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Thread: Cold earth

  1. #1 Cold earth 
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    How long would it take the earth to cool down and what would the eventual temperature be under the following three hypothetical conditions?

    1) The sun's radiation is taken away completely (geothermal action remains).
    2) All geothermal action stops completely (the sun's radiation remains).
    3) Both the sun's radiation and geothermal action stops completely.


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  3. #2 Re: Cold earth 
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    Having us do your homework? :-D

    Quote Originally Posted by Burger
    1) The sun's radiation is taken away completely (geothermal action remains).
    The heat produced by the planet is probably insufficient to keep the surface warm without the Sun. Although its heat is unrelated to the Sun, the core will likely keep going while the surface cools. Depending on how much thermal radiation is retained by the atmosphere, the planet will likely keep warm for a brief while, but afterwards will at the least turn into a frozen ice-world.

    In the study of the Earth, we've found that global blockage of sunlight caused by catastrophic events has triggered global drops in temperature. This seems to occur even though the sun is still heating the upper atmosphere, and the core is still hot. So it's probably safe to assume that at least the surface will become an ice cube.

    Quote Originally Posted by Burger
    2) All geothermal action stops completely (the sun's radiation remains).
    We'd probably experience little if any difference in surface temperature, although volcanic activity would cease, causing global changes in the atmosphere that could actually make things a lot hotter and more hazardous. Volcanoes contribute a lot to our planet's atmosphere.

    Quote Originally Posted by Burger
    3) Both the sun's radiation and geothermal action stops completely.
    Theoretically we could get as cold as possible. Probably several hundred degrees below zero, until every last element capable of freezing and vacuum ablating disappears. We'll be like Mars, only colder than Pluto.


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  4. #3  
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    Thanks for the effort Wolf!

    I'm definitely not having you do my homework though! I'm 34 years old and working in a normal corporate environment where science doesn't feature at all.

    What prompted my question is the fact that I've recently started jogging in the early morning before work and for the first time in a long while really felt how much colder it is at 4 or 5 am than it is in the afternoon. Where I live there is often a 20 Celsius difference between early morning and afternoon temperatures without any major changes in weather. This means that the earth (atmosphere) actually loses it's temperature remarkably quickly in the absense of solar radiation and I was wondering if this drop of 20 Degrees C within half a day would continue at the same rate if the sun stayed away for another 10 or 20 hours or so.

    Would we end up at -40 if the sun didn't shine at all for a whole day?
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  5. #4  
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    A lot of the heat you feel has to do with the ground surface. Deserts are very poor absorbers of heat, so in the day they reflect all the heat from the sun, making things hot, and at night they have retained no heat so the desert gets nearly as cold as it was hot.

    So where you are makes a lot of difference.

    If the Sun didn't shine for a day, you'd probably just experience the same temperatures as night. However as long as there's an atmosphere your area is being effected by thermal changes in other regions of the world.
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  6. #5  
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    Where I live there is often a 20 Celsius difference between early morning and afternoon temperatures without any major changes in weather.
    You are not getting the right impression based on your very local experience. The loss of heat to your immediate surrounding (your city), is not all due to radiation into space. Some of what you feel will be due to convection and diffusion, e.g. heat transported by wind, caused by variations of pressure due to the local changes with day-light. What I mean is, you feel cooler/warmer because a) heat is lost to space, and b) heat is transported to/from your neighbor city. Think of it as an aerial "tide". It's hard to make an estimate of both effects, but if you want to know more about (semi-)global changes I would suggest to look up data on something of larger scale. For example, it would be interesting to see a plot of average temperature of the Pacific ocean vs. time over 24 hours. It might surprise you how much energy is stored in these huge bodies of water.
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