Active Users:314 Time:15/05/2024 01:44:23 AM
Re: Not THAT ludicrous, just more extreme. (edit) Isaac Send a noteboard - 19/11/2010 07:25:21 PM
So it's daytime is shorter; does that mean the seas of lead freeze on the night side?


No, it's day times are longer by about a hundredfold, and its temp is pretty much the same on both sides, heat transfer through convection happens really quick at those levels of pressure and heat. Venus's atmsosphere is around 100 atm IIRC

I'm only a layman, but it seems like the amount of heat retained and reflected should be about the same whether the half of the surface getting sunlight is the same or varies.


Reflected, pretty much, radiated? Not even vaguely. The effect isn't linear. Stefan-Boltzmann Law requires an object to radiate energy at a rate of the fourth power to temperature. So like, double an objects tmep and it radiates 2^4 or 16 times as much, triple and 3^4, or 81 times as much. This is in Kelvin, so a 20 degree Fahrenheit difference between day and night isn't as much as it sounds like. Take the radiation between the Earth and sun... Divide the sun's surface temp by the Earth's (in kelvin) and raise that to the fourth power. Multiply that by the ratio of the sun's surface area to the Earth, you will see you have the same number as the ratio of the earth's radiation and the sun's (or close to it )

A planet that radiates half the time at a higher temp and half at a lower will radiate away more heat then one which keeps to the same average temp the whole time.

Naturally differences between various places on the planet should vary a lot more, but if there's a big difference between the total heat retained by a spinning versus motionless planet I'm curious to know why.


It reflects a lot of radiation away. Inb thermodynamics radiation, be it normal light like we see or gamma rays or the kinetic energy of a non-light particle acts in 3 ways. Reflect, Absorb, Transmit. Except for neutrinos, anything that hits the earthi is pretty much absurbed or reflected, anything not reflected is absorbed and becomes heat. Try whacking a pile of clay with a hammer a bunch of times and watch it temperature rise, or bending a close hanger back and forth and watch the bent part get nice and hot. All energy which doesn't exit in some other form is heat. All those cosmic rays and particles we talk about our magnetosphere protecting us from, all of those if not reflected or curved away would become heat.

That doesn't even include the effect rotation and an EM field has on weather, which is primarily convective, but heat transfer is a big factor there and convection goes faster when you stir stuff up, try taking two identical hot coffee cups, stir one constantly and let the other sit... which cools faster? This won't change the rate at which the planet radiates heat directly, we don't convect with the vacuum above, but it spreads temp faster, and as mentioned, average temperature does not dictate rate of radiation If I take four steel globes, two at 60 degrees, one at 80, and 1 at 40, those two identical ones will emit less heat via radiation then the the two at 80 and 40, because the one at 80 will emit significantly more heat, as the effect goes with the fourth power - again, in absolute temp. Run this for yourself, 40 f is 277 K, 60 f is 288, and 80 f is 300 K

Treat 277 as radiating 1 unit of heat

the 288 case will emit (288/277)^4 = 1.17 units of heat

the 300 k case will emit (300/277)^4 = 1.38

1+1.38 = 2.38

2x1.17 = 2.34

So 2% more heat radiated for the same average temp, and that's a fairly minimal fluctuation in temperature, only about 4% either way. Using those two examples, let's say the avg temp of a planet went from 40 f to 60 f, it now radiates 17% more energy, yet when this is from a greenhouse effect the same amount of light is hitting it, actually less as more clouds from more water vapor cause more reflection, another of those negative feedbacks, water clouds are a greenhouse gas, but they are also white, so they reflect a lot of light too, Venus, as you may note, isn't white, different albedo than ours.

Edit, hit submit instead of preview and was wondering off on a albedo sidetrack.

Additional questions:

Is a magnetic field thought to play a role in the greenhouse effect, or did you just mention it to give an example of a difference between Earth and her sister planet?


Covered this above, sorry

Twice as much light, really? I didn't think they were THAT much closer to the sun.


Inverse square law, half again the distance means about 1/2 the light

I'm not saying we're identical though, just that Venus provides us an excellent example of how a runaway greenhouse effect really can have dire consequences, despite the claims of those who insist it doesn't matter even if it IS happening here. Too much of that, hell, too much of US policy in general these days, strike me as a rationalized excuse to do nothing, with the incidental effect that those who materially benefit from doing nothing continue doing so. And accuse reputable scientists of bias and greed.


I am one of those people who claims it probably doesn't matter much even if its happening here, or rather, I feel we're probably have a significant effect but its not a sure thing, and the extent is definitely unclear, and I can't think of a lot of downsides to any of the saner temp increase estimates. Personally I wouldn't be surprised if we stopped using fossil fuels in favor of something better if we ended up digging them up and burning them just to add more CO2 on purpose. More rain, warmer temps, and more CO2 are generally beneficial to plant growth, and we have way more tundra to reclaim then shoreline to lose. But I'm utterly open to the science in any direction it goes, I just don't trust what we have as so ironclad right now. Skeptic in my book is usually a good thing.
The intuitive mind is a sacred gift and the rational mind is a faithful servant. We have created a society that honors the servant and has forgotten the gift.
- Albert Einstein

King of Cairhien 20-7-2
Chancellor of the Landsraad, Archduke of Is'Mod
This message last edited by Isaac on 19/11/2010 at 07:33:19 PM
Reply to message
So, I think I found a way to actually prove if Global Warming is happening. - 19/11/2010 01:22:49 AM 603 Views
The idea that CO2 in the atmosphere holds in heat is not in dispute - 19/11/2010 02:13:02 AM 466 Views
One need look no further than Venus. - 19/11/2010 03:22:50 PM 421 Views
To find a ludicrous parallel? - 19/11/2010 04:38:12 PM 368 Views
Not THAT ludicrous, just more extreme. - 19/11/2010 05:29:23 PM 402 Views
Re: Not THAT ludicrous, just more extreme. (edit) - 19/11/2010 07:25:21 PM 353 Views
Re: Not THAT ludicrous, just more extreme. (edit) - 22/11/2010 01:47:15 AM 1021 Views
There are limits as to how much some of this stuff can be simplified - 22/11/2010 04:27:10 AM 559 Views
With apologies for the delay. - 03/12/2010 03:54:26 AM 531 Views
I hate computers sometimes - 03/12/2010 05:10:36 PM 457 Views
Re: - 19/11/2010 02:41:29 AM 454 Views
Entirely agree - 19/11/2010 08:42:51 AM 344 Views
Wouldn't prove anything - and your experiment is very flawed - 19/11/2010 10:57:41 AM 367 Views

Reply to Message