<p>If you could detect/isolate the infrared signal coming from the Earth - then yes, it would be obvious over decadal timescales. The amount of CO2 in the Earth's atmosphere has increased by about 25% since 1960 (<a href="https://climate.nasa.gov/vital-signs/carbon-dioxide" rel="noreferrer">https://climate.nasa.gov/vital-signs/carbon-dioxide</a>).</p>
<p>All you would have to do is focus on an unsaturated absorption feature attributable to CO2 and watch it grow with time.</p>
<p>In practice, the analysis would be more complex and you would fit an atmospheric model to the entire spectrum and all its features.</p>
<p>The problem is that the first <em>if</em> of this answer is a big if. There is no immediate prospect of being able to do this for Earth-like planets orbiting sun-like stars at a distance of 1 au. The telescopes we have are not sensitive enough and there is not enough spatial resoluton to achieve the necessary contrast between the star and the planet, in order to isolate the spectrum from the tiny planet against the &quot;glare&quot; of the star.</p>
<p>Maybe there is a chance for Earth-sized planets that are orbiting very close to extremely low-mass stars or brown dwarfs. I believe JWST is trying to make those measurements but it is still extremely challenging at distances of tens of parsecs to the nearest examples.</p>

CC BY-SA 4.0
2024-10-04T16:04:06.057Z
"There is no immediate prospect of being able to do this for Earth-like planets orbiting sun-like stars at a distance of 1 au." Is this true even when the planet occults its star?  I recall reading that occultation allows studying the planet's atmosphere because some light from the star passes through the atmosphere.
Ryan_L
CC BY-SA 4.0
2024-10-04T16:09:21.893Z
@Ryan_L such studies are not possible for Earth-like planets orbiting sun-like stars at 1 au. I believe they are mostly being done on giant hot Jupiters.
ProfRob
CC BY-SA 4.0
2024-10-04T19:19:42.393Z
At 1 au earth sized planets do not have a large enough relative size to occlude their star.
Questor
CC BY-SA 4.0
2024-10-04T22:39:04.763Z
@Questor it makes no difference how far the planet is from the star other than making the transits more unlikely and less frequent. The transit amplitude is unchanged with distance.
ProfRob
CC BY-SA 4.0
2024-10-04T22:50:59.817Z
Yeah, you are right... I was thinking of placing a rogue earth sized planetoid could occlude a star if it was the right distance between us and said star. And that doesn't really count as orbiting said star anymore. Would cause some excitement though
Questor
CC BY-SA 4.0
2024-10-05T17:36:26.360Z
While the CO2 concentration in the atmosphere went up by 25% relative to the level in 1960, its absolute concentration is around 400 ppm or 0.04%. Could one actually detect such a large relative change for so small absolute concentrations?
quarague
CC BY-SA 4.0
2024-10-05T18:07:22.700Z
@quarague the absolute concentration doesn't matter. The trace of CO2 has profound consequences for IR absorption.  Lithium has a concentration of <0.0000001% in stellar atmospheres and I've spent a career studying it. Unsaturated absorption lines increase linearly with abundance.
ProfRob
CC BY-SA 4.0
2024-10-07T19:41:14.090Z
@ProfRob How good are we now at estimating age by lithium content?
Jack R. Woods
CC BY-SA 4.0
2024-10-07T20:06:31.413Z
@JackR.Woods https://ui.adsabs.harvard.edu/abs/2023MNRAS.523..802J/abstract https://ui.adsabs.harvard.edu/abs/2024MNRAS.tmp.2100W/abstract
ProfRob
CC BY-SA 4.0
2024-10-09T22:50:43.800Z
@ProfRob Thank-you. Primary on this one! Thank you for still talking to us mere mortals!
Jack R. Woods
CC BY-SA 4.0
2024-10-04T09:14:00.973Z
2024-10-04T09:14:00.973Z
ProfRob
<p>Since we can determine atmosphere composition of exoplanets using spectroscopy, would a satellite pointed at Earth be able to do so and have enough detail to detect increasing CO2 levels? (Assuming that the satellite is close enough to Earth- say, less than 50 LY- and has been looking at earth for long enough to be able to see significant changes) I know we have earth-orbiting satellites like TEMPO which can detect pollution among other things, but I'm curious if a satellite significantly outside the solar system could see this (and, likewise, if we could see exoplanets going through this kind of change).</p>
<p>Are there any hard limits on this- size of satellite, distance, etc.?</p>

<exoplanet><spectroscopy><climate>
Would a satellite outside of the solar system be able to detect climate change/CO2 increases via spectroscopy?
aqua
# Would a satellite outside of the solar system be able to detect climate change/CO2 increases via spectroscopy?

(Asked by: username_0 on 2024-10-04)

Since we can determine atmosphere composition of exoplanets using spectroscopy, would a satellite pointed at Earth be able to do so and have enough detail to detect increasing CO2 levels? (Assuming that the satellite is close enough to Earth- say, less than 50 LY- and has been looking at earth for long enough to be able to see significant changes) I know we have earth-orbiting satellites like TEMPO which can detect pollution among other things, but I'm curious if a satellite significantly outside the solar system could see this (and, likewise, if we could see exoplanets going through this kind of change).

Are there any hard limits on this- size of satellite, distance, etc.?

**Tags:** exoplanet, spectroscopy, climate


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## 1 answers

### Answer by username_1 on 2024-10-04. Score: 10 | Accepted answer

If you could detect/isolate the infrared signal coming from the Earth - then yes, it would be obvious over decadal timescales. The amount of CO2 in the Earth's atmosphere has increased by about 25% since 1960 (<https://climate.nasa.gov/vital-signs/carbon-dioxide>).

All you would have to do is focus on an unsaturated absorption feature attributable to CO2 and watch it grow with time.

In practice, the analysis would be more complex and you would fit an atmospheric model to the entire spectrum and all its features.

The problem is that the first *if* of this answer is a big if. There is no immediate prospect of being able to do this for Earth-like planets orbiting sun-like stars at a distance of 1 au. The telescopes we have are not sensitive enough and there is not enough spatial resoluton to achieve the necessary contrast between the star and the planet, in order to isolate the spectrum from the tiny planet against the "glare" of the star.

Maybe there is a chance for Earth-sized planets that are orbiting very close to extremely low-mass stars or brown dwarfs. I believe JWST is trying to make those measurements but it is still extremely challenging at distances of tens of parsecs to the nearest examples.

> **Comments:**
> **username_2**: "There is no immediate prospect of being able to do this for Earth-like planets orbiting sun-like stars at a distance of 1 au." Is this true even when the planet occults its star?  I recall reading that occultation allows studying the planet's atmosphere because some light from the star passes through the atmosphere.  
> **username_1**: @username_2 such studies are not possible for Earth-like planets orbiting sun-like stars at 1 au. I believe they are mostly being done on giant hot Jupiters.  
> **username_3**: At 1 au earth sized planets do not have a large enough relative size to occlude their star.  
> **username_1**: @username_3 it makes no difference how far the planet is from the star other than making the transits more unlikely and less frequent. The transit amplitude is unchanged with distance.  
> **username_3**: Yeah, you are right... I was thinking of placing a rogue earth sized planetoid could occlude a star if it was the right distance between us and said star. And that doesn't really count as orbiting said star anymore. Would cause some excitement though  
> **username_4**: While the CO2 concentration in the atmosphere went up by 25% relative to the level in 1960, its absolute concentration is around 400 ppm or 0.04%. Could one actually detect such a large relative change for so small absolute concentrations?  
> **username_1**: @username_4 the absolute concentration doesn't matter. The trace of CO2 has profound consequences for IR absorption.  Lithium has a concentration of <0.0000001% in stellar atmospheres and I've spent a career studying it. Unsaturated absorption lines increase linearly with abundance.  
> **username_5**: @username_1 How good are we now at estimating age by lithium content?  
> **username_1**: @JackR.username_5 https://ui.adsabs.harvard.edu/abs/2023MNRAS.523..802J/abstract https://ui.adsabs.harvard.edu/abs/2024MNRAS.tmp.2100W/abstract  
> **username_5**: @username_1 Thank-you. Primary on this one! Thank you for still talking to us mere mortals!  

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