None like it hot!

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Mother Superior
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None like it hot!

Postby Mother Superior » Thu Nov 06, 2008 12:19 pm UTC

So, I'm needing some help with this conundrum I've been dreaming up. Basically, if an alien species found a way to block a certain amount of sunlight from reaching Earth, how much would they need to block out in order for the human race to be still able to barely survive, by for example sheltering at the equator?
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nilkemorya
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Re: None like it hot!

Postby nilkemorya » Thu Nov 06, 2008 3:36 pm UTC

Hmmm...tricky. I mean global climatology of that type is really difficult to predict. For example, maybe blocking 10% of the light ends up increasing the total ice covered surface of the world by 5% initially, but this increases the earths albedo which then causes light to reflect further cooling the earth. Also, how long you'd want humanity to be able to survive makes a difference, if it's only for a few thousand years, they could probably block all of it and we'd just have to carry on using available nuclear materials on earths surface to produce enough energy for things like food production and not freezing to death. But yeah, long answer short, I have no idea how you would even go about calculating this...so I'll try anyway!

Assuming we have a highest mean temperature for the year of 308 kelvin, and people need a mean temperature of more than, say, 253 kelvin to survive, and pretending that the climate model is simple...By reducing the incoming sunlight by about 18% you'd decrease temperature by that much.

I hope someone else can do a cooler calculation than that!
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Re: None like it hot!

Postby danpilon54 » Thu Nov 06, 2008 5:05 pm UTC

Well, since the last ice age was only a few degrees colder than the current average temperature, Id say only a small amount. Its really impossible to quantify though. 10% would be quite enough.

Also, its not all about human survival in cold temps. If all our food dies, so do we.
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Re: None like it hot!

Postby Tac-Tics » Thu Nov 06, 2008 7:11 pm UTC

Mother Superior wrote:So, I'm needing some help with this conundrum I've been dreaming up. Basically, if an alien species found a way to block a certain amount of sunlight from reaching Earth, how much would they need to block out in order for the human race to be still able to barely survive, by for example sheltering at the equator?


Given enough preparation time, the human race could probably manage to build artificial shelters to continue surviving the cold even with a significant portion of the sun blocked off.

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Re: None like it hot!

Postby Mother Superior » Thu Nov 06, 2008 7:33 pm UTC

Tac-Tics wrote:
Mother Superior wrote:So, I'm needing some help with this conundrum I've been dreaming up. Basically, if an alien species found a way to block a certain amount of sunlight from reaching Earth, how much would they need to block out in order for the human race to be still able to barely survive, by for example sheltering at the equator?


Given enough preparation time, the human race could probably manage to build artificial shelters to continue surviving the cold even with a significant portion of the sun blocked off.

No preparation time. The sun is blocked off completely without warning. But how d'you envision it'd progress? For example, how long would it take for things to go from "Oh, it's a bit chilly out (Oh, and the sun's disappeared from the sky but never mind that)" To "Oh hey, the Mediterranean just froze solid." (Okay, I don't know if oceans do freeze solid during ice ages, but you get my point).

I am asking this because I've already hollowed out the volcano and I'm getting henchmen from a temp agency, I just need to know which project to go for and the incinerator ray just lacks a certain... oomph.
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Re: None like it hot!

Postby justaman » Thu Nov 06, 2008 7:56 pm UTC

I think it shouldn't be particularly hard to drop the temperature by a significant amount.
Even a relatively small volcanic eruption such as Mt Pinatubo lowered the global temperature by as much as 0.5 degrees C. Larger volcanic eruptions like supervolcanoes are thought the have triggered ice ages, and the eruption of the Deccan Traps is thought to have contributed to the cretaceous-tertiary extinction event. All of these only blocked a small proportion of the global sunlight so I suspect blocking even 50% of the global sunlight for 2-3 years would create significant problems.
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Re: None like it hot!

Postby thoughtfully » Fri Nov 07, 2008 7:43 pm UTC

A sufficiently small (but still self-sustaining) population could probably exist on nuclear and geothermal power. Bring it on! Oh, and we could actually use all those coal reserves without adverse effect. Woot!

Man, it sucks to be the other 5,999,900,000 people, though :(
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Re: None like it hot!

Postby Mother Superior » Sat Nov 08, 2008 8:01 pm UTC

Okay, so let's change the subject slightly here: What would be some of the effects of the Earth's temperature dropping? In the scenario I described above, a giant shield of unknown origin has enclosed the Earth. It is transparent, but only lets a certain amount of sunlight pass through it, to whatever degree was decided upon above (Let's say 15%) which at first only results in, say a rather cold spring and record-colds for the very northern-most countries and eventually will result in a narrow band around the equator being just warm enough for the human race to survive (By which I mean able to grow stuff and have livestock, not living in nuclear-powered bunkers, which is an appealing prospect I grant you [MWUHAHAHAHA!], but not what I'm looking for). What's the middle steps? How would it manifest? Would oceans freeze? Would the weather change considerably? (Other than it being alot colder) Would there be storms? Rain? Snow? Drought? Floods? Tsunamis? Cake?
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Re: None like it hot!

Postby Mother Superior » Sun Nov 09, 2008 6:50 pm UTC

Look guys, when I achieve dominion over the whole world, I promise I'll mention you in my thank you-speech if you help me out. Might even name some continents after ya, how about that? Who wants the keys to a shiny Australia?
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Re: None like it hot!

Postby justaman » Sun Nov 09, 2008 7:56 pm UTC

It would take some time for any really significant effects, there is a lot of inertia in a planetary sized system. I am guessing that the main effects would be a cooling of the surface with progressive increases in ice cover resulting in decreased rainfall (increased snow != rain). Some of the major influence will be on oceanic currents like the Humboldt (already affected by El Nino/La Nina). These currents rely on descending cold water from the Arctic or Antarctic for power and distribute a lot of the nutrients around the major oceans. This will have an obvious effect on air temperatures in the countries which are near the current.

The most likely scenario is that the earth will snowball. How long this will take is anyone's guess.

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Re: None like it hot!

Postby Katrina » Mon Nov 10, 2008 2:33 am UTC

This has already been explored in depth, the term you're looking for is "Nuclear Winter". Take out any holes blown into the ozone layer, remove any secondary / tertiary problems of pollution due to soot and you've your answer.


As an aside, the deep carbon cycle would effected due to ice coverage.

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Re: None like it hot!

Postby Tass » Sun Nov 16, 2008 7:53 am UTC

nilkemorya wrote:Assuming we have a highest mean temperature for the year of 308 kelvin, and people need a mean temperature of more than, say, 253 kelvin to survive, and pretending that the climate model is simple...By reducing the incoming sunlight by about 18% you'd decrease temperature by that much.

I hope someone else can do a cooler calculation than that!


I'll try then. As has been stated many times, the problem is very complicated and depends on currents, atmosphere, albedo and so on. Asuming it could be done this simply there is one big mistake in your calclation, namely that the power iradiated depends on the absolute temperature to the fourth power.

If we still go with a decreese from 308 to 253 thats a 18% decreese in absolute temperatre. 0.824=0.45 so it should take something around a halving of the solar intensity to do that.


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