<p>The difference is that your analysis is assuming that the albedo stays fixed, so the surface temperature simply scales like luminosity to the 1/4 power.  The Wiki entry is including feedback from the greenhouse effect, which will tend to further increase the surface temperature.  Note that an analysis that just looks at solar irradiation would get way too low a surface temperature for Venus, for example.  I can't speak to the accuracy of the feedback included-- as I understand it, that is far from a simple effect to include.</p>

CC BY-SA 4.0
2019-03-26T02:49:28.497Z
2019-03-26T02:49:28.497Z
Ken G
<p>We know that presently Sun is 4.5 billion years into its main sequence. It has another 5 billion years before it enters the Red Giant phase. We also know that Sun's luminosity increases by 10% every billion years during the main sequence. I am interested in finding the temperature rise as we approach the end of main sequence. I got two different values for temperature on Earth. </p>

<p><a href="https://en.wikipedia.org/wiki/Future_of_Earth#Loss_of_oceans" rel="nofollow noreferrer">Wikipedia</a> entry says that temperature on Earth would be 422 k in 2.8 billion years. However, if we use the formula for effective temperature as discussed in this answer 
<a href="https://earthscience.stackexchange.com/a/4274/15299">https://earthscience.stackexchange.com/a/4274/15299</a> and L = 1.8 then, the temperature on Earth would be 330K. Also in <a href="https://www.springer.com/us/book/9783319649603" rel="nofollow noreferrer">this book</a>, the author does the same calculations on page 255. </p>

<earth><main-sequence><red-giant><hypothetical>
What will be the temperature on Earth when Sun finishes its main sequence?
sidharth chhabra
# What will be the temperature on Earth when Sun finishes its main sequence?

(Asked by: username_0 on 2019-03-26)

We know that presently Sun is 4.5 billion years into its main sequence. It has another 5 billion years before it enters the Red Giant phase. We also know that Sun's luminosity increases by 10% every billion years during the main sequence. I am interested in finding the temperature rise as we approach the end of main sequence. I got two different values for temperature on Earth.

[Wikipedia](https://en.wikipedia.org/wiki/Future_of_Earth#Loss_of_oceans) entry says that temperature on Earth would be 422 k in 2.8 billion years. However, if we use the formula for effective temperature as discussed in this answer
<https://earthscience.stackexchange.com/a/4274/15299> and L = 1.8 then, the temperature on Earth would be 330K. Also in [this book](https://www.springer.com/us/book/9783319649603), the author does the same calculations on page 255.

**Tags:** earth, main-sequence, red-giant, hypothetical


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## 1 answers

### Answer by username_1 on 2019-03-26. Score: 6 | Accepted answer

The difference is that your analysis is assuming that the albedo stays fixed, so the surface temperature simply scales like luminosity to the 1/4 power. The Wiki entry is including feedback from the greenhouse effect, which will tend to further increase the surface temperature. Note that an analysis that just looks at solar irradiation would get way too low a surface temperature for Venus, for example. I can't speak to the accuracy of the feedback included-- as I understand it, that is far from a simple effect to include.


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