₂ traps. Within two months the CO₂ has trapped more heat than the flame ever released. Over its lifetime in the atmosphere, the CO₂ traps more than 100,000 times as much. The flame is over in a moment. The gas keeps trapping heat for centuries.

Which brings me back to the data centre. The heat coming off it is real, and it can matter locally: averaged over the continental US our direct heat adds 0.39 watts per square metre, and over Western Europe 0.68 (Flanner, 2009). Locally, that's no longer tiny. But for the planet, and the ocean, what matters is what came out of the chimney of the power station that fed it.

Could it all be natural, the odd El Niño shuffling heat around? Researchers tested that as well. The odds that natural variability explains the rising imbalance are below 1%. The trend only appears once human forcing is included (Raghuraman et al., 2021).

One more heat source, for completeness: the Earth's interior leaks about 47 terawatts (Davies & Davies, 2010). That's more than twice humanity's entire energy use, and it still doesn't matter here. It has been flowing steadily for millions of years, so it isn't what's changing.

Complications

This is where it gets more interesting, and where I have to be careful.

You might expect greenhouse gases to warm the planet by blocking outgoing heat, the infrared that the Earth radiates to space. They do. But a warmer planet also radiates more, and those two effects nearly cancel out. When scientists broke down the satellite data, most of the recent rise in the imbalance showed up on the sunlight side: the Earth is reflecting less sunlight back into space (Loeb et al., 2021; Raghuraman et al., 2021).

Why is it reflecting less? Partly because there's less sea ice, and dark ocean absorbs more sunlight than white ice. Partly because clouds, especially low ones, have thinned. In 2023 the Earth was the least reflective on record, mostly because of fewer low clouds (Goessling et al., 2024). Whether those clouds are thinning because of natural variability, because of warming itself, or because of cleaner air, nobody yet knows. The authors say so plainly.

And the cleaner air is the ironic part. For decades, sulphur from coal plants and ship fuel has made a haze that reflects sunlight and brightens clouds. It's horrible for lungs, and it has quietly cooled the planet. Air pollution cancels about a quarter of the greenhouse warming today (Forster et al., 2026). As we clean it up - rightly, because it kills people - that shield is removed. Cutting aerosols has boosted the heating trend by about 0.2 watts per square metre per decade (Hodnebrog et al., 2024). Sulphur cuts since 2019 alone have added about 0.1 watts per square metre (Forster et al., 2026).

So the story isn't quite "greenhouse gases and nothing else". The gases are the root cause and the biggest term by far. But cleaner air is removing a mask that was hiding part of their effect, and the planet's own responses - less ice, thinner clouds - add to it.

None of these complications bring us back to heat from our engines, though. Every one of them is about sunlight and gases, not flames.

Fight the right battles

If we're going to fight climate change, we need to fight the right battles. Worrying about the heat from a data centre or a car engine is worrying about 1% of the problem. Worrying about the gas coming out of the chimney is worrying about the other 99%.

That's not a reason to love every data centre. There are plenty of good local arguments about power, water, noise and land. But when the question is the climate, the question is the electricity: how much, and how it was made.

The heat stops the moment the flame goes out. The emissions keep trapping heat for centuries.

I said at the start that I'm not a climate scientist, and I may well have got some details wrong. But the headline doesn't depend on details. Every source I found - satellite records, ocean measurements, energy budgets - points the same way, and by a margin of about a hundred to one. The ocean is soaking up heat because of the gases we've put in the air, not because of the heat from our machines.

So when the next argument starts about something running hot, I'll ask a different question: what did it emit to get that hot? Concentrate on emissions, not heat.

Sources

• Cheng, L. et al. (2026). Ocean Heat Content Sets Another Record in 2025. Advances in Atmospheric Sciences. doi:10.1007/s00376-026-5876-0
• von Schuckmann, K. et al. (2023). Heat stored in the Earth system 1960–2020: where does the energy go? Earth System Science Data 15, 1675–1709. doi:10.5194/essd-15-1675-2023
• Forster, P. M. et al. (2026). Indicators of Global Climate Change 2025. Earth System Science Data 18, 3889. essd.copernicus.org/articles/18/3889/2026
• Mauritsen, T. et al. (2025). Earth's Energy Imbalance More Than Doubled in Recent Decades. AGU Advances. doi:10.1029/2024AV001636
• Flanner, M. G. (2009). Integrating anthropogenic heat flux with global climate models. Geophysical Research Letters 36. doi:10.1029/2008GL036465
• Zhang, X. & Caldeira, K. (2015). Time scales and ratios of climate forcing due to thermal versus carbon dioxide emissions from fossil fuels. Geophysical Research Letters 42. doi:10.1002/2015GL063514
• Raghuraman, S. P. et al. (2021). Anthropogenic forcing and response yield observed positive trend in Earth's energy imbalance. Nature Communications 12, 4577. doi:10.1038/s41467-021-24544-4
• Loeb, N. G. et al. (2021). Satellite and Ocean Data Reveal Marked Increase in Earth's Heating Rate. Geophysical Research Letters 48. doi:10.1029/2021GL093047
• Hodnebrog, Ø. et al. (2024). Recent reductions in aerosol emissions have increased Earth's energy imbalance. Communications Earth & Environment 5. doi:10.1038/s43247-024-01324-8
• Goessling, H., Rackow, T. & Jung, T. (2024). Recent global temperature surge intensified by record-low planetary albedo. Science. doi:10.1126/science.adq7280
• Davies, J. H. & Davies, D. R. (2010). Earth's surface heat flux. Solid Earth 1, 5–24. doi:10.5194/se-1-5-2010
• Energy Institute (2025). Statistical Review of World Energy 2025 (energy data, not peer-reviewed). energyinst.org/statistical-review