http://www.smh.com.au/environment/the-bizarre-ideas-that-could-help-the-world-20090312-8wig.html

Enhanced weathering is a geochemical scheme which is highly controllable. The costs are such that somewhat less than 1% of the gross world product, about equal to the sum of world military budgets, would suffice to slightly more than remove all of the current (2007 CE) excess carbon dioxide added by humans.

Well, maybe slightly more. Still working out all the costs.

Did you get answers to your questions at Rabett Run? I looked at investing 50 kJ/(mol CO2) to do two things: comminute olivine to 25 microns (40 kJ) and lift the powder 5 km above the grinding site (10 kJ), so that as they settle at 0.06 m/s the wind can carry them far.

If their magnesium becomes magnesium bicarbonate dissolved in the sea, they take down twice the CO2 my calculations were based on.

I see no reason why CO2 wouldn’t eat them right to the centre of a grain. At http://www.geology.yale.edu/~ajs/1999/07-09.1999.07Velbel.pdf the weathering rate is given. Ferrous iron, as it gets oxidized to ferric, helps break up a grain, even though I don’t think it binds any CO2.

— G.R.L. Cowan (How fire can be domesticated)

But back to geoengineering, the Earth and ocean based version – I expect it will be needed, mostly because of the heels dug in unwillingness of humanity to face AGW head on, even that proportion of humanity that takes the issue seriously. By the time it is treated with the urgent seriousness it deserves, atmospheric levels of GHG’s will be much more than present and be a serious danger; the need to get them out of the atmosphere when major sinks are saturated or turning into sources as warming causes their existing load to be released.

Some geoengineering wants to reduce CO2, a Good Thing.
Others want to increase albedo, to reduce heat, at least in part to lessen the bad positive feedbacks.

For the latter, I’d observe that synthetic volcanoes or mirrors in orbit reduce sunlight over large amounts of the world, *including g*:

- agricultural land
- solar PV and solar thermal

I don’t mind the ships that do clouds in the ocean, but I’d sure rather let sunlight come at 100% in many places, and *use* more of it [for electricity or heating water or growing things], or at worst, cover unusable land with mirrors. The post has some numbers about albedo requirements.

Put another way, I think the {sulfates, satellite} albedo-increase path is dominated by potential terrestrial solutions. They don’t reduce the CO2, but maybe they could hold off tundra melt.

Well, maybe slightly more. Still working out all the costs.

— G.R.L. Cowan (How fire can be domesticated)

He suggests getting fossil CO2 emissions down to close to zero in 2050 and being carbon negative thereafter – a commitment to action that spans centuries – to return global temperatures to beneath 1 degree Celsius warming “is plausible technically” and “goes beyond the technically and economically feasible pathways published elsewhere”.

http://www.guardian.co.uk/environment/2009/jan/16/white-paint-carbon-emissions-climate

Perhaps we would create more emissions producing the vast quantities of white pain needed.

“Work for the dole”- painting rocks white – could be useful after all – the answer to our unemployment and recession woes:)

Mirrors in space are obviously SACTCAR, like sulphate aerosols. Interesting fact: one BTRO method has been demonstrated on a considerable scale inadvertently. This is probably 99.9 percent of the CCS that has actually happened.

Doing it on a gigatonne scale, on purpose, is one of the geochemical schemes that Boyd apparently considers to be hard to stop on short notice. What if it someday turns out that the project of easing the atmospheric CO2 concentration back to the preindustrial level must be brought to an emergency stop? What if, in 2025, having with much effort got the atmospheric CO2 concentration back down to 370 ppm despite China’s having put up 150 gigatonnes of CO2 in the 20-teens, we then find that the CO2 level must be allowed to start rapidly rising again, like now?

Seems like a very remote possibility, and anyway, what is the difficulty with turning off a lot of rock crushers and blowers?

— G.R.L. Cowan (How fire can be domesticated)