Sun's expansion GW factor at all?

[Zablorg]

I had heard someone talking a day or two ago about the expansion of the sun, and how it accounts for the climate change of the Earth. Now, I am quite certain this is an exaggeration, but it's the kind of stuff that keeps me up at night; how much does the sun's expansion affect the Earth's climate change? Does it even affect it at all?

[Darth Yoshi]

The sun's expansion doesn't happen on a timescale even remotely approaching the current climate crisis. Moreover, I believe that the sun will actually during the final stages of its existence, although I will readily admit that I'm likely wrong about that.

[SpacedTeddyBear]

I had heard someone talking a day or two ago about the expansion of the sun, and how it accounts for the climate change of the Earth. Now, I am quite certain this is an exaggeration, but it's the kind of stuff that keeps me up at night; how much does the sun's expansion affect the Earth's climate change? Does it even affect it at all?

The day that the expansion of the sun accounts for climate change, the Earth would be in the Sun's corona. Of course that is in another few billion years.

[Alyrium Denryle]

I had heard someone talking a day or two ago about the expansion of the sun, and how it accounts for the climate change of the Earth. Now, I am quite certain this is an exaggeration, but it's the kind of stuff that keeps me up at night; how much does the sun's expansion affect the Earth's climate change? Does it even affect it at all?

Already accounted for in the terrifyingly complex climate models

[Guardsman Bass]

It does, and there is some effect with the sunspot cycle, but as AD pointed out above, it has already been taken into account. However, the Sun's expansion, specifically, only matters on a scale of hundreds of millions or billions of years (I've read that the Sun is slowly increasing in luminosity, and in a billion years or so it will become luminous enough to render Earth uninhabitable in its current position).

[starslayer]

I don't know about the Sun's expansion, incremental as it may be (link to an explanation of this? and not the red giant stage), the Sun is steadily increasing in luminosity, and this will render Earth uninhabitable in anywhere from 200 million to 2 billion years. However, this has no effect on present climate, because there is already a feedback mechanism in place that deals with this by just as steadily removing carbon dioxide from the atmosphere and storing it in carbonate rocks, IIRC. The problems come first when there's too little carbon dioxide for plants to function, and then again when it's all removed, and the Earth really starts to heat up out of control, killing all life and turning the planet into another Venus.

[Guardsman Bass]

I don't know about the Sun's expansion, incremental as it may be (link to an explanation of this? and not the red giant stage), the Sun is steadily increasing in luminosity, and this will render Earth uninhabitable in anywhere from 200 million to 2 billion years. However, this has no effect on present climate, because there is already a feedback mechanism in place that deals with this by just as steadily removing carbon dioxide from the atmosphere and storing it in carbonate rocks, IIRC. The problems come first when there's too little carbon dioxide for plants to function, and then again when it's all removed, and the Earth really starts to heat up out of control, killing all life and turning the planet into another Venus.

You could still presumably have functioning sea biospheres for a lot longer after the air content of CO2 has plummeted, but you will eventually hit a point where it starts breaking down and/or evaporating the oceans.

[Count Dooku]

As the Sun expands, it gets cooler. So the sole fact that it is expanding does not necessarily mean it's going to affect us now. As others have said, timescale is a big problem in the expanding Sun argument.

[Korto]

As the Sun expands, it gets cooler. So the sole fact that it is expanding does not necessarily mean it's going to affect us now. As others have said, timescale is a big problem in the expanding Sun argument.

I believe the reason a star expands is because it's putting more energy out, and the extra energy causes the surface to puff out further. The reason the surface is then cooler is because there's so much more surface, despite giving out more energy, it's giving out less per unit area.
Although, yeah, long time to go before all that yet.

[Wyrm]

Zablorg, ask your friend how he got the figures for how much the sun is expanding. Because Brown & Christensen-Dalsgaard (1998) carried out a detailed study of the solar radius over the course of six years, during which time the solar radius remained constant within an error of ±37 km. Over the course of fifty years, this would account for an expansion in radius of no more than one part in 4514. This means that the solar disk (and therefore solar output) has expanded by only 4.122e-6 times. This is utterly negligible.

[The Duchess of Zeon]

Also, the expansion of the sun would really only have a very minor effect on warming, since the size of the Earth is unchanged, and thus our area for absorbing energy is the same--and btw, suns expand as they cool.

Anyway, only 1/3rd of the recent, sharp global warming can be accounted for by natural sources; the other 2/3rds is manmade.

[starslayer]

and btw, suns expand as they cool.

You've got it backwards, Duchess. As stars expand, they cool off for the reason Korto gave. Also, if the size of the solar disk increases, the amount of radiation reaching the Earth does indeed increase, assuming a constant irradiance, simply because the Sun is putting out more radiation in our direction, and the radiating surface is now just a little bit closer than it was before, decreasing the amount of attenuation in irradiance caused by the inverse-square nature of light propagation. Anyways, as has already been noted, none of this will be significant for hundreds of millions to billions of years.

[Fingolfin_Noldor]

The issue with the sun radius will be a serious problem when the hellium burn starts. By then, you probably have the Sun right at our door step.

I believe the simpler way of explaining the issue is that the sun has many layers of fusion, with the fusion taking place around the core requiring the most amount of gravity for containment. As you work outwards, you have the fusion processes that require less gravity for containment. (partly the heavier elements sink to the depths of the star) Now when the star expands, it just means that the fusion is growing hotter and work is being done against the gravitational force. Of course, this means more energy is being emitted though. But going by the figures Wyrm provided, we shouldn't see much by way of a change over the span of the years given.

[The Duchess of Zeon]

and btw, suns expand as they cool.

You've got it backwards, Duchess. As stars expand, they cool off for the reason Korto gave. Also, if the size of the solar disk increases, the amount of radiation reaching the Earth does indeed increase, assuming a constant irradiance, simply because the Sun is putting out more radiation in our direction, and the radiating surface is now just a little bit closer than it was before, decreasing the amount of attenuation in irradiance caused by the inverse-square nature of light propagation. Anyways, as has already been noted, none of this will be significant for hundreds of millions to billions of years.

Yeah, I'm aware, but I think I was trying to imply that the two would balance each other out, at least for quite some time.

[Darth Wong]

It's easier to just point out that there is no significant solar expansion or increase in luminosity whatsoever on human timescales, and that people who claim otherwise are simply lying.

[Darth Raptor]

The issue with the sun radius will be a serious problem when the hellium burn starts. By then, you probably have the Sun right at our door step.

Won't the orbits of the inner planets be pushed outward as the sun expands?

[Wyrm]

Won't the orbits of the inner planets be pushed outward as the sun expands?

Why? It's not as if the planetary orbits are rigidly attached to the sun's surface.

[starslayer]

Won't the orbits of the inner planets be pushed outward as the sun expands?

The planets' orbits will get bigger as the Sun ages, but not because the Sun is expanding; Since the Sun is roughly spherical, it can be treated as a point mass in determining its gravitational field for all points outside it, like the planets. However, the Sun is losing mass through the solar wind and through its own nuclear reactions, and this is what causes the planets to drift further out. Again though, this effect, like the increase in solar luminosity as it ages, is so slow as to be totally insignificant over the entire course of recorded history, much less the several hundred years we care about.