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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 b

by adekok 10y ago

> 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". --- [1] https://en.wikipedia.org/wiki/World_energy_consumption https://en.wikipedia.org/wiki/World_energy_consumption [2] https://en.wikipedia.org/wiki/Solar_energy https://en.wikipedia.org/wiki/Solar_energy

LeifCarrotson 10y ago
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_FINAL.pdf 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.pdf http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-spm..., see page 4
drjesusphd 10y ago
> 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.
- ovi256 10y ago
  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.
AnimalMuppet 10y ago
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...

by adekok 10y ago

LeifCarrotson 10y ago

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_FINAL.pdf 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.pdf http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-spm..., see page 4

drjesusphd 10y ago

> 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.

ovi256 10y ago
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.

AnimalMuppet 10y ago

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...