Green the Sahara

[David B. Benson]

Irrigated afforestation of the Sahara and Australian Outback to end
global warming
http://www.springerlink.com/content/55436u2122u77525/
(The pdf is available to all).

This geo-engineering proposal considers some of the side-effects.

[James Annan]

I find the response to this sort of paper to usually be an interesting
litmus test for the degree to which people have projected their own
politico-socio-economic wishes onto the canvas of climate change.

There are those for who this will obviously negate the need to think
further about fossil fuel consumption, as it basically solves the
problem (if there ever was a problem). There are others who will argue
that this is no good, it is bound to have other effects, and what we
really need to do is reduce consumption of fossil fuels (and probably
everything else).

Probably the truth really is somewhere in between (by which choice of
words I am trying to avoid the trap of indicating that the truth is
likely to be half way between the worst extremes on both sides, ina
"false balance" stylee).

James

[David B. Benson]

On Sep 8, 7:45 pm, James Annan <james.an...@gmail.com> wrote:
> ...

> There are those for who this will obviously negate the need to think
> further about fossil fuel consumption, as it basically solves the

> problem ...
Unfortunately, it would be very expensive. Who pays?

> ... it is bound to have other effects, ...
Certainly would. Some would be steady employment in a
part of the world which needs sources of employment;
a steaedily growing supply of biomass derived energy
sources to directly compete with coal and natural gas;
the possibility of enhancing or reducing North Atalntic
tropical cyclones; reducing the Mautitanian coast
fishery.

> ... half way between ...
Yes, mst unlikely.

[Michael Tobis]

I have several doubts.

Chief among them is this: it is important to understand that even if a
biofuel plan is sustainable, it is not necessarily a sustainable
carbon sink. In general, deforestation is a one-time source and
afforestation a one-time-sink. Is there something different here?

Secondly, if we expend the capital to irrigate, say, Australia, is
biofuel the best use of that massive endeavor? Fuels, for all their
importance are cheap. Indeed, they are mostly important because they
are cheap.

Thirdly, I'm not sure that the coupling between land surface and
rainfall is one of the more robust model results, so I don't think we
ought to bet the farm on it.

I'm all for instrumental solutions if they actually work.

mt

[David B. Benson]

On Sep 9, 12:26 pm, Michael Tobis <mto...@gmail.com> wrote:
> I have several doubts.
I do as well, but mostly about the optimistic
asssumptions for water requirements.

>
> Chief among them is this: it is important to understand that even if a
> biofuel plan is sustainable, it is not necessarily a sustainable
> carbon sink.

When steady state is reached, begin burying compressed biochar
(essentially high grade coal) deep underground (like coal).

> ...

> Secondly, if we expend the capital to irrigate, say, Australia, is
> biofuel the best use of that massive endeavor?

No. Both the Outback and the Sahara have plenty of sun. As both
reverse osmosis and pumping have interruptable power requirements,
solar thermal will do. Sell the biofuels to compete against fossil
fuels.

>Fuels, for all their
> importance are cheap.

Petroleum based fuels won't be in decades to come.

> Indeed, they are mostly important because they
> are cheap.

I disagree. People need transportation, electricity and heat at
current and projected population densities.

>
> Thirdly, I'm not sure that the coupling between land surface and
> rainfall is one of the more robust model results, so I don't think we
> ought to bet the farm on it.

I'm not sure I understand, but the authors are far too
optimistic about the ability to carefully control water so
that none is wasted. For the Sahara, gum trees are
probably the wrong choice; I suggest beginning with acacia
and sand willow. The Chinese find sand willow around the
Gobi works well to help control desertification.
By starting one would discover the amount of water required. That
requirement, even if larger than the authors state, does not make the
plan impossible; the difficulties are raising the capital and also
political.

>
> I'm all for instrumental solutions if they actually work.

I am as well. I actually think that, near sea coasts,
making biomethane from algae in tanks can compete against
natural gas. The further inland one goes the higher the
transportation costs, not so much for water or gas, but
for removing biochar, for example. Biochar uneconomic to
transport could be sequestered underground.
So it may well be that the enitre project cannot pay its
own way. It would lower the use of fossil carbon, those
requirements being met by biological carbon. It would continue to
store large amounts of carbon above ground every year for about a
century. Thereafter one sequesters more compressed biochar deep
underground.

[James Annan]

David B. Benson wrote:
> On Sep 9, 12:26 pm, Michael Tobis <mto...@gmail.com> wrote:
>> I have several doubts.
> I do as well, but mostly about the optimistic
> asssumptions for water requirements.
>> Chief among them is this: it is important to understand that even if a
>> biofuel plan is sustainable, it is not necessarily a sustainable
>> carbon sink.
> When steady state is reached, begin burying compressed biochar
> (essentially high grade coal) deep underground (like coal).

Or use it as biofuel. But 100 years of carbon sink would be a pretty
good solution regardless of its finite nature.

>> Thirdly, I'm not sure that the coupling between land surface and
>> rainfall is one of the more robust model results, so I don't think we
>> ought to bet the farm on it.

It is widely accepted in the paleo community that the biofeedback is an
important factor in the greening of the sahara 6000 years ago.

James

[ned haughton]

And people always forget the desert biodiversity...

ned

[hgerh...@yahoo.co.uk]

> Probably the truth really is somewhere in between

I think this isn't just about hard science where there is indeed one
(though maybe difficult to discern) truth.

People can have very different opinions about what sort of world they
find desirable to live in. There is no one truth in between the
extremes of thinking that world population should be 10 million with
most of the world left untouched and those 10 million living close to
nature and thinking that actually you wish for humanity to conquer
space and in the mean time you want as much of nature appropriated for
human use as feasible.

[Michael Tobis]

Oddly I sympathize with both of Heiko's extremes, but in either case
it is very long term thinking.

I think most of us can agree that we DON'T want an abrupt and
involuntary population collapse in the current century or the next. It
seems that goal is quite enough to keep us occupied for the present.

mt

[David B. Benson]

On Sep 9, 8:25 pm, ned haughton <naught...@gmail.com> wrote:
> And people always forget the desert biodiversity...

Haven't forgotten. But much of the Sahara was an open wooland
savannah about 6000 years ago, this this plan just speeds up the
cycling. Nor would all of the Sahara be so modified, for variious
reasons.

[Michael Tobis]

On Wed, Sep 9, 2009 at 8:11 PM, James Annan <james...@gmail.com> wrote:

> Or use it as biofuel. But 100 years of carbon sink would be a pretty
> good solution regardless of its finite nature.

How can it be so large? If the present perturbation is less than 20%
due to deforestation, and we need something like triple the present
perturbation to balance the coming century, even if the great deserts
can compensate for all deforestation to date it seems off by an order
of magnitude.

Admittedly I haven't RTFP...

mt

[David B. Benson]

On Sep 10, 2:24 pm, Michael Tobis <mto...@gmail.com> wrote:
> ...

> How can it be so large?

The idea is to counter all sources of pertubation to the carbon
cycle. The proposals in the paper just counter the addition of fossil
carbon.

[Michael Tobis]

David, you miss my point. I am comparing the effect of the proposed
afforestation to the effect of the observed deforestation. To match
expected CO2 for the next century appears to be a mismatch in
magnitude. I estimate that afforestation will do about as much good
for the carbon balance as deforestation did damage. This appears to be
about 15 times too small, which is a big enough gap that it causes me
concern.

What accounts for the difference?

mt

[David B. Benson]

On Sep 10, 3:08 pm, Michael Tobis <mto...@gmail.com> wrote:
> ...

> What accounts for the difference?

Sahara Desert is almost the same size as the lower 48; Australian
Outback about 60% of that. Modern deforestation pales into near
insignificance in comparison.

[hgerh...@yahoo.co.uk]

Few would disagree with that. Maybe I chose a bad example. Let me
choose another one. You can also be for or against greening the Sahara
mainly on the basis of the geopolitical impact. You could for example
be against / for the scheme, because you think it'll do something
about terrorism. My point was that not everything is a strictly
scientific question where there is one right answer only. A question
like whether the Sahara should be greened by big water schemes differs
fundamentally from say "what is the speed of light?". For the latter,
you don't take ten class room answers and choose something in the
middle, one person can have it right and nine wrong (and if the one is
an astronomer and the nine are car mechanics ...). For the former,
democratic, political value choices do matter, and it is rather
annoying when some scientist comes along and says "I am the expert and
if I say this is a good/bad idea, it is so, and non experts should
trust me, because this is a scientific question with only one right
answer with no need for them to provide input for coming to a decision
as to what needs to be done".

[Tom Adams]

There is a social movement that thinks that global warming does not
matter, because technological advances will swamp the whole issue
soon:

http://en.wikipedia.org/wiki/Singularitarianism

A tiny movement at this point, perhaps.