<p>The simple answer is #1:</p>
<blockquote>
<ol>
<li>Greenhouse gases cannot remain concentrated in a region long enough to cause any local impacts, i.e., they diffuse too quickly ...</li>
</ol>
</blockquote>
<p>On the surface, it might seem like places with more unmixed GHG concentrations would be noticeably hotter.  However, that ignores the vertical nature of the atmosphere and that most absorption of infrared radiation from the Earth occurs far above where GHGs are locally concentrated (the surface of the Earth).</p>
<p>Furthermore, greenhouse gases are so potent because of their longevity in the atmosphere.  Tens, hundreds, and even thousands of years absorbing radiation again and again before being chemically converted or deposited.  This has climate impacts because the entire atmosphere is warming.  Temperature is generally driven by weather events, which are driven by much larger spatial scales. However, there are definite correlations to average temperature depending on land cover type (e.g. vegetation vs developed vs desert)</p>
<blockquote>
<p>...and the impact is global, not local.</p>
</blockquote>
<p>Whether it is &quot;global&quot; might be a bit more complex.  I would feel comfortable calling it &quot;hemispheric&quot;.  Typically it only takes a year or so for a GHG to get distributed evenly across a hemisphere.  It can take a bit longer to mix across the equator.</p>

CC BY-SA 4.0
2024-10-04T00:41:40.823Z
2024-10-16T01:07:31.773Z
2024-10-16T01:07:31.773Z
f.thorpe
<p>Reality has performed relevant experiments on a number of occasions. I don't think that anyone has <em>deliberately</em> performed such experiments, but you can argue that they have been done inadvertently.</p>
<p>Remember Mount Pinatubo erupting in the Philippines, in 1991? When it erupted it injected a few megatonnes (20-odd) of SO2 in the atmosphere, close to the equator. This was identifiable as a plume for several months, during which time it completed circling the Earth (the near-equatorial source was important in this). Over the next year or so, it disperses both north and south, and became dispersed into the general atmosphere.</p>
<p>Inadvertently, the nuclear Test Ban Treaty monitoring system performs (performed) similar experiments on an irregular basis. The detonation of a nuclear weapon releases short-lived and longer-lived isotopes of various elements into the atmosphere (even underground tests ; the detonation tends to make holes in containment structures), which disperse. Depending on the state of the weather and the size of the territory in which the explosion occurred, it can take several days for the plume to reach a detector, but invariably they do. (Embassies can have detector arrays on the roof ; not that the host country particularly likes this, but they don't want <strong>their</strong> embassies searched either.) Probably the best known exmaple of this was in tracking the nuclide plume form Chernobyl across eastern, then northern Europe in 1986.</p>
<p>Both of these types of data sources indicate that the diffusion and dispersal of point sources of gas in the atmosphere takes a matter of weeks on a national scale, and only a couple of years for a point emission to become globally mixed. The most persistent anomaly would be with a point source at high latitude, when it might take a half-decade or so to be dispersed into the opposite hemisphere.</p>
<blockquote>
<p>I hope I can learn if there are any models or measurements that show how narrow and/or quickly can effects of greenhouse gases be measured.</p>
</blockquote>
<p>Why look at models when you've got relevant experimental data?</p>

CC BY-SA 4.0
2024-10-08T01:55:02.607Z
Injecting aerosol into the stratosphere from a volcano is not the same thing as emitting GHGs at the surface of the Earth.  Very very different in fact.  GHGs from industrial activity does not get injected above the surface mixing layer in the troposphere, let alone the tropopause.  Thus, anything released at the surface takes a lot longer than 2 years to get globally mixed.
f.thorpe
CC BY-SA 4.0
2024-10-15T19:34:13.793Z
The annual cycles of increase/ decrease in CO2 levels in the Mauna Loa records suggest that the global mixing period is LESS than 2 years, probably less than 1 year.
To get into the stratosphere might take a couple of years, but the stratosphere (and above) is 90%+ of the volume of the atmosphere and a couple of percent by mass. Whichever you think is more important.
Rockdoctor
CC BY-SA 4.0
2024-10-16T01:12:23.583Z
Thanks for correcting me, I was under the impression interhemispheric mixing was more in the 3-4 yr range.
f.thorpe
CC BY-SA 4.0
2024-10-16T10:31:39.670Z
The Earth isn't a well-mixed lab flask. It isn't required to have "one" value for any particular parameter. Since Mauna Loa is, itself, to one side of the equator (I'd need a map - order of a couple of days sailing ; around a thousand km?), it's not purely going to estimate the interhemispheric mixing. Find an equally high volcano similarly placed south of the equator ... oh. How about funding for a labelled release experiment ? Funding !?
Rockdoctor
CC BY-SA 4.0
2024-10-19T22:30:35.623Z
"a matter of weeks on a national scale" -- not if you're Luxembourg!
Wolfgang Bangerth
CC BY-SA 4.0
2024-10-06T23:01:22.103Z
2024-10-06T23:01:22.103Z
Rockdoctor
<p>Suppose you have a point source of greenhouse gases. Does this lead to a locally higher concentration of gases, and if so does it lead to associated higher temperatures and other greenhouse effects? I'm imagining the extreme answers to be:</p>
<ol>
<li><p>Greenhouse gases cannot remain concentrated in a region long enough to cause any local impacts, i.e., they diffuse too quickly and the impact is global, not local. Or,</p>
</li>
<li><p>Greenhouse gasses can remain in concentrated in regions as small as xx km<sup>2</sup> and create substantially warmer microclimates in that region (I'm imagining something like a swamp).</p>
</li>
</ol>
<p>Of course, the answer might be somewhere in between. I'm obviously expecting this is a &quot;depends/it's complicated&quot; question, but I hope I can learn if there are any models or measurements that show how narrow and/or quickly can effects of greenhouse gases be measured.</p>

<climate><greenhouse-gases>
What is the spatial range of impact of abnormally high greenhouse gases?
jomurmiranda
# What is the spatial range of impact of abnormally high greenhouse gases?

(Asked by: username_0 on 2024-10-03)

Suppose you have a point source of greenhouse gases. Does this lead to a locally higher concentration of gases, and if so does it lead to associated higher temperatures and other greenhouse effects? I'm imagining the extreme answers to be:

1. Greenhouse gases cannot remain concentrated in a region long enough to cause any local impacts, i.e., they diffuse too quickly and the impact is global, not local. Or,
2. Greenhouse gasses can remain in concentrated in regions as small as xx km2 and create substantially warmer microclimates in that region (I'm imagining something like a swamp).

Of course, the answer might be somewhere in between. I'm obviously expecting this is a "depends/it's complicated" question, but I hope I can learn if there are any models or measurements that show how narrow and/or quickly can effects of greenhouse gases be measured.

**Tags:** climate, greenhouse-gases


---

## 2 answers

### Answer by username_1 on 2024-10-04. Score: 4 | Accepted answer

The simple answer is #1:

> 1. Greenhouse gases cannot remain concentrated in a region long enough to cause any local impacts, i.e., they diffuse too quickly ...

On the surface, it might seem like places with more unmixed GHG concentrations would be noticeably hotter. However, that ignores the vertical nature of the atmosphere and that most absorption of infrared radiation from the Earth occurs far above where GHGs are locally concentrated (the surface of the Earth).

Furthermore, greenhouse gases are so potent because of their longevity in the atmosphere. Tens, hundreds, and even thousands of years absorbing radiation again and again before being chemically converted or deposited. This has climate impacts because the entire atmosphere is warming. Temperature is generally driven by weather events, which are driven by much larger spatial scales. However, there are definite correlations to average temperature depending on land cover type (e.g. vegetation vs developed vs desert)

> ...and the impact is global, not local.

Whether it is "global" might be a bit more complex. I would feel comfortable calling it "hemispheric". Typically it only takes a year or so for a GHG to get distributed evenly across a hemisphere. It can take a bit longer to mix across the equator.


---

### Answer by username_2 on 2024-10-06. Score: 3

Reality has performed relevant experiments on a number of occasions. I don't think that anyone has *deliberately* performed such experiments, but you can argue that they have been done inadvertently.

Remember Mount Pinatubo erupting in the Philippines, in 1991? When it erupted it injected a few megatonnes (20-odd) of SO2 in the atmosphere, close to the equator. This was identifiable as a plume for several months, during which time it completed circling the Earth (the near-equatorial source was important in this). Over the next year or so, it disperses both north and south, and became dispersed into the general atmosphere.

Inadvertently, the nuclear Test Ban Treaty monitoring system performs (performed) similar experiments on an irregular basis. The detonation of a nuclear weapon releases short-lived and longer-lived isotopes of various elements into the atmosphere (even underground tests ; the detonation tends to make holes in containment structures), which disperse. Depending on the state of the weather and the size of the territory in which the explosion occurred, it can take several days for the plume to reach a detector, but invariably they do. (Embassies can have detector arrays on the roof ; not that the host country particularly likes this, but they don't want **their** embassies searched either.) Probably the best known exmaple of this was in tracking the nuclide plume form Chernobyl across eastern, then northern Europe in 1986.

Both of these types of data sources indicate that the diffusion and dispersal of point sources of gas in the atmosphere takes a matter of weeks on a national scale, and only a couple of years for a point emission to become globally mixed. The most persistent anomaly would be with a point source at high latitude, when it might take a half-decade or so to be dispersed into the opposite hemisphere.

> I hope I can learn if there are any models or measurements that show how narrow and/or quickly can effects of greenhouse gases be measured.

Why look at models when you've got relevant experimental data?

> **Comments:**
> **username_1**: Injecting aerosol into the stratosphere from a volcano is not the same thing as emitting GHGs at the surface of the Earth.  Very very different in fact.  GHGs from industrial activity does not get injected above the surface mixing layer in the troposphere, let alone the tropopause.  Thus, anything released at the surface takes a lot longer than 2 years to get globally mixed.  
> **username_2**: The annual cycles of increase/ decrease in CO2 levels in the Mauna Loa records suggest that the global mixing period is LESS than 2 years, probably less than 1 year. To get into the stratosphere might take a couple of years, but the stratosphere (and above) is 90%+ of the volume of the atmosphere and a couple of percent by mass. Whichever you think is more important.  
> **username_1**: Thanks for correcting me, I was under the impression interhemispheric mixing was more in the 3-4 yr range.  
> **username_2**: The Earth isn't a well-mixed lab flask. It isn't required to have "one" value for any particular parameter. Since Mauna Loa is, itself, to one side of the equator (I'd need a map - order of a couple of days sailing ; around a thousand km?), it's not purely going to estimate the interhemispheric mixing. Find an equally high volcano similarly placed south of the equator ... oh. How about funding for a labelled release experiment ? Funding !?  
> **username_3**: "a matter of weeks on a national scale" -- not if you're Luxembourg!  

---

