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Noah Deich, the executive director for the Center for Carbon Removal, ruminated on the directions planetary-scale carbon removal schemes might take. The list of proposals is extensive and growing, he notes, but they generally fall within two "capture pathways:" biological and chemical.
Biological carbon schemes largely rely on natural plant photosynthesis to snare carbon from the air. Though Deich observes this is an essentially "carbon-neutral" phenomenon—plants use carbon from the air to build vascular tissue, but the carbon is released back into the atmosphere when the plants die and decompose—the process nevertheless can be tweaked to lock up large amounts of carbon for long periods of time. For example, you can literally farm for carbon.
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Restoring ecosystems—particularly wetlands—is a promising avenue for carbon removal."Many ecosystems provide natural carbon sinks, but they (may have been) degraded over time by agricultural and urban expansion," Deich explains. "Restoring carbon-storing ecosystems like peatlands and mangroves can aid in mitigating climate change, while also providing numerous other ecosystem services (such as clean water, open space, wildlife habitat and fisheries enhancement)."
Another encouraging option is reforestation. The extant prime example is Reducing Emissions from Deforestation and Forest Degradation (REDD), a 2005 initiative by the United Nations Framework Convention on Climate Change. While its results have been mixed, the thinking is that since deforestation may account for 10 to 30 percent of atmospheric carbon emissions, planting lots and lots (and lots) of trees may reverse or at least stabilize accumulating greenhouse gases.
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Chemical carbon storage offers somewhat more limited options, involving two basic approaches."Direct air capture and storage includes technologies that can capture industrial-scale quantities of CO2 from ambient air using solvents, filters or other methods," Deich notes. But there's an inherent drawback: "Direct air capture systems are energy consuming—not energy generating—so they generate net-negative emissions only when the sequestered CO2 is greater than the CO2 emitted to power the system."
Mineral capture and storage, on the other hand, is a passive process that exploits the natural CO2 sequestering qualities of some minerals, such as silicates. By extracting, crushing and spreading such minerals over large areas, Deich maintains that significant quantities of CO2 could be captured and stored.
Carbon remediation schemes that are cost centers will probably fail, but schemes that are profit centers might succeed. Can money be made by mining carbon from the atmosphere?
(Score: 0) by Anonymous Coward on Tuesday December 15 2015, @01:31PM
Do you happen to know the amounts it could do? How many watts of power did it need to be worthwhile? Did it destroy the anodes? If so on what timeframe?
(Score: 4, Interesting) by Covalent on Tuesday December 15 2015, @05:26PM
You are very perceptive: The biggest problem was actually anode destruction. Graphite was the anode of choice in my research, and it worked well enough, but was expensive and fragile, both very bad things. Lately there has been some work in that department, but I think it's still not quite ready for prime time.
The math is obviously a bit more complicated than what I'll list here, but the tl;dr version is:
The array is too big to single-handedly solve climate change, but smaller versions could go be a piece of the puzzle.
The long version -
Assumptions:
1000 W/m2 at the equator
Average of 10% conversion at 3.5V (this has improved somewhat since I did my thesis, but I wanted to be realistic)
8 hours daily average insolation
10 Gigatons of CO2 removed per year for 100 years.
Before I continue, this number was fraught with uncertainty. We are currently emitting about 9 GT / year NET (it was less when I did my research). But I wanted to return us to 350ppm, which requires removal of all emissions of the excess CO2 in the air. Anticipating future emissions was rough, and anticipating Earth's ability to store those emissions was tougher, especially considering that about 25% of global CO2 emissions are stored in the oceans already. But this number works for simple math - you may adjust at your leisure.
Calculations:
1000 W/m2 * .10 /3.5 = roughly 30A of DC current/m2 of panels at 3.5V (the necessary voltage for high efficiency electrolysis)
10 Gt * 1E15 g / GT * 1 mol / 44g CO2 * 2 mol e- / 1 mol CO2 * 96500C / 1 mol e- * 1 s * m2 / 30C * 1 min/60s * 1 hr/60min * 1 day / 8 hrs * 1 yr / 365 days
1.39 E 11 m^2 of solar panels
This is about 140,000 km2 or a square about 372 km on a side. (roughly equivalent to covering Tunisia in solar panels).
Now, this is an enormous array, to be sure. Far too large to construct in decade, much less a year. So this isn't THE solution.
But it wouldn't need to be installed all at once, and it could be put partially or completely over the ocean. There was about 30GW of solar installed in 2014 alone, which is about .3 billion m2. Suppose we double our current output of solar panels (not a crazy idea, as the production is growing exponentially) and installed the additional 30GW of production into equatorial deserts an coastal waters. By the end of the century, we would be absorbing more than 2% of our current CO2 output, and providing enough free chlorine to provide PVC plumbing for the entire developing world and also to chlorinate all of their water. In addition, this is not taking into account significant improvements in solar efficiency (which have and continue to happen) and also reductions in global emissions (which have been less forthcoming but show signs of appearing).
Long story short, you need several metric shit tons of solar panels to make a dent in climate change, but we make a metric shit ton every year. But you'd be better served just replacing coal plants with these solar panels, rather than carpeting the desert with them.
You can't rationally argue somebody out of a position they didn't rationally get into.