Global Cooling

[Dauphin]

quote: Stuff2 is partially right. One of the reasons sea level is expected to rise is due to the fact that warmer water takes up greater volume.

Depends on the average temperature. Water is at its densist at about 5C. If the average temperature is less than this then warming will decrease volume.

quote: normal pollution causing global warming and nuclear pollution causing nuclear winter...

Ozone depleting pollution is a third addition that should be made.

1. Nuclear - Nuclear winter - Global cooling
2. Greenhouse - Global warming - Raises sea level
3. CFCs etc - Causes dead tiles mainly near poles.

[Roman]

Big Crunch, average surface temperature is currently approximately 15 degrees Celsius and expected to rise by up to 5 degrees Celsius by the year 2100.
Water gets less dense when cooled below 4 degrees, because this is the point at which structure starts to appear in groups of water molecules hence destroying the tight packing of the molecules in an ordinary liquid.

[Dauphin]

quote: Big Crunch, average surface temperature is currently approximately 15 degrees Celsius and expected to rise by up to 5 degrees Celsius by the year 2100.

The surface water is only a tiny percentage of all the water. Whats the average temperature of the oceans as a whole?

[Roman]

I don't know the average temperature of all the oceans.
I can, however, assure you that it mmust be larger than 4 degrees Celsius. The reason for this is that just as you said water colder than 4 degrees is less dense than warmer water. This means such cold water would rise to the surface, but we know the surface temperature to be much higher than that.
Hence the temperature at the bottom of the ocean is at least 4 degrees Celsius and the average surface temperature 15 degrees Celsius. The temperatures in between vary within this temperature range. Obviously the average temperature of the ocean is therefore somwhere in between these two temperatures (probably closer to 4 rather than 15 degrees).
[This message has been edited by Roman (edited February 08, 2001).]

[Roman]

Nuclear war, an asteorite impact, or a volcanic eruption all have an initial cooling effect on the atmosphere, because they throw particulate matter into the atmosphere, which obscures the sun.

However, a volcanic eruption also releases a large amount of carbon dioxide into the atmosphere from the Earth's interior. Meanwhile, nuclear explosions and asteorite impacts generate intense heat at their points of impact leading to decomposition of carbon compounds and subsequent formation of carbon dioxide.

The result is that initial global cooling is followed ba a large increase in temperature due to global warming once the particulate matter settles.

[BRENNANonTHEmoor]

Good Idea to include nuclear Winter and Global Warming!

[Dauphin]

Roman, I see the logic and you are probably right that it is greater than 4C (but for other reasons.

However, by your logic the warm air at the Earths surface should rise to the top of the atmosphere - meaning its warmer near the top of Everest tahn at the bottom. Which it isn't.

The water at the surface is only warmer because heating takes place at the surface due to the sun. The amount of sunlight even a few hundred metres down is minimal. Its very cold.

Is this OT?

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Never argue with a fool; People might not know the difference

[Roman]

I see what you mean with the Mount Everest, but it doesn't quite work that way for four reasons.

1) Air at Mount Everest is much thinner and thus intercepts fewer infra-red rays from the sun than air at sea-level.

2) Air at sea level is also warmed from the Earth, which intercepts almost all infra-red radiation from the sun.

3) Higher atmosphere contains certain chemical
that act to cool it.

4) The primary greenhouse gas is carbon dioxide, which is a lot denser than air and hence tends to stay quite low in the atmosphere. It therefore traps the heat only in the lower portions of the atmosphere. Without carbon dioxide the lower sections of the atmosphere would be almost as cold as the outer atmosphere.

Of course the air rises from sea level upwards (this is what causes winds), but it has a much lower specific heat capacity than water, so it cools down relatively fast commpared to water.

[Roman]

quote: Originally posted by Big Crunch on 02-10-2001 07:17 AM The water at the surface is only warmer because heating takes place at the surface due to the sun. The amount of sunlight even a few hundred metres down is minimal. Its very cold.

Yes this is absolutely correct. However, it still doesn't stop water that is less dense than the surrounding water rising to the top, or equalising its temperature with the surroundings. In fact one of those two things must happen in the long term and both have the same effect of the least dense water being on the top and denser, 4 degree water on the bottom. It is dangerous to draw parallels with the atmosphere inn this case, due to the 4 special circumstances regarding Earth's atmosphere, I outlined above.

In fact I know this to be true with respect to lakes and seas. In all of these the temperature at the botom is 4 degrees, even in the arctic ocean. That is the reason why water freezes at the surface first and not at the bottom.

Yes, sunlight has trouble penetrating seawater due to the depth of the oceans. I agree that after say 1000 metres (this is a complete guess), the water temperature reaches 4 degrees, but after that it does not decrease any further. Precisely because I don't know where this point of thermal equilibrium is reached, I can't calculate for you the average temperature for the oceans as a whole.
It is also the reason why we can be completely certain that the average water temperature in the oceans is greater than 4 degrees Celsius.

[Roman]

Yes, this is probably OT.

[jdlessl]

One of the things that really pissed me off about SMAC was that you almost never had global cooling. You could blast an entire continent into the sky, which ordinarilly would block the sun for a couple years, but damned if sea levels didn't rise because of it.

If there are going to be weapons of mass destruction in Civ3, I certainly want to have to think about a nuclear winter.

--
Jared Lessl

[Dauphin]

quote: Of course the air rises from sea level upwards (this is what causes winds), but it has a much lower specific heat capacity than water, so it cools down relatively fast commpared to water.

Mainly due to adiabatic expansion from the reduced air pressure at higher altitudes. (I did an Atmospheric Physics module at university but not Oceanography).

quote: In fact I know this to be true with respect to lakes and seas. In all of these the temperature at the botom is 4 degrees, even in the arctic ocean. That is the reason why water freezes at the surface first and not at the bottom

I would guess that it is the higher pressures that prevents water from becoming ice at depths or under ice sheets. (Even if it is less than 0C). So I have doubts about this. I agree that if there is water at 4C it will most likely be at the bottom

I better say something on topic - The game should have global cooling in it.

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Never argue with a fool; People might not know the difference
[This message has been edited by Big Crunch (edited February 10, 2001).]

[Roman]

quote: Originally posted by Big Crunch on 02-10-2001 05:48 PM Mainly due to adiabatic expansion from the reduced air pressure at higher altitudes.

Correct indeed, I also did Physics.

quote: Originally posted by Big Crunch on 02-10-2001 05:48 PM I would guess that it is the higher pressures that prevents water from becoming ice at depths or under ice sheets. (Even if it is less than 0C).

This is not the case for two reasons.

1) The pressure of the water does not change by having an ice sheet on top any more than by having an equivalent (by weight) amount of extra water.

2) While pressure determines the boiling point of water, its effect on ice formation is only negligible.

Water in the oceans does not freeze even below 0 degrees Celsius, because it contains dissolved salts, which decrease its melting (freezing) point.

quote: Originally posted by Big Crunch on 02-10-2001 05:48 PM So I have doubts about this. I agree that if there is water at 4C it will most likely be at the bottom.

I can make this official now. This is exactly what happens, as I now looked it up. The water at the botom of the oceans is at 4 degrees Celsius.

I still have not managed to find out the total temperature of the oceans, though.


PS.
I think we have hijaked the thread by now for our intelectual discussion, but to comment on the game anyway, I would find it nice if global cooling was included, but by no means an essential feature of the game.