With all the concern about carbon in the atmosphere one may wonder what the future of coal may be.  To me, the ideal use of coal would be to use it to make carbon composite materials.  Carbon composites are noted to be stronger than steel by weight, and does not rot or rust.  With the carbon locked away in such construction material is cannot be a concern for the atmosphere.  The mining processes impacts then become the main concern.  With abundant energy, such as steam generating geothermal, such concerns may be much easier to address.

  If one looks at conditions likely occur in the future, science strongly suggests that there will come times when humanity will not be able to sustain itself on the surface of the planet due to various types of impacts from space.

  One obvious situation is the normal glacial-interglacial cycle.  In the past, thick ice sheets covered the land as far south as Nebraska, as I remember the information.

  Another is the magnetic field periodically getting weak.  This allows solar radiation to penetrate the atmosphere which then can damage body tissue.  They say our magnetic field is on the wane.  Eventually it will come back with the field polarity reversed.  In waned period, there will be numerous weak magnetic poles moving around; which then will even draw the already relatively uninhibited solar radiation to land on those areas.

  A major one, recently discovered, is the cycle of the orbit of our solar system in the galaxy.  That orbit periodically brings us nears the edge of the galaxy, the intergalactic wind of charged particle then can reach earth's surface.  Since this wind comes from one part of the sky, one may only need to seek cover about half of the day.  Plants stuck in on the surface would likely be damaged also.  As one passes through the year, the time of day of concern would slowly shift around.  In one part of the year it would be at night, and later the radiation would show up in the morning, and so on.  Taking a whole year to cycle through the part of day effected the most by the radiation.

  And there are others.  Such as a star which becoming a super nova being close enough earth and having its rotatiing poles oriented so that it points in our direction can send a deadly beam (of gamma rays, I believe) at us.  (If you think orientation may be a very limiting factor; consider the fact that numerous planets have already been discovered obiting stars.  That detection process usually takes having the star's planet orbiting in a thin line between us and that star.  Those particular stars will not likely ever be a concern.  Yet it shows that such a very precise alignment can occur more frequently that one might suspect.  There are a lot of stars out there.)

  That said, it seems clear to me that having sustainable ways to survive under ground would be a serious help for mankind in the future.

  For what ever it's worth, there is a prediction by an Indian visionary that said:  When every thing here (I presume the white man's buildings, though it may have included the biology, or even more) was 30 feet under ground they would get their land back.  One presumes the buffalo would also be back in the mix if the Indian had it their way.  How animals learned to survive past cycles; I cannot say, unless canyons wall were noted as helping a nauseated stomach [or other symptom(s) caused by radiation].  Who can say...

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