Since we're past the point where emissions cuts alone can keep long term warming below 2 C, I do expect active geoengineering efforts later this century. Solar radiation management with aerosols is not a long term fix but could keep positive feedback effects damped while slower long term fixes (like emissions reduction plus accelerated silicate weathering) roll out.
The attractive thing about sulfate aerosols is that they could be formed from sulfur dioxide, which is cheap to form via sulfur combustion and disperses excellently because it's a gas. Delayed oxidation reactions cause SO2 to form nuclei for aerosols. Even though calcium carbonate is also inexpensive, I don't think there is a comparably cheap/easy way to deliver a fluid precursor for it to the upper atmosphere. The closest I can think of is aerosolizing a calcium hydroxide solution that would carbonate in situ via reaction with atmospheric CO2... but calcium hydroxide is only slightly soluble in water. You'd need to lift a lot of extra water mass.
Sort of. One could release sulfur dioxide (or burn sulfur to form sulfur dioxide) at high altitude, or release slower-reacting sulfur species like carbonyl sulfide from surface locations. In any of these cases what will happen is that reactions with nitrogen oxides, ozone, light, atmospheric moisture, and other particles will ultimately convert the sulfur to sulfuric acid, which will then form additional particles of high reflectivity.
It would somewhat increase the surface precipitation acid burden, similar to the acid rain that was a byproduct of 20th century industrialization, but most sulfur oxides that come from power plants or metal refining are flushed out of the lower atmosphere by precipitation. By directly or indirectly adding SO2 to the stratosphere instead of the troposphere, the ratio of reflection:acid content would be higher than that of incidentally produced waste-product SO2. (That's why we can't start cooling the planet just by removing sulfur controls from existing coal plants; most of that SO2 would produce acid rain accompanied by little additional sunlight reflection.)
Relatively minor, nobody's talking about blocking 50% of the sunlight, more like 1-2%.
Pretty straightforward for direct photovoltaic generation, but the wider consequences on the (very complicated) Earth system are hard to say. Would it affect wind patterns (and wind power generation as a result)? What about plants/animals/agriculture?
I mean, you have to ask yourself what you actually believe about the climate.
Do you think that climate change is somewhere between "unbounded costs ranging in the hundreds of trillions of dollars over the course of 2050-2150," and "the death of humanity and/or all multicellular life on Earth"?
Because if so, the side effects of geoengineering probably aren't that bad, and even if they are, they're apparently only as bad as what you think the costs of doing nothing are.
On the other hand, do you think that climate change is either non-existent or some kind of relatively mild thing that will cause $100 Trillion dollars or less over the course of a century? Then probably geoengineering is not for you -- but that also means that you're somewhere outside the orthodoxy on climate change.
If you believe that climate change is a real big problem (ie, hundreds of trillions of dollars or much more in damages over a century timeline) AND that it is stoppable by being really persistent in asking people to use solar and wind power, then I don't think that you're being very realistic.
I don't think that you understood my comment very well.
So, look, if you don't believe that climate change will be disastrous, then you're perfectly within reason to say that geoengineering is a really bad idea. The beef that people have with you will not be that you're wrong to be opposed to geoengineering, their beef will be that you're wrong to think that climate change is no big deal. I'm not here to fight that fight. If that's your position, fine.
If you DO think that climate change is a big deal (and by big deal, I mean you think it's somewhere between "likely to stall all economic growth worldwide for centuries" and "likely to kill all of humanity"), then it's kind of hard to imagine what worse consequences geoengineering could possibly have.
And particularly, if you do think that climate change is a big deal (as described above), there aren't a lot of very realistic options besides geoengineering. It may be that even if we stopped ALL carbon emissions RIGHT NOW, we'd still have really bad climate change. And obviously, realistically, we just won't stop all carbon emissions now. We won't stop all carbon emissions in a decade, or two decades, or three. I am prepared to argue with you if you imagine that we can stop all carbon emissions now.
The only fourth way I can imagine is that someone might somewhat reasonably believe that in the near future, technological advance will get us out of this. That we'll discover some way to do massive carbon-less power generation at very low cost and/or that we'll discover an obviously unproblematic way to do carbon sequestration on enormous scale. I will say that if you assign a high probability of disastrous climate change, I don't see how you'd assign a similarly high probability of those exact technological advances. In fact, I might call such precise foresight... hubris.
I'll give you this... your ending was well played.
And I'll grant that if you truly believe that climate change is "likely to kill all of humanity", that easily leads to a "damn the consequences" attitude toward fighting it.
However, your expression of the alternatives eliminates a lot of nuance. For example, suppose that climate change is "likely to stall all economic growth worldwide for centuries", meeting your definition of "a big deal". Is it really hard to imagine what worse consequences geoengineering could possibly have? What if geoengineering is "likely to kill all of humanity"?
So, yes, I'll remain at least as concerned about geoengineering (and "damn the consequences" thinking) as I am about climate change.
1. I think that you're probably underselling "stall all economic growth for centuries." It's not that different from "kill all humans" (for example: it would be hugely globally destabilizing. The odds of nuclear war would go way, way, way up. For another example: it might well either restart exponential population growth like we had in the late 19th/early 20th centuries, or else cause a demographic death spiral).
2. It's pretty hard to believe that climate change is very likely to go right up to the edge of "stall economic growth" and not have a very significant chance of tipping over to worse scenarios. You already implicitly believe in some positive feedback cycles here.
3. It is actually pretty hard to imagine that specifically aerosolizing sulfur dioxide is going to cause really catastrophic consequences that global warming won't already. As other commenters have pointed out, volcanic eruptions cause massive sulfur releases already. If you believe that the environment is so, so, so sensitive to any changes that any change you might make is likely to cause spiraling destruction of the ecosystem, well, then doesn't it seem likely that our many existing changes have already sent us past the point of no return? Like, if we're making 100 changes on the scale of sulfur release (which we are), and one change much, much, much larger than sulfur release (carbon release), it seems a little unlikely that sulfur release is the straw that breaks the camel's back.
There are some possibilities for nuance here! You can reasonably believe that, for example, ocean acidification is the bigger problem than temperature change per se, and sulfur release doesn't solve ocean acidification, and indeed may slightly (very, very, very slightly) contribute to it and more importantly may encourage people to regard carbon release as unproblematic and thus encourage more carbon use and thus more ocean acidification.
But I don't usually see people making targeted critiques like the one above, the kind of critique that only applies to one specific proposal. It's usually just sort of a general reaction to anything other than reduction targets. And, honestly, reduction targets aren't going to work, guys. Not alone.
The half-life of sulfur aerosols in the stratosphere is on the order of a few months. So if there turns out to be some overwhelmingly undesirable side effect, we can just stop putting the sulfur up there and the effects will dissipate relatively quickly.
Nature does this experiment for us every so often: large volcanic eruptions, such as the 1991 Mount Pinatubo eruption, put massive amounts of sulfur into the stratosphere, much larger than the amount we'd need to use. So it's pretty likely we would have noticed the negative effects if there were any (beyond the fact that we got much more cooling than we wanted for a couple of years).
On the other hand, anthropogenic climate change is already going to screw all those things up, so it's not like avoiding geoengineering is necessarily the right choice either. Just need to understand the potential risks and benefits as well as possible before considering it.
As someone who grew up hearing stories about the unintended environmental damage caused by many well-intended Corps of Engineers projects, geoengineering makes me cringe.
Edit: I probably should have found a way to use "hubris" in that sentence...
It's a reasonable concern, but whether to modify the biosphere is not a choice we have any longer. We are modifying it -- that's what all that CO2 that we are already putting into the atmosphere amounts to. Geoengineering is about looking for ways that we can modify it intentionally along with the unintentional modifications we are already making.
Caution is certainly warranted, and there is some danger of hubris, but running screaming from the room is not a productive response either.
Yeah, but I'm not running screaming. Just asking that anyone submitting a proposal for geoengineering please include plans of equal or better feasibility and speed for an undo button, should the need arise.
another naive article, this time from Harvard, that fails to mention the term "ocean acidification". At some point krill cannot form their exoskeletons, bringing an abrupt end to whales and other sea creatures.
I don't think it's reasonable to expect every article about global warming to mention "ocean acidification". Displacing fossil fuel power generation with nuclear power plants would certainly reduce ocean acidification, but nevertheless most of the nuclear power articles I've read neglect to mention this fact.
There are other forms of climate engineering that would address C02 directly. One that's received a fair amount of press is "iron fertilization"[1]. I don't know, but my guess is that most people who talk about "solar geoengineering" (of any sort) probably think we're going to be doing solar geoengineering, iron fertilization, and probably multiple other forms of climate engineering at the same time. But not every article that discusses iron fertilization mentions sulfur dioxide, and not every article that talks about stratospheric sulfur dioxide mentions iron fertilization.
The attractive thing about sulfate aerosols is that they could be formed from sulfur dioxide, which is cheap to form via sulfur combustion and disperses excellently because it's a gas. Delayed oxidation reactions cause SO2 to form nuclei for aerosols. Even though calcium carbonate is also inexpensive, I don't think there is a comparably cheap/easy way to deliver a fluid precursor for it to the upper atmosphere. The closest I can think of is aerosolizing a calcium hydroxide solution that would carbonate in situ via reaction with atmospheric CO2... but calcium hydroxide is only slightly soluble in water. You'd need to lift a lot of extra water mass.