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Comment by serjester | Hacker News Reader

It takes about 80 watts to heat up a liter of water 1° celsius. Global data centers used about 4.16 x 10^14 watts last year [1]. Let's assume we still have a lot more data centers to build so bump that number up 10,000X. Assuming every watt of energy is actually converted to heat and we moved every data center on earth underwater it'd raise the temperate of the oceans (1.3x 10^21 liters) about 0.01°C.

This is a very rough calculation and there's obviously nuances but the point is oceans are HUGE and water has a high specific heat. It's much easier to indirectly heat them with greenhouses gases.

Edit: I clearly need to brush up on my physics. Regardless the effect is still miniscule.

[1] https://www.forbes.com/sites/forbestechcouncil/2017/12/15/wh...

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This seems to confuse Power with Energy. Watts measure Power, which is a rate of Energy.

The specific heat of water is 4182 Joules/kg and its density is close to 1kg/litre, so 4.128 kJ (Energy) will be required to heat 1 litre of water by 1 degree C.

The temperature rise of the oceans will be complicated to work out. Taking the OPs figures, 4.16x10^14 watts / 1.3x10^21 litres gives 3.2x10^-7 watts per litre of ocean, ie 0.32 microJoules of energy added to the oceans every second. The temperature rise of the oceans will depend on how quickly it can dissipate this heat. What are relevant the heat loss mechanisms? Evaporation just moves the problem to the atmosphere. Conduction just moves it elsewhere on earth. Radiation will shift some of it to space (and some reflected back to the earth), but radiation is a property of the surface of the ocean, not of the bulk.

To clarify: 0.32 microJoules of energy are added to every 1 litre of the ocean every second.

Let's fix the math.

Amount of energy consumed from global data centers: 205 terawatt-hours. [0]

Amount of water in the oceans: 1,386,000,000 (km3)~= 1.386*10^21kg[1]

water has a specific heat capacity of: 4,200 J/kg°C [2]

Energy/HeatCapacity/AmountOfWater = 1.268×10^-7 degrees Celsius

[0]: https://energyinnovation.org/2020/03/17/how-much-energy-do-d... [1]: https://www.usgs.gov/special-topic/water-science-school/scie... [2]: https://www.bbc.co.uk/bitesize/guides/z2gjtv4/revision/5

>It takes about 80 watts to heat up a liter of water 1° celsius

You're confusing power and energy here.

The formula for calculating this is: Q = c_p * d * V * (ΔT). Assuming an isobaric specific heat capacity of 4.18 J/(g K) and a density of 1.00 g/cm^3, heating a liter of water 1.00 K would take 4.18 kJ.

Giving OP's number for the volume of water in the ocean, heating the ocean 0.01 K would be 5.4 * 10^22 J. Assuming 365 days in a year, that's 1.7 * 10^15 W, an order of magnitude less than OPs figure for datacenter power-usage.

> an order of magnitude less than OPs figure for datacenter power-usage

You mean the figure that OP first increased by 4 orders of magnitude, right?

> It takes about 80 watts to heat up a liter of water 1° celsius.

1 calorie is by definition the energy requires to heat 1 gram of water 1°C. In practice 1ml.

So ~1kcal to heat 1 liter of water 1°C

1 kcal is ~1.163 watt-hours.

You are making the assumption that moving data centers underwater would also come along with a 10,000-fold increase in the number of data centers? That seems like an unnecessarily hyperbolic approach.

That would mean going from 8.4 million data centers to 840 billion data centers. I mean, come on...

But hey, let's roll with it. What would be the effect on the environment if we literally had 10,000 times more data centers ABOVE ground, for comparison? After all, you are neglecting to take into account the fact that a HUGE amount of the wattage used by existing data centers has been cooling via HVAC, and by switching to underwater cooling their overall watt usage would theoretically drop a good bit due to the efficiency gains.

I believe the GP's point is that even with a 10,000x increase in data center energy consumption, the effect on ocean temperature is tiny.

Sounds like they're just using pessimistic numbers to make the point. Even if you multiply the existing datacenter footprint by 4 orders of magnitude, it still only results in a 0.01C raise in temperature.

I think you are arguing for the same thing your parent comment is? That comment is trying to show that even in the absolute worst case of no efficiency gains and 10,000x increase in data centers the impact that using the oceans to cool them would have on the ocean is absolutely minuscule.

> Assuming every watt of energy is actually converted to heat and we moved every data center on earth underwater it'd raise the temperate of the oceans (1.3x 10^21 liters) about 0.01°C.

Also assuming we have coated the oceans with a perfect thermal insulator. Otherwise this heat would also radiate away, a small fraction going to the atmosphere and a lot of it back into space.

"It takes about 80 watts" - Watt is a measure of power, you need energy instead (Joules / Watt hours / etc )

> every watt of energy

Watt is a measure of power not energy. Did you mean Watt-hour? The specific heat of water is about 4.2 kJ/kg/K. One joule is one watt for one second, that is 1 J = 1 W.s. So one W for one hour (3600 seconds) is 3.6 kJ and is enough to raise the temperature of a kg of water by about 0.9 K

You need to brush up on dimensional analysis :-)

That assumes heat is distributed instantaneously, which it is not. There will definitely be local affects. The question is if those will harm or collapse native habitats.

There's quite a lot of ocean that doesn't hardly have a "native habitat". Most ocean doesn't look like a coral reef, most ocean looks like water sitting on top of dirt.

Unfortunately, the living parts of oceans are also the parts that tend to be easy to get to, and putting stuff farther away will be more expensive. But careful placement may be able to mitigate that.

It is still ultimately a 3D environment where the vast, vast bulk of the 3D environment is not thriving with heat-sensitive life. Our 2D surface intuition misleads us here. Our mental images of the ocean are of the exceptional locations, not the common ones.

Our 2D intuition leads back on track though, since 2D (or really 1D, or whatever fractal dumention represents thecoastliine) is almost certainly where data centers will get built, not on the middle of the pacific.

3D is relevant to the heat dissipation, and floating submerged data centers doesn't sound so difficult, at least, once you have the idea of a data center not on land. Fortunately, you don't have to go to the middle of the pacific to get away from the living parts of the ocean. You just want to get off the continental shelves, which is easier in some places than others.

Conflating power and energy, and not considering the amount of heat that would be dissipated away, completely destroy any meaning this math would have.

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