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Re: Not THAT ludicrous, just more extreme. (edit) Joel Send a noteboard - 22/11/2010 01:47:15 AM
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

In that case the issue of a given side being exposed to the sun for a given time far longer than the other seems no issue at all: Temps are the same on both sides, so whether a planet with a very hot/cold side retains more heat than one where the two frequently switch orientations is moot.
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 :P )

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.

But since Venus evidently does the latter, and to an even greater degree than Earth, that's irrelevant here. Albedo seems more important.
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.

A LOT of this seems irrelevant if there's no significant difference between the un/lit sides of Venus; I'm beginning to wonder why you even mentioned the longer days if the greater pressure means they have even less effect on temperature variations than our own 24 hour days. I've bent a few pieces of wire in my day, and I know what happens; I can't recall ever spinning in circles while doing so, so I can't be sure that wouldn't make a difference, but if there is one that analogy fails to demonstrate it. Likewise, convections effects on heat transfer within the planet are irrelevant if pressure is already maintaining an essentially constant temperature across the globe. Regarding the example, is it really accurate to treat the cold and hot sides of a globe as if they were two separate bodies? I'm not convinced albedo is a sidetrack at all, but since heat radiated from planets is almost entirely heat they first absorbed (minus things like the heat of gravity compressing its mass) I was thinking a lot about it and reflected heat from the start.

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

Maybe it's just because I'm the Tangent King, but saying your analysis "doesn't even include the effect" a magnetic field and rotation have on weather seems more like an allusion to an allusion than actually covering it. I'm not asking for a geo or astrophysics primer here, but you're not giving me much reason to consider the magnetic fields effect on Earths heat loss beyond the friction between it and the solar wind or a flare.
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

Yeah, I know the law, just hadn't stopped to think that Venus really is that much closer to the sun; my bad there. Whether or not I'm understanding the preceding properly, that alone should make an apple to apples comparison impossible. Of course, since water boils a long time before lead melts, it doesn't let us off the hook either. ;)
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.

Sure, but skepticism doesn't equal inaction, in fact, it actually means you hedge your bets, which is what taking steps to reduce our undeniably and dramatically increased CO2 emissions in the last two centuries would be. Setting that aside for the moment, however, I can think of several HUGE downsides to ignoring accurate predictions of significant warming:

First and foremost, I can walk from the Prime Meridian to the International Dateline a lot faster in Antartica than I can in Guatemala: The amount of tundra we'll reclaim is dwarfed by the amount of equatorial land that would become uninhabitable desert. In addition, not only do very few people live on that tundra now, but a LOT of people live in those equatorial regions. I don't think you'll be able to sell Brazil on global warming by telling them all to move to Canada (for that matter, it might make Canada a hard sell, too. ;)) That brings us to another problem: A disproportionate amount of the worlds population lives near the coast, and even more of it lives near SOME source of water, fresh or salt, and the best part is it's often the most impoverished and therefore least capable of adapting to drastic climate change. If the oceans rise and the Himalayas flood the Ganges India is in a very bad way, and the solution is not to move into the Himalayas; lukewarm barren rock is still barren rock. Until/unless equatorial temperatures reached the point where rainfall was rare, the monsoon rains resulting from the melting glaciers would be brutal as well. For coastal populations (which is a LOT of people) any sea level rise is dangerous, because water always finds its level: A sea level rise of just a few inches could permanently drive the shoreline 50 miles inland. The question isn't how much of FL is above sea level now, but how FAR, and for most of it the answer is "not very".

Then there's the ice caps. I try not to think about the ice caps, because they act like a natural thermostat, absorbing a great deal of heat when they melt, then accumulating frozen precipitation when temperatures drop. You know the drill: Until the ice melts it can't get above 0 centigrade, and it takes almost as much heat to accomplish that state change with NO temperature increase as it does to boil the water once it's melted. So long as there's snow on the ground here even the ambient temperature won't get more than a degree or two above freezing, and the ground will remain frozen throughout that time. Once the last of it's gone though there's nothing to absorb that heat in a state change: More energy means higher temperatures, period. Well, until we reach the point where all the water turns to steam, but one way or the other that won't be a problem for humans....

It really doesn't matter though. Whatever part of the current socio-economic system we look at that those running it have little incentive and thus little desire to change anything, so they'll continue to find reasons why they not only can but MUST do nothing. It doesn't matter that less waste and clean renewable energy are in everyones best interest, because cheap power is anathema to those who sell it for a living (cheap labor, OTOH.... ;)) That's why consumers will insist on poisoning, choking and roasting themselves BECAUSE IT COSTS THEM LESS. Once again, that's why businessmen whose only bottom line IS the bottom line accuse academics of greedy bias. It's like Lindsay Lohan ignoring her drug treatment counselor on the grounds that addicts can't be trusted. :rolleyes:

Love of money is the root of all evil, and if I pinned my hopes on Earth or any place visible from it I'd be very depressed. As it is I'm just debating how ethical reproduction is in a world where each generation is going to be increasingly screwed AND under increasing pressure to reject salvation.
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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 1022 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

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