From rmg3@access5.digex.net Fri Oct 3 15:04:22 EDT 1997
Article: 153150 of sci.environment
Path: digex!news2.digex.net!digex.net!not-for-mail
From: rmg3@access5.digex.net (Robert Grumbine)
Newsgroups: sci.environment
Subject: Re: NY Times on warming from the sun
Date: 3 Oct 1997 14:52:56 -0400
Organization: Under construction
Lines: 58
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References: <60dkh1$hh4$1@snipp.uninett.no> <60gj2t$5d3$1@snipp.uninett.no> <01bccc2f$96804850$e0baafce@hays> <60oqj3$e13$1@snipp.uninett.no>
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Xref: digex sci.environment:153150
Status: O
In article <60oqj3$e13$1@snipp.uninett.no>, Onar Aam wrote:
>
>You practically GIVE me ammunition here, Phil. How in the mother of God's
>name do you think that the oceans should get warmed up just a little bit.
>The oceans have a heat capacity that is approximately one million times
>larger than that of the entire atmosphere.
As with others, I wonder where you got that figure. But no matter,
I'm an oceanographer and like the idea of the ocean being so much more
important. Let's try to figure it out from general principles:
1) The specific heat of water is about 4000 J/kg/K, while that of
air is 1000 J/kg/K.
2) The density of water is about 1000 kg/m^3, while air is about 1 kg/m^3.
3) The average depth of the ocean is about 4000 meters, but ocean covers
only 70% of the earth, so equivalent depth is 2800 meters. I'll round
to 2500 since 4000 was too high (3730 is more accurate). The equivalent
depth of the atmosphere is 10,000 meters.
Combine:
specific heat ratio * density ratio * depth ratio = heat capacity ratio
4 * 1000 * 2.5/10 = 1000
So the ocean total heat capacity is about 1000, not a million, times
that of the atmosphere.
Of course, the heat is being added at the top of the ocean. Making
water warmer makes it less dense, so it tends to stay where it is.
The consequence is that you don't warm the whole ocean, you warm (to
first order) only the upper portion that is being mixed by the winds.
That's on the order of 50 meters, rather than 4000. Heat capacity
effect is now down to only a factor of 10-20.
Now let's go back to a fundamental matter that was lost earlier.
We've been talking so far about heat capacity, which is a measure of energy.
That's what the Joules (J) are about. Changes to climate do _not_
run on the basis of an energy input. Climate runs on _power_ --
energy _per unit time_, i.e. Watts. The solar constant is some
number of Watts, and the greenhouse effect (and human-enhance greenhouse
effect) increases the number of Watts of energy reaching the surface of the
earth (compared to the case of having no greenhouse effect; it doesn't
raise it over the solar constant).
By changing these wattages, the power delivery, we change the
heating or cooling _rates_ of the atmosphere and ocean. The factor
of 10-20 in heat capacity says that the ocean will warm only 5-10%
as fast as the atmosphere. So, in the time that the atmosphere warms
1 degree, we expect the upper ocean to warm about 0.05 to 0.1 degree.
There are other effects which have to be included, but since I'm
responding to a post that was off by a factor of 1000, this isn't
the time for it.
--
Robert Grumbine rmg3@access.digex.net
Sagredo (Galileo Galilei) "You present these recondite matters with too much
evidence and ease; this great facility makes them less appreciated than they
would be had they been presented in a more abstruse manner." Two New Sciences