Re: Detecting ETI via CO2

Wasn't it Bjorn Damm who wrote:
>"Rob Dekker" <rob@xxxxxxxxxxx> skrev i meddelandet
>news:68JDe.1532$Fk4.146@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
>> With the increasing success of detecting planets around other star
>> systems,
>> the time is near that we will detect the first Earth-like planets (if they
>> are there) orbiting stars other than the sun.
>>
>> If, and when we do so, I'm sure that scientists will go the next step, to
>> analyze these planets' atmospheric composition and attempt to find oxygen
>> and water.
>> With increased sensitivity and prolonged observation, they might even find
>> rather accurate readings for gases like CO2 and methane.
>>
>> Now suppose that an ETI out in the Galaxy has found Earth and observed it
>> for hundreds of years. They know our atmosphere's composition pretty
>> accurately.
>> It might be possible that they have noticed a rapid increase of CO2 in our
>> atmosphere (from about 275ppm a few centuries ago, to almost 400ppm now).
>> Similar steep increase should be noticable for methane.
>>
>> This should seem like a very uncommon, and artificial, increase in
>> atmospheric composition, since natural effects of changes in atmospheric
>> composition are much, much slower than that.
>> The ETI could thus conclude that there is probably an emerging technology
>> on
>> our planet, burning massive amounts of fossil fuels....
>>
>> Is this a possible scenario ?
>> Can CO2 levels in our atmosphere be observed by ETI's ?
>> If so, what kind of equipment would they need ?
>> And can a rapid increase in CO2 (30% - 50% increase in 100 years) be
>> explained as natural effects (such as massive change in vulcanic activity)
>> ?
>> It surely did not change so fast in the past million years or so...
>>
>> Could rapid changes in extra-solar planet atmospheric conditions be an
>> indication of ETI ?
>> And are there maybe other rapid changes (such as global warning) caused by
>> activity of emerging technology civilizations burning fossil fuels, that
>> could be observed from interstellar distances ?
>
>Global warming can have natural causes. If, during an ice age, the planet
>becomes slightly warmer the ice starts to melt making the planet darker and
>thereby warmer, melting more ice, making the planet even more warmer ... and
>you have a runaway climat change, without any help from ET.
>
>There is a large amount of CO2 in the oceans. If it is realeased the amount
>in the atmosphere would increase.
>
>A collision with another object could probaby cause a rapid change in the
>atmosphere of the planet.

Plate tectonic movements can cause natural climate changes that cause
vast forests to become deserts. All the carbon locked up in those trees
has to go somewhere. That would be somewhat slower that the man-made
rise in CO2, but might be in a feasible range for a civilization that
wasn't quite so reckless with its planetary resources.

Supervolcanoes can cause drastic changes in the atmosphere, but that
would be too fast. However, there might be volcanic events on other
planets that are slower than supervolcanoes (like Yosemite) but faster
than bigger events like the Dekkan Traps.


Note also, that an artificial rise in CO2 probably only ever happens
once in the lifetime of a planet. If the inhabitants survive the effect
without using up all the planet's fossil fuel reserves, they probably
learn how to avoid repeating the effect. So you're looking for an effect
that lasts a century or two in a planetary lifetime of many billions of
years.

--
Mike Williams
Gentleman of Leisure
.

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