[extropy-chat] Global warming news

Hal Finney hal at finney.org
Sat Mar 25 02:25:45 UTC 2006

Martin Striz writes:
> This is highly speculative.  We can't accurately predict what the
> wearther will be in two weeks, let alone climatic changes over 100
> years.  But even a few meters would be catastrophic to some coastal
> areas.  Some entire island nations, like the Maldives, would cease to
> exist.

Yes, it's speculative.  But it is not a prediction based on weather
models, rather an observation of sea levels last time greenhouse gases
were this high (or actually, not even this high).

> Even without glacier melting, the thermal expansion of the top strata
> of the ocean is estimated to be about 50 cm per centigrade rise in
> ocean temperature.

That's a little higher than estimates I have seen.  For example
http://www.cru.uea.ac.uk/cru/info/slr/ estimates that the last 0.5
degrees C rise in ocean temperature has raised sea level 2 - 7 cm due to
thermal expansion alone.  That would correspond to 4 - 14 cm per degree C.
But I gather that this is an area of some controversy.

> How long will it take to process a volume of air that is 2 billion
> cubic miles (200 million square mile surface x 10 mile elevation)?

Air is well mixed over the relevant time frames, from what I understand.
But your point is well taken.  The question is, how much carbon needs
to be removed from the air?  Running some numbers it looks like a
daunting task.

This Peak Oil web site had a good summary of the carbon budget by Stuart
Staniford, one of their best commentators:
http://www.theoildrum.com/story/2006/1/26/0299/33391 .
This shows that we are presently adding a net of about 4 gigatons of
carbon per year, from this graph:
http://www.theoildrum.com/uploads/12/net_carbon.jpg .

What I imagine with nanotech or biotech is some easily replicated,
inexpensive technology to remove or fix carbon from the air.  To get an
idea of the scale, I look at what would be needed per person.  It's not
literally that every person on earth would have such a device, but this
gives an idea of the scale.  4 gigatons per year with a population
of 6 billion is 2/3 of a ton per person per year.  Sequestering that
amount would just match the amount being added to the atmosphere, so we
would need to do several times that in order to start cleaning the air
of carbon.

That amounts to several tons per person per year, or perhaps 10 pounds
per person per day.  That's clearly a substantial amount.  It doesn't
have to turn into diamond, just some kind of stable, storable form
of carbon.  We would need to put it somewhere that it wouldn't get into
the atmosphere.

I've also tried taking a cut at figuring the energy budget.  It's been
a long time since I studied chemistry but we'll see.  Let's suppose we
are going to go ahead and create solid diamond; I imagine that would
be the most stable and energetically favorable end product.  I found
a reference that combusting 1 mole of solid diamond with 1 mole of O2
produces 1 mole of CO2 + 393.5 kiloJoules.  So it will take that much
energy to run this reaction in reverse and produce 1 mole of diamond.

10 pounds of carbon per day is about 5 kilograms, and at 12 grams per
mole that is 400 moles.  Times 393.5 kJ that is approximately 160 MJ!
Spreading it out over 8 hours (assume it is solar powered) that will
require about 5 kiloWatts per person of solar power to sequester the CO2.
Pretty substantial.  You'd have to wonder if the excess heat dissipation
from creating and storing all this diamond wouldn't defeat the purpose
of removing the CO2 from the air.

This is clearly not a technology that is just around the corner, to say
the least.  It may not be completely impossible given what we imagine
will be feasible in a few decades.  Nevertheless it's not necessarily
the best use of our energy budget and other constrained resources.

I should note that there are other proposals that would also
become practical in this time frame, such as injecting aerosols into the
upper atmosphere to increase the albedo and cool the planet directly.
This happens naturally to some extent and with future technology we
should be able to mimic and extend the natural process.  Then there
are the various space-based concepts to block sunlight as well.

The bottom line is that unless we are willing to just give up and let sea
levels rise, we will need to take charge of the planet's energy budget.
Hopefully we will have the tools necessary to achieve this well before
things get too far out of hand.


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