Re: Democratic candidates address the issue of global warming while Republicans snooze...

On Fri, 4 Jan 2008, Rumpelstiltskin wrote:

On Fri, 04 Jan 2008 01:18:27 GMT, Rumpelstiltskin
<PleaseDoNotReplyByEmail@xxxxxxxxxxx> wrote:

On Fri, 04 Jan 2008 01:07:27 GMT, Rumpelstiltskin
<PleaseDoNotReplyByEmail@xxxxxxxxxxx> wrote:

<snip>


I agree the effect is not very significant. The
eccentricity of Earth's orbit is one part in 60, so
the difference in luminosity from the sun between
apogee and perigee is 1.016 squared or about
1.032, three percent. More important, I'd say,
though still not very important, is the fact that the
Earth is moving more slowly at aphelion which
occurs in early July, when the Southern
hemisphere is in its winter, so the Southern
hemisphere winters are slightly longer than the
Northern, I guess by the same three percent
since that ratio is also a square. See the cute
moving illustration at:
http://tinyurl.com/2fzt4y



I think I screwed up the calculation. The article
at the URL above says the earth is 3.2% farther
from the sun at aphelion and at perihelion. Maybe
the eccentricity works on both sides, so that the
earth is BOTH 1/60 closer than a circle to the sun
at perihelion AND 1/60 further away than a circle
at aphelion. In that case, the difference in
luminosity would be 6% instead of 3%, and also
the difference in the length of winter would be 6%.
That's a bit more significant.



That is indeed the case. See the geometry
of ellipses, noting the position of a focus with
respect to the closest and furthest distances
to the path of the elliptical orbit, at:
http://tinyurl.com/357se4
You do have to both add the distance determined
by the eccentricity number from the perihelion
distance and also add it to the aphelion distance.
(The sun is at one focus of a planet's elliptical orbit.
Take your pick which focus, it doesn't matter.)

Here you assume that the difference in the orbit is significant-- ie more than the effect of changes in the earth's tilt. Problem with this reasoning is that no one has noticed a change in the average over a year of the solar constant. Ie the average energy from the sun remains the same from year to year. Picking the average out of a signal with so much noise is hard but IIRC over a century of efforts and with recent independent satellite data finally coming into agreement, I would think that this issue is closed.

Even with the tilt change, I can see that a new section at the poles become cooler, but that just means that the previous cool spot before the change becomes warmer. The exchange of total energy still remains the same on the average. This is why I think that change which is observed from changes in tilt must be secondary or of the order (1/60)**2. With so small a result, it would be prudent to wait and see if someone else can independently come up with the same number.
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