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Comment by ovi256 | Hacker News Reader

>No more global warming.

Au contraire, my friend.

Unlimited cheap energy would bring on, in time, the next type of anthropogenic warming: the temperature of the planet being raised, not by a greenhouse effect, but by the raw power output of all those fusion reactors. Even if a good fraction of their thermal output is transformed into electricity, the electricity always finishes as decay heat, with very few exceptions.

The solution for that is to move the Earth farther away from the sun, which reduces solar input. Or injection of coolants such as sulphates in the atmosphere. Even with zero solar input, there's still an upper limit on how much decay heat we can release in the atmosphere without boiling ourselves.

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> the temperature of the planet being raised, not by a greenhouse effect, but by the raw power output of all those fusion reactors.

Not that Wikipedia is the best source, but...

World energy consumption is about 12 terawatts [1], whereas the Earth receives 172,000 terawatts in the upper atmosphere. [2]

The difference is 4 orders of magnitude. i.e. The Earth receives in one day the same power as produced by humans in 10-15 years.

I think we're safe.

> The solution for that is to move the Earth farther away from the sun

That's firmly in the realm of science fiction. The power required to move the earth would be so enormous that it could power human technology for billions of years.

i.e. it would be energetically more efficient to use that power to fix the current problem, instead of doing something ridiculous like "move the Earth".

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[1] https://en.wikipedia.org/wiki/World_energy_consumption

[2] https://en.wikipedia.org/wiki/Solar_energy

To complete your rebuttal to the statement "not by a greenhouse effect, but by the raw power output", it's important to compare the magnitude of the greenhouse effect. It would be easy to draw the wrong conclusion, and think that mankind cannot impact the temperature of the planet because it already gets so much energy from the sun that our actions don't matter. This is incorrect.

As you say, the sun provides approximately 172,000 terawatts to the Earth, due to a solar irradiance of 1360 W/m^2 over the planet's cross sectional area of 1.27x10^11 m^2. While this is the correct value for the amount of energy received at the upper atmosphere, only some of it is actually absorbed by the Earth. Currently, approximately 30% of this energy is reflected back to space.

Anthropogenic radiative forcing was estimated by the IPCC in 2011 [1] to contribute approximately 2.29 W/m^2. This is the difference in solar energy absorption caused by human activities (such as releasing CO2). Multiplied by the area of the Earth, this is 290 terawatts of energy, which is many times greater than world energy consumption.

Also note that this figure is rapidly increasing - compare to 1.25 in 1980 and 0.57 in 1950 in that report, or 1.6 in the 2007 report [2].

[1]: http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_SPM_..., see page 12 [2]: http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-spm..., see page 4

> I think we're safe.

Well, it doesn't need to equal the irradiance of the sun to be a big effect. 1% of the sun is still a hell of a lot of extra warming.

At an annual growth rate of 2%, that 12 TW becomes 1% of the sun in 250 years. Not all that long when solutions are 50+ years out. If you're a fan of keeping capitalism going, we're going to need faster growth than that.

Of course this type of warming is not dangerous on a human lifetime timescale. It would also require us to become a level I Kardashev Scale civilization (harnessing all the energy reaching our planet from our star, or the equivalent). But it does set an upper limit on how much can be done on a planet.

Note that "move the earth" would also require insane amounts of energy, which we'd have to generate somehow, and which would generate large amounts of heat...

Source? Compare to how much heat we receive from the sun I doubt our activity adds much heat.

At the moment not really, yes. But he was speaking of the possible scenario with unlimited avaiable energy and therefore much more energy spending ... but I also don't see this as a real concern. Global Human energy output would have to increase by many numbers to make a significant impact.

Someone up thread posted the figures, human energy is 12 terawatts, the earth receives 172,000 terawatts a day, replacing all of energy usage with fusion and then doubling it to 24 terawatts would likely result in a cooler planet (since we'd be producing far less carbon dioxide).

I imagine unlimited cheap energy would help facilitate moving us off this floating rock we call earth.

Unlimited cheap energy on any plant would enable us to implement environmental controls, using that energy, so we could build habitats in hostile atmospheres.

> I imagine unlimited cheap energy would help facilitate moving us off this floating rock we call earth.

With a working small scale fusion reactor we could colonise the entire solar system, the raw materials are all out there but energy is always one of the main issues.

I remember reading back in the 80's a plan for extracting metals, creating metal foam that would float and then dropping them into the ocean (some would be lost to rentry heat but it was a tiny percentage) where a drone ship would sail out and tow them in.

I would love to see something like that in my lifetime.

When energy isn't a concern, what stops you from moving the manufacturing into space?

Cost...

Cost is mostly convertible to energy. (And space I guess, for things like real estate)

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