modest temp increase=irreversible loss of ice caps:

@metal-brain said
Variations in the Earth's orbit is just one of the Milankovitch cycles, but I have always been skeptical of that one. It doesn't seem like neighboring planets would have enough gravitational pull to change the Earth's orbit enough for that kind of change. Also, how do they know it happens every 100,000 years? That matches the ice age cycles perfectly, but did they find th ...[text shortened]... .025% is enough to cause a significant difference. It is actually absurd to assert that. Just silly.

Orbital predictions are a rather precise science, one uses perturbation theory. This was how they discovered Neptune. The degree of incident radiation is easily deduced using the inverse square law.

@deepthought said
Orbital predictions are a rather precise science, one uses perturbation theory. This was how they discovered Neptune. The degree of incident radiation is easily deduced using the inverse square law.

Yes, but is there a calculus prediction that appears to confirm an orbital change every 100,000 years? Then it must change back for the warming part of the cycle. How the heck does that happen?

Do you have any information explaining that?

@metal-brain said
NO!

You know fully well I have claimed methane is likely causing more AGW than CO2. How many farging times have we discussed it? Are you conveniently forgetting that???????

I created a whole bloody thread about it on this forum!!!!!

I know that but your concentration on CO2 made me think you perhaps forgot that bit.
But why do you dis CO2 as causing temp increases? We can do that in lab settings and it works out every time. What makes you think it is any different in Earth's atmosphere? Just a bigger lab.
But the methane problem is the elephant in the room and will get a whole lot worse the more average temperatures go up. Methane may go up ten times more than it is now and that will cause certain destruction to many life forms which we are already seeing with forms like coral and such and the acidifying of the oceans which WILL get a lot worse the higher those temps go up along with more severe hurricanes and the like.

@metal-brain said
Yes, but is there a calculus prediction that appears to confirm an orbital change every 100,000 years? Then it must change back for the warming part of the cycle. How the heck does that happen?

Do you have any information explaining that?

The Earth's orbit has a set of parameters that specify the ellipse that it follows. In the idealized two body problem the ellipse's parameters are all constants. In the perturbed case the parameters can change. Because the Sun is an oblate spheroid there is a correction term. So instead of:

V(r) = -GMm/r

We have

V(r) = - GMm(1/r + α( θ )/r^3 + ...)

where α( θ ) is a parameter that depends on the angle of the orbit relative to the line between the Sun's poles.

So the direction of the major axis is an angle we'll call φ = A, where A is constant. This then becomes φ = A + Bt, where B is calculated using perturbation theory. Because φ = φ + 2π, we have the major axis eventually returning to it's original direction.

The relevant orbital quantity for the 110 kyr cycle is the argument of periapsis ω (I suggest looking at the diagram on the eponymous Wikipedia page). This is the angle between the ascending node (when it crosses the Sun's equatorial plane) and perihelion (point of closest approach to the sun).

Perturbations are due to the Sun being an oblate spheroid, the other planets, and a tiny correction from General Relativity. The Earth's orbit has been calculated for the next billion years or so and they can measure the change in the argument of periapsis (or perihelion since it's an orbit about the Sun) and compare the results.

@metal-brain said
Yes, but is there a calculus prediction that appears to confirm an orbital change every 100,000 years? Then it must change back for the warming part of the cycle. How the heck does that happen?

Do you have any information explaining that?

Interesting, that 100K cycle. Here is a bit about long term patterns in Indonesia:

https://www.sciencedaily.com/releases/2014/03/140324154009.htm

I wonder where we are in terms of when the next ice cycle will begin? Are we in middle? I think the last ice age was 15 thousand years ago or so, does that mean we are not due for another 75,000 odd years or so?

@deepthought said
The Earth's orbit has a set of parameters that specify the ellipse that it follows. In the idealized two body problem the ellipse's parameters are all constants. In the perturbed case the parameters can change. Because the Sun is an oblate spheroid there is a correction term. So instead of:

V(r) = -GMm/r

We have

V(r) = - GMm(1/r + α( θ )/r^3 + ...)

where α ...[text shortened]... the argument of periapsis (or perihelion since it's an orbit about the Sun) and compare the results.

If there is no computer model to confirm the calculus of an altered Earth orbit it is still just a theory and nothing more.

I remember many years ago people made a big deal out of the planets all being on one side of the sun. There were predictions of chaos which never came true.

https://www.skyandtelescope.com/astronomy-resources/astronomy-questions-answers/will-there-ever-be-a-moment-when-all-eight-major-planets-are-in-a-straight-line-on-the-same-side-of-the-sun/

The orbit of planets are not aligned in a neat pattern though, so a 3D analysis of the orbits may lead to a closer alignment at certain times that a 2D based look would be inadequate to see the closest alignment possible. For this reason I am open to the possibility, but until a mathematical confirmation is shown I am still skeptical of planets so distant affecting our Earth's orbit.

I also do not see the sun's oblate shape to be significant enough to pull the earth into a different orbit even with the alignment of Venus, Mercury and our moon.

I think a 100,000 year solar cycle makes more sense.

@sonhouse said
Interesting, that 100K cycle. Here is a bit about long term patterns in Indonesia:

https://www.sciencedaily.com/releases/2014/03/140324154009.htm

I wonder where we are in terms of when the next ice cycle will begin? Are we in middle? I think the last ice age was 15 thousand years ago or so, does that mean we are not due for another 75,000 odd years or so?

We came out of an ice age relatively recently so we have plenty of time before the next one. One of the problems with trying to explain the Ice ages with changes in the Earth's orbit is how quickly the ice ages end. It is hard to imagine such a swift change in Earth's orbit to cause an ice age to end so quickly.

@metal-brain said
We came out of an ice age relatively recently so we have plenty of time before the next one. One of the problems with trying to explain the Ice ages with changes in the Earth's orbit is how quickly the ice ages end. It is hard to imagine such a swift change in Earth's orbit to cause an ice age to end so quickly.

Doesn't seem like that big a deal to me, if the temp goes up say 4 degrees C, things will happen fast.

@sonhouse said
Doesn't seem like that big a deal to me, if the temp goes up say 4 degrees C, things will happen fast.

The other planets do not have that much pull on the Earth, even with some aligned. I don't believe a calculus based computer model is capable of confirming such an effect because it is not possible.

The only way a significant change in Earth's orbit would be possible IMO is another planet on the other side of the sun with a similar orbit speed and distance around the sun. Theoretically it could be at an opposite elliptical orbit as earth and pass closely to earth while closer to the sun on one pass and farther away from the sun on the other pass. If it just so happens the other planet is on the other side of the sun right now we simply cannot see it, but how likely is that? Done laughing yet?

The concept would make a great science fiction movie though. It would allow for some far fetched fictional earth like planet with life on it on the other side of the sun. We could make up intelligent species that visited our earth when our planets were passing by affecting each other's orbit eccentricity. Then they had a nuclear war or a devastating ice age of their own.

Imagine the creative possibilities for science fiction. The 100,000 year solar cycle still seems more likely to me. It would conveniently explain the rapid change back to warming again.

@metal-brain said
If there is no computer model to confirm the calculus of an altered Earth orbit it is still just a theory and nothing more.

I remember many years ago people made a big deal out of the planets all being on one side of the sun. There were predictions of chaos which never came true.

https://www.skyandtelescope.com/astronomy-resources/astronomy-questions-answers/will-th ...[text shortened]... he alignment of Venus, Mercury and our moon.

I think a 100,000 year solar cycle makes more sense.

Predictions using calculus, I assume you mean hand calculation by this, are not compared with computer simulation to test their veracity. The results of calculations are compared with astronomical observation. That is the real test.

The calculations were originally done by hand. The advent of computers means that these calculations are now done on machines. The predictions are compared with astronomical observation. These are precision tests.

Let's focus on the orbital parameters of the Earth for now, we can deal with irradiance next. Do you dispute long term predictions of the Earth's orbit.

@deepthought said
Predictions using calculus, I assume you mean hand calculation by this, are not compared with computer simulation to test their veracity. The results of calculations are compared with astronomical observation. That is the real test.

The calculations were originally done by hand. The advent of computers means that these calculations are now done on machines. The pre ...[text shortened]... r now, we can deal with irradiance next. Do you dispute long term predictions of the Earth's orbit.

It doesn't seem like you know of any confirmation of the claim. I'm inclined to believe nobody has successfully done it. I doubt it can be done because I doubt the assertion is possible to any significant degree to cause an ice age. The planets are too far apart.

@metal-brain said
The other planets do not have that much pull on the Earth, even with some aligned. I don't believe a calculus based computer model is capable of confirming such an effect because it is not possible.

The only way a significant change in Earth's orbit would be possible IMO is another planet on the other side of the sun with a similar orbit speed and distance around the s ...[text shortened]... still seems more likely to me. It would conveniently explain the rapid change back to warming again.

What you insist on believing is somewhat irrelevant to this. At perihelion Jupiter is 4.9AU from the Sun. This means its closest approach to the Earth is 4AU. At aphelion it is 5.5AU from the Sun. I'll use 5AU as a convenient figure to get an estimate. Jupiter's mass is about 1/1000 that of the Sun's. This means that the force exerted by Jupiter at closest approach to the Earth is of the order of one part in 25,000th of that of the Sun. This is a significant perturbation.

Venus, at closest approach is about 0.3 AU from the Earth and has a mass of 1/412,000 of the Sun's. This produces a force of 1 part in 37,000 of that of the Sun.

This is enough to affect the Earth's orbit over these timescales.

@metal-brain said
It doesn't seem like you know of any confirmation of the claim. I'm inclined to believe nobody has successfully done it. I doubt it can be done because I doubt the assertion is possible to any significant degree to cause an ice age. The planets are too far apart.

See e.g.

https://en.m.wikipedia.org/wiki/VSOP_(planets)

For a description of one of the models. The aspidal precession of the orbit of Mercury is one of the tests of General Relativity.

You are clutching at straws.

@metal-brain said
The other planets do not have that much pull on the Earth, even with some aligned. I don't believe a calculus based computer model is capable of confirming such an effect because it is not possible.

The only way a significant change in Earth's orbit would be possible IMO is another planet on the other side of the sun with a similar orbit speed and distance around the s ...[text shortened]... still seems more likely to me. It would conveniently explain the rapid change back to warming again.

If there was a planet opposite the sun it would have been discovered long ago because of the perturbations of the orbits of the other planets.
That tired old hayseed theory has been rebuked ages ago. If an Earth sized body was actually in orbit 180 degrees out of our planet it would have been actually photographed by probes already, like voyager which took images of all the planets of the solar system in one image at one point and there was no planet 180 degrees out from Earth.

@deepthought said
What you insist on believing is somewhat irrelevant to this. At perihelion Jupiter is 4.9AU from the Sun. This means its closest approach to the Earth is 4AU. At aphelion it is 5.5AU from the Sun. I'll use 5AU as a convenient figure to get an estimate. Jupiter's mass is about 1/1000 that of the Sun's. This means that the force exerted by Jupiter at closest approach ...[text shortened]... t in 37,000 of that of the Sun.

This is enough to affect the Earth's orbit over these timescales.

Sure, but how much? I never said there wasn't an effect, just that it was insignificant to alter orbit enough to make much of a difference.