Many people have argued that as long as humans live only on Earth, we have
"all our eggs in one basket". They suggest we need space
colonies to insure the future of the species.
There are many current and potential threats to the human race. However,
considering the human source of many of the threats and the time-scales
involved, I'm not sure that space colonization should be the top priority in
preempting those threats.
Timescales
To consider how well space colonization is likely to solve our problems we need
to ask what the time-scales of sustainable, independent space colonies
are. If, after disaster strikes Earth, Earth is still able to supplement
the needs of space colonies, then those space colonies aren't necessarily
essential to continuing the human race. We have to ask when space
colonies would be functioning without need of any assistance from Earth.
Truly independent space colonies must not simply provide bare nutrition, air,
heat, and habitat repair for 100 years. They should have a
non-traumatizing environment with enough people to protect against dangerous
levels of inbreeding – able to last and progress indefinitely. There will
also be a minimum number of people required for any space colony in order to
provide needed manpower in various occupations (one person with multiple
occupations doesn’t help if you need two of those occupations in different
places at the same time).
How does that compare to the time-scales of threats from climate change,
environmental crisis, nuclear / bio weapons and accidents, possible nanotech
weapons or accidents, overpopulation, etc.? We also have to consider
threats to the global economy, since an economic collapse would presumably at
least interrupt efforts towards establishing space colonies. Economic
crises also increase risks of war, which could have apocalyptic consequences.
Even assuming the ultimate solution of human survival is space colonization, we
may need to find a way to extend the lifespan of human civilization and economy
on Earth in order to have time to accomplish sustainable space colonization.
Consider the possible habitats. Space stations in orbit around Earth or
at L5 have little natural resources at their location other than solar
energy. The Moon has no atmosphere, a limited amount of water at best,
which part of the Moon has access to solar energy varies during the month, and
it's not considered one of the solar system's better sources of minerals.
Venus is extremely hot, the atmosphere is dangerous and with the cloud cover
I'm not sure how practical solar energy would be at the surface. Mars has
too little atmosphere and accessible water is questionable, etc. Some of
the outer planets' moons may have enough ice and raw materials, but are very
cold, lack usable atmospheres and get limited solar energy. And so on.
We may be able to establish bases at some of these places in a realistically
short amount of time, but not independent ones. Any colony that
wants to get resources from post-apocalyptic Earth will need to have spaceships
that can land on Earth and later achieve escape velocity from Earth while
carrying cargo without help from Earth. Otherwise, the needed resources
may not be available from a single astronomical body. That could require
longer-distance travel between bodies - whether that's between asteroids,
between moons, between planets or some other combination. Significant
space travel ability may be essential. A colony would need an industrial
base capable of extracting and refining raw materials, and making useful things
from them.
Interstellar colonies and terraforming of planets in our solar system are
longer-range goals. Colonies in any place other than an Earth-like planet
will require a substantial infrastructure to allow humans to exist in an
otherwise deadly environment. The colony needs to be able to maintain and
repair that infrastructure...
There is a significant difference between an enormous disaster on Earth and one
at any space colony we can expect for at least a century. Even something on
the scale of a "dinosaur killer" asteroid impact won't necessarily
kill all humans on Earth. (However, if the world economy / technology is
set back too much it may not be possible to re-achieve a hi-tech civilization.
We've extracted most minerals / fossil fuels that can be gotten without
hi-tech, a post-disaster society may be left unable to get these.) It will be
a long time before an independent space colony could grow to the point some of
its people could survive after a major disaster.
Meanwhile, we have not yet solved the physical and psychological problems that develop
during months of low gravity. Most of the physical issues may not be
significant for those who never intend to return to Earth-type gravities.
Psychological issues remain. Some physical issues may arise when dealing
with years and decades in low gravity. Even in shorter spans of time,
weakening bones may have serious consequences in low gravity situations.
Weakened hip bones may be a problem for women giving birth in low
gravity. Other stressful activities may also be problematic. We
need to find out how low gravity will effect a fetus during pregnancy and child
growth afterwards. Identifying and resolving all the issues is likely to
take many years.
Currently, our society is not inclined to invest that much in either stopping
global warming (and other threats) or space habitats. It strikes me as
improbable that we will see a heavy investment in both of them at the same time
in the next period of time. My impression is the best chance for human
survival is focusing as much as possible on one or the other of the two paths,
and that space colonization will not solve the problem within the limited
time-frame.
Of course, if governments refuse to fund solutions to the environmental crisis,
but budget money for space habitats we should use that money. Hopefully,
governments will respond to the crisis before it’s too late and the problems
will be brought under control and within safe limits. Then there will be
no reason not to expand out into the universe.
Postscript
For those who still believe space colonization should be the priority, I would
like to suggest one piece of advice. The known threats to human survival
in the next century or so are not vast earthquakes and volcanoes, asteroid
impacts, supernovas or other natural disasters. Most of them are at least
partly man-made. If the same problems are not to threaten survival of
humans on space colonies, we either have to make humans on Earth act more
responsibly to ensure survival before we colonize, or we need to know how to
insure that those people who colonize are not so prone to make the same
mistakes their Earthly brothers do. If space colonization ends up
amounting to running away from our problems, we will not have changed the odds
of human survival by much. Space colonies would need to be planned in a
way to avoid this fate.