[willis936]

This is very wrong. Humans produce about 30 TW of heat. The sun imparts 10 trillion times this amount. If we increased our production by 10,000 then we need to put a small umbrella in space to slightly dim the sun the smallest amount to maintain power balance.

[stouset]

Feel free to do the math yourself. You’ll forgive me for trusting in the calculations of UCSD professor of physics Tom Murphy, who’s written about this extensively.

Edit: Also, your numbers are quite simply incorrect. The 70% of sunlight that doesn’t bounce back into space is about 35,000TW, far from the hundreds of trillions of terawatts you claim. At 2.3% energy growth for the next 275 years, we’ll be adding 7,000TW to this number. That is easily enough to noticeably increase Earth’s equilibrium temperature, and far less than this will be necessary to do so given greenhouse gases which reduce our ability to radiate heat into space.

https://dothemath.ucsd.edu/2011/07/galactic-scale-energy/

[willis936]

Sorry the 13 trillion number was from the total power output of the sun (10^26 W).

The Earth receives 340 W / m^2 on average (not accounting for albedo) [1]. The surface area of the Earth is 510 trillion m^2. Humans release 160,000 TWh / year (18.5 TW) [2]. That means the input power from the sun is 9350x what humans release into the atmosphere. If wind and solar play a larger role in the energy mix then the picture looks even better. I can't see how humans could increase power consumption by multiple orders of magnitude without solving so many other (more difficult) problems. Even if we did, playing games with albedo and/or orbital sunshades are on the table with the comparatively meager means we have today. Any future society using that much power surely could address these issues with ease.

Also, expecting constant growth for the next 275 years isn't really a good projection of current trends. We're already seeing negative 2nd derivatives in energy production and population. There is nowhere left to expand in to. The world has become very small very fast.

1. https://earthobservatory.nasa.gov/features/EnergyBalance/pag...

2. https://www.e-education.psu.edu/egee102/node/1925

[stouset]

> If wind and solar play a larger role in the energy mix

The whole point of this debate was that fusion will not unleash a new era of unlimited cheap energy. My argument is that not only will it not, it can not. Will we have more energy available to us than before? Certainly. But all it will do is push us closer to fundamental thermodynamic limits of the Earth's ability to radiate excess heat into space.

Replacing 18.5TW of current power generation with 185TW (10x!) of fusion capacity will already start putting us frighteningly close to those limits. 10x on top of what we have today sounds like a lot, but nearly 90% of the global population today lives in poverty. Bringing them up to a developed-world standard of living will likely eat up well over 100% of that additional budget. Can we augment that with solar? Certainly! But this is hardly "unlimited" energy. A 10-fold increase in energy output will buy us maybe 150 more years of growth.

You may not be happy with it it, but this is the graph of Earth's equilibrium temperature given a consistent 2.3% annual increase in (non-solar) power generation:

https://dothemath.ucsd.edu/wp-content/uploads/2011/07/tmp.pn...

I encourage you to run the numbers yourself. They are correct. And this is treating the Earth as a perfect blackbody which it is not. These numbers are worse when you consider greenhouse gases, even if we manage to somehow go back to pre-industrial levels of carbon in our atmosphere.