Metaphorically speaking, we now have to consider the planetary equivalent of high-risk, high-cost surgery after mostly ignoring the planetary "stop smoking" advice experts have been giving for more than a generation.
Also, any large scale sequestration effort is going to be much harder if emissions continue unabated. We're past the point where prevention alone can stabilize atmospheric CO2 but we're never past the point where further anthropogenic emissions can make the problem even worse.
Naturally occurring silicates of magnesium, calcium, sodium, and potassium are thermodynamically prone to weather to carbonates in ambient conditions, when water absorbs CO2 and passes over rocks. In the case of magnesium and calcium in particular, the weathering leads to stable solids that will not spontaneously release CO2 again. A schematic example with calcium silicate:
CO2 + CaSiO3 -> SiO2 + CaCO3
• The end state is naturally stable. You don't have to worry about the leakiness of underground containment.
• It restores the pH balance of the oceans as well as reducing radiative forcing (warming) effects.
• It deals equally well with point and distributed sources of CO2 (coal plants, automobile tailpipes).
• It can be located anywhere on Earth. It does not need to be adjacent to CO2 sources.
• It does not require concentrated CO2 streams, but works with ambient atmospheric concentrations.
Natural silicate weathering reactions dominate Earth's CO2 balance in the very long term. But they are strongly kinetically hindered in nature. After a freshly exposed rock surface has weathered to a depth of a few microns, the cation-depleted "rind" drastically slows the weathering of the remaining interior. Without human intervention, it'll take about 100,000 years for natural silicate weathering to restore the pre-industrial baseline of atmospheric CO2 concentrations. There are different ways to improve the kinetics:
• Crush bulk rock to a fine sand texture, so full interior weathering finishes much faster (still takes years-to-decades, but no longer takes geological time scales).
• Place crushed rock in near-shore ocean environments where mechanical wave erosion keeps removing rinds.
• Place crushed rock in acidic tropical agricultural soils where it weathers faster due to low pH and elevated temperature. This also improves soil quality for growing crops.
It's not explicitly included in the scholarly literature, but I say that advanced robotics are necessary because the required scale of intervention is staggering, bigger than any engineering endeavor in history.
For example, the Columbia Plateau in the United States contains basalt whose alkali and alkaline earth content could bind about 20% of its own mass in CO2, after complete weathering:
https://crustal.usgs.gov/geochemical_reference_standards/bas...
To neutralize the CO2 that humans emitted in 2015, about 36 billion tons (https://en.wikipedia.org/wiki/List_of_countries_by_carbon_di...), would require mining and pulverizing about 180 billion tons of Columbia Plateau basalt. That's about 60 cubic kilometers. We're in no danger of running out of plateau -- it contains more than 170,000 km^3.
As for energy estimates, the Bond Work Index for crushing basalt such that 80% of particles pass a 100 micron screen is in the neighborhood of 17-20 kWh per ton:
https://www.911metallurgist.com/blog/table-of-bond-work-inde...
I'll add a factor of 2 for overhead to estimate the whole process energy expenditure. That would mean that using Columbia Plateau basalt, you'd expend 40 kWh per ton of basalt, about 200 kWh per ton of CO2 removed from the atmosphere. That is, energetically speaking, really good compared to schemes that try to run "combustion-in-reverse" to regenerate hydrocarbons from CO2. It's efficient enough that you could actually use coal fired power to drive the whole process and it would still be a net CO2 sink. But at 200 kWh per ton-CO2-scrubbed, it would take 7.2 billion megawatt hours to neutralize humanity's 2015 CO2 emissions. That's an annualized power of 821 gigawatts -- nearly twice the average electrical power generated in the United States.
The scale is so vast that I can only imagine advanced robotic manufacturing, mining, and energy generation being up to the task. However you want to modify my baseline scenario -- smaller projects scattered around the Earth instead of one mega-project, being pickier about processing only the best rocks -- I think that the scale is still daunting. But I think it may still be possible because I see automation advancing a lot in the 21st century if we don't precipitate a civilization-ending crisis first.
- Plant heliostat molten salt reactors in desert coastal areas [1]
- Use generated heat to desalinate water
- Use desalinated water to provide irrigation
- Plant (potentially GMO'ed) bootstrapping organisms to create a soil (greening)
- Plant trees
- Rinse repeat.
However, your idea makes more sense if the only goal is CO2 scrubbing. But adding the heliostat molten salt reactors in a desert might be quite feasible, they generate tons of heat, which can be translated into energy or simply mechanical force (water pressure)…and there is no shortage of silicates in the desert.
[1] http://www.solarreserve.com/en/technology/molten-salt-energy...
Accelerated silicate weathering and "greening the deserts" are concepts that work well together, too. Mature fertile soil contains weathered minerals and organic matter. Crushing basalt can speed up the weathering part of producing soil, and provide micronutrients for plants plus a couple of important macros (phosphorus and potassium).
Why not just assume it's going to become unstable in close future and start building with that assumption ? Large scale isolated citiy domes. Nutrient synthesis that doesn't rely on climate/agriculture. Environment independent energy generation like micro nuclear reactors. Large scale air filtration and temperature control.
As the world becomes more interconnected and developed catastrophic outcomes like super virus/bacteria, large scale nuclear event, etc. become bigger threats to entire world. Why not start building self sufficient and well isolated megacities that can function irregardless of climate change ? It's perfectly possible on 50 year timescale if we don't waste time on shoving our heads in to the ground and hoping everything will stay great if we stop burning stuff.
I think the "preserve the environment" is a knee-jerk driven by the same kind of instincts that sell "natural organic food" and stuff - even if we could somehow magically reign in man made climate change there's really no guarantee that the climate will remain stable or that a low probability event like a volcanic eruption won't cause a huge global crisis, etc.
Instead of hoping things remain as they are we should limit our exposure to environment risks.
But to answer your question, because we can't build enough of these to sustain billions of people.
Maybe but then again scaling isn't really the immediate problem - it's building the thing in the first place, replicating should be simpler and by the time it's done who knows what the tech will be.
And while it probably won't work for everyone it will work much more reliably for those that participate in it - not just for climate change but for other catastrophe protection/isolation as well.
What good does convincing people do if the government won't even admit climate change is real?
The "huge" savings for our industry are minimal in the grand scheme of things. It's depressing to realize how we are past the prevention phase of climate change and rapidly passing through chances to more easily mitigate the impacts.
It doesn't have to be for our survivors... We could, and I believe we should, do it for the next civilization to come after ours, even if it's a few alien visitors.
If for no other reason than to leave a legacy of our short existence against the infinity of this universe.
You said it yourself: If you can't mobilize man to fight climate change, you aren't going to mobilize him to prepare for it either.
Basically, if an oil tanker is leaking oil all over the beach, we should first plug the goddamn hole before talking about (expensive) solutions to clean up the contaminated beach. Doing it the other way just doesn't make sense.
If the US government was actually focused on prevention, that would be a huge step up from "denying there's a problem."
AFAIK, anything can go wrong anywhere.
Never attribute to forethought that which is adequately explained by stupidity.
Wonder who might be involved there...
https://www.2b1stconsulting.com/exxonmobil-and-rosneft-set-j...
Last time I checked as a nation we are working hard to reduce emissions have some of the lowest in the world. Perhaps it would be more useful to go and bash China and India, two countries in which seeing a clear sky in a large city is a rarity.
It doesn't feel like its a problem because of two reasons:
1. Pollution and CO2 emissions are two separate issues. The US has strong pollution regulations regarding pollution near large populations, so even if it contributes to the green house gas problem for people living in cities air quality is good.
2. The US was previously the global leader in pollution by a wide margin, producing 300x what Brazil produced for instance in 1950. In recent decades, manufacturing in the US has become cleaner bit by bit, so there has been improvement. This is unfortunately dwarfed by the quality of Europe where pollution was always a lesser problem, and environmental guidelines became more stringent faster than in the US.
Many people like to compare the US to Europe, and in that respect the US usually looks terrible but the US isn't Europe and has never been in the same place socioeconomically. It is better to compare the US to China or India, because in geopolitics we are in the same place---large manufacturing nation, large population, large geography, former colony, quasi-imperial ambitions.
[1] https://en.wikipedia.org/wiki/List_of_countries_by_carbon_di...
https://wri.org/blog/2014/11/6-graphs-explain-world%E2%80%99...
Consider this: People today are still dying from landmines and poisons that were using during wars a 100 years ago [0]. They may remain around for over 300 years [1].
The things that will most immediately affect the civilization after ours will probably be our radioactive waste, the long-term effects of climate change, the extinctions caused by us, unexploded mines and bombs, and stockpiles of nuclear and other weapons.
At best, the next civilization may dig up some of our machines and partially reverse-engineer them, but they'll probably never be able to access their original functionality. For example using our laptops/phones as a source of light, or their batteries as explosives. What little technology of ours that still fully works by then, will probably cause wars over its ownership, even if the tech itself is benign and beneficial.
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If, like me, the idea of accumulation of technology over large expanses of time, across multiple civilizations and potentially multiple species is deeply interesting to you, you may love the world of Numenera [2] [3]; Earth, a billion years from now.
[0] https://news.ycombinator.com/item?id=12187512
Maybe the AIs will pick up where we left off. They'll be sort of human. Especially if hybrids become popular.
Things seem like they are going to get really bad. I try not to think about it too much. It doesn't seem like there's anything I can do.
[1]https://en.wikipedia.org/wiki/Global_dimming
Edit: Changed link to Wikipedia entry
We'll survive as a species, just not as a civilisation.