4
$\begingroup$

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.

Improve this question
$\endgroup$

2 Answers 2

Reset to default
4
$\begingroup$

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.

Improve this answer
$\endgroup$
3
$\begingroup$

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?

Improve this answer
$\endgroup$
5
  • 1
    $\begingroup$ 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. $\endgroup$
    – f.thorpe ♦
    Commented Oct 8 at 1:55
  • 1
    $\begingroup$ 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. $\endgroup$
    – Rockdoctor
    Commented Oct 15 at 19:34
  • $\begingroup$ Thanks for correcting me, I was under the impression interhemispheric mixing was more in the 3-4 yr range. $\endgroup$
    – f.thorpe ♦
    Commented Oct 16 at 1:12
  • $\begingroup$ 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 !? $\endgroup$
    – Rockdoctor
    Commented Oct 16 at 10:31
  • $\begingroup$ "a matter of weeks on a national scale" -- not if you're Luxembourg! $\endgroup$
    – Wolfgang Bangerth
    Commented Oct 19 at 22:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.