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Comment by theandrewbailey | Hacker News Reader

If by 'mass of the earth', you only count the solid parts, yes. But in the astronomical/gravitational sense, it includes the atmosphere. When things are burned, carbon is combined with oxygen to form carbon dioxide. Carbon dioxide is plant food: photosynthesis converts it into sugar, and plants transform that into other forms of solid carbon. Given enough time, it forms wood, oil, coal, etc.[0]

When will it affect gravitational forces? Almost never. Earth's mass is only truly lost when rockets, satellites, and other ejecta leave the gravity well, and the slow stripping away of the atmosphere.[1]

[0] https://en.wikipedia.org/wiki/Carbon_cycle

[1] https://phys.org/news/2016-07-curious-case-earth-leaking-atm...

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> is combined with oxygen to form carbon dioxide

Isn't that some mass will be get converted to energy while burning? So the weight of the resultant CO2 will be less than the fuel burnt.

Yes, due to quantum physics, the end products of comubstion weigh slightly less than the starting products. But this change is so minisqule that you can basically ignore it.

If the energy is used to move something, then by special relativity the object increase the mass [1], and the difference disappears. If the energy is used to heat something, the object increase the mass, and the difference disappears. If the energy is stored elsewhere, also the difference disappears.

The only way to reduce the mass of the Earth (including the atmosphere) is to beam the energy to space, for example using the energy using a giant laser pointed to the sky. A simple solution is to wait until the heat of the atmosphere makes some radiation that escape to space.

Anyway, even if all the energy we produce escapes, it's extremely small, so you can ignore it for all practical purposes.

But it's worse, because the Sun send heat to the Earth. So you have energy going out that decreases the mass of the Earth, and you have energy going in that increases the mass of the Earth. The average temperature of Earth is increasing, so inbound energy/mass is wining.

But it's more complicated because hydrogen and helium in the top of the atmosphere is blow away by solar wind, and solar wind brings some new hydrogen. My guess is that the mass of this exchange is much bigger than the mass of the exchange of energy, but I'm not sure.

[1] Modern books of special relativity don't like to say that the mass increase, because there are some technical problems. If there is no physicist nearby, it's a good approximation.

I finally had some time for hard numbers. (I hope I didn't mess the units.)

From https://en.wikipedia.org/wiki/World_energy_supply_and_consum...

> In 2019 TES was 606 EJ and final consumption was 418 EJ, 69% of TES.

It looks like 75% of it is from fossil fuels. In a power plant that produces electricity, the output is less than a half of the heat produced by the oil/coal/gas. So 606 * .75 * 2 that is like 1000 EJ. In a simplified world, all that energy becomes heat that escape to space after a while.

To get the mass, you must divide it by c^2 https://www.wolframalpha.com/input?i=1000+ExaJoule%2Fc%5E2 and the result is 1200kg (24000 pounds) per year. That's like launching to deep space an elephant per year or a small car per month.

The total mass of the Earth is approximately 6×10^24 kg. So per year we are "launching" 2×10^-21 of the mass of the Earth, that is impossible to notice.

Fake Edit: I just noticed that I forgot to include the heat produced by natural radioactivity that is higher than the energy we use. It's probably also a small number compared to the mass of the Earth, but it's left as an exercise for the reader.

Google says energy of combustion for hard coal is 25 MJ/Kg. E = mc^2 gives 278 picograms of mass lost per kilogram burned in ideal combustion. Consider the amount of earth's mass that is coal and reduce it again by 278e-12 / 1000 to find Earth's mass loss if you did complete combustion of all coal on earth.

Fun napkin math but probably wouldn't make my list of top 10 concerns for humanity.

Ever so slightly, but that mass is regained when the C and O2 separated again.

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