It is just curiosity that forced me to ask this question. At some point in time, if we can't control global $\sf{CO_2}$ emissions, temperature will increase until a tipping point and it will be a complete catastrophe. However, if we could prepare ourselves through geo-engineering (e.g. carbon removal, blocking solar radiation), then we may return the temperature back to normal. I am not saying that we have to experiment with mother Earth, but if we may do weather-engineering experiments in controlled labs just like the Large Hadron Collider(LHC), we may some day be able to save the planet from catastrophe.

So, my question is, how bad does geo-engineering go as far as controlled experiments done in totally isolated labs?

In NWP models, it is mostly possible to control the evolution of $\sf{CO_2}$, solar radiation, moisture, temperature etc. Given the current computation power is better than in the past and will most likely be better in the future, once we have calibrated and validated those climate/weather models, can we use them to fight extremes of weather like floods, drought, hurricanes and all other wind storms?

The accuracy of current weather predictions is better for forecasts 5-10 days ahead. So, this may give enough time to do controlled simulations before and after our intervention. Based on that we may act on to, for example, increase precipitation (e.g. through controlled spraying of condensation nuclei) where there is drought, hit and disperse hurricanes or change their directions before they hit and damage cities etc. How wrong can one be to think like that?

• Why do you say that geoengineering is 'bad'? In point of fact, what's happening now WRT CO2 is (unintended) geoengineering. Most of the proposed geoengineerings (at least the technically feasible ones) I've seen are 'bad' only in the sense that they are at best band-aid fixes, which attempt to treat the symptoms instead of addressing the root cause. – jamesqf Feb 26 '16 at 6:26
• @jamesqf: that sounds like a bad idea to me. It's like taking pain killers to make it easier to walk on a broken leg. Sure, you can't feel it as much, but you're letting yourself do more damage than you would if you just stopped walking for a while, and you will probably have to live with that damage for ever. – naught101 Mar 3 '16 at 2:24
• @naught101 Strange analogy, but if you get shot, the doctor often doesn't work to treat the root cause, but to stem the troubling symptoms. Bandaids and gauze pads and sutures aren't a bad thing then! Likewise during a heart attack, the most vital thing is the doctor gets your heart beating. Then (and prior) he tries to get fixed what's causing the troubles. Point is, while the fixes aren't usually the most positive option... geoengineering seems about like bandaids and heart paddles in terms of keeping things going when the problem cannot (or will not) be fixed. – JeopardyTempest May 28 '17 at 11:12
• weather is not climate, and its not a good idea to confuse the two. Accuracy of weather models has little to do with accuracy of climate models. – John May 28 '17 at 19:05
• @John. Climate is an average of weather. Weather models are an initial value problems but climate models are a boundary value problems. But the physics is the same. So, at the base they both are the same. There is no confusion here. Geo-engineering could be applied to solve both a weather and climate problems. – Gemechu Fanta Garuma May 28 '17 at 20:42

The bad part about geo-engineering are the unknown unknowns, to paraphrase a certain US politician.

Our climate models are wrong. All models are wrong, but some are useful.. Our models are useful, but not quite useful enough to trust them when they tell us massively spraying stuff into the stratosphere or the oceans is mostly harmless. Our models can't properly reproduce our current climate. They agree about some trends, but there's lots of stuff that they're missing.

We used to use lots of toxic chemicals in our fridges. That was a bad idea, so we found some stuff that wasn't toxic. Great, no? Decades later, scientists realised this was destroying ozone above Antarctica. At first the measurements were rejected because they didn't make sense. Contrasted with our understanding of the atmosphere, and why would ozone suddenly disappear anyway?

Our climate system is complex. Very complex. Mess with one of the symptoms, and who knows what side effects are going to be? It's a risk that we cannot quantify, and those are probably the scariest risks out there. If even with stuff that doesn't seem remotely connected to each other (fridge coolants and ozone) we almost messed up very seriously, who is to say actively messing with our atmosphere or ocean isn't going to have nasty unintended consequences?

Better than offsetting one set of geoengineering (deforestation, ocean acidification, enhanced GHG emissions) with another equally radical one, it might be safer — from a risk management point of view — to try to not do any geoengineering at all. Certainly as long as our understanding of climate is just starting.

To borrow an analogy from medicine: preventing is better than curing. Patients are sometimes prescribed medicine where the side-effects are so bad that they're almost lethal by themselves, but only when the patient is surely terminally ill, so there is "nothing to lose". We do have a lot to lose on Earth.

Note that weather models are initial value problems and climate models solve boundary value problems, so mathematically speaking, the two are completely different.

Seconding eveything that @gerrit mentioned.

Additionally, another major problem with geo-engineering is that once we've started these processes and essentially borrowed time to offset mitigation measures, we'll have put ourselves in a situation where these measures will need to be continued almost indefinitely, regardless of the risks of negative side effects of geo-engineering to begin with (ie: chemical intrusions, biological system degradation, geopolitical concerns). Present climate models suggest that if we were to engage in climate engineering and then remove these after several years, warming rates will come back with force (http://iopscience.iop.org/article/10.1088/1748-9326/4/4/045103).

• This is particularly the case with artificial aerosol cooling, because you're masking warming, and as soon as the aerosols are removed from the atmosphere, the warming starts again (and with more CO2, so stronger). It's also a problem with Carbon Capture and Storage, which always has some minor leakage - you're effectively putting off the warming from now, and saving it for later. It's still going to happen, either way. – naught101 Mar 3 '16 at 2:23

I've been working, as a hobbyist, on an alternate method of solar sun shading feel I feel I can help answer this question.

Technically, any project which affect the climate of a planet is a form of geoengineering. This includes the current GHG crisis as mentioned by jamessqf above. But reversing GHG emissions to return to preindustrial levels is also a form of geoengineering. Thus, no matter what we do (continue current trends or modify them) we will be performing geoengineering. The lesson from this is that life is a balance.

What most people think of as geoengineering is a large scale project designed to mitigate certain climate effects across a planetary scale. This includes things like releasing aerosolized particles into the air but also things like increasing seafoam or spraying salt/saltwater into the air over oceans to create small clouds that reflect sunlight.

Something else to consider is that often experiments are conducted specifically to fail. Rocket tests that destroy the rocket have been in the news because they wanted to make sure backups work as expected. Science works that way with geoengineering as well. They try to break things to understand how they break better.

Some things else to consider is the effect on different biomes of different sizes. The world literally operates differently for life of different sizes such as a microbe compared to ants, and an ant compared to us. An ant can fall off the empire state building and be just fine and us, well, not so much. Some insects are so small they swim through the air rather than fly. Thus we have to keep all sizes of life in our consideration. Seafoam may cause certain bacteria to flourish and kill others and we might not know for years. This effect might not be that big or it could cause dangerous algae blooms (this is a theoretical example not backed by any experiment). This plays into your LHC example. LHC operates on the smallest units we can manipulate. The earth is the largest unit we can currently manipulate and the rules are very different.

Going back to your original questions and worst-case scenarios we could cause issues with the earth's ozone layer, collapsing it and wiping out humanity, we might cause massive storms, we might kill off keystone species (some of which might exist on a microscopic level making it hard to detect until it's too late) causing great dyings releasing more GHG into the atmosphere.

The most realistic issue is that we don't apply geoengineering evenlyish (I add ish because optimal applications won't actually be even. Studies have shown that adopting certain areas, or engaging only certain areas with geoengineering, will make negative effects of climate change worse in the least modified areas. This means that is the USA implements geoengineering and Africa doesn't Africa will have a harder time. Conversely, studies have also indicated that well-implimented geoengineering can reduce inequality between nations which would drastically boost the quality of life and economy of the world's population as a whole.

Other than that the next most likely possibility is that geoengineering causes some large scale issues which will cause great dyings which will release more GHG into the atmosphere. Life is a giant cycle of carbon and other compounds and messing with that cycle causes levels of different chemicals and elements to change.

I see the argument that once we start geoengineering we can't stop. This is assuming GHG levels are maintained or increased (which is what we are going for) and suddenly removing a technology that lowers the temp by 0.5-2C would result in fast changes than would happen 'naturally'. However, this concern assumes that we only have 1-2 geoengineering projects to work with. A more realistic view is that we will use multiple methods in conjunction. Not only does this redundancy remove the concern that any single project can't be removed but it allows for some projects being better or safer in different circumstances. We will learn a lot, and it lowers the number of unintended side effects for any particular project.

I hope this helps. -Tristan

• We've recently had the following discussion: Do we need to be stricter on enforcing citations? In this particular case you answer seems to stand on its own, but I see you've been very active and have three answers and all are unsourced. It might be a good idea in the future to try to add links to or citation of sources when you are stating facts, not necessarily because most people won't believe you, but it helps future readers read further, it helps avoid disputes and it's generally what people do in Stack Exchange answers. Thanks! – uhoh Feb 5 '20 at 5:40
• "This means that is the USA implements geoengineering and Africa doesn't Africa will have a harder time" - that sounds good for business, we can sell them geoengineering. – user253751 Mar 5 '20 at 15:26
• @User253751 hat would be bad business on their part actually. It's way cheaper to pay people in poor countries to build as much as they can in this field no one is trained for yet. Not to mention the infrastructure needed to keep up with changes. But a well managed boost if geoengineering works will ensure that they have the wealth to then buy everything else and investments might flow in making everyone rich. The problem is that it has to work at least marginally better than it hurts. If two acres become lush for every one that becomes barren then it might have to be the cost we pay for sloth – T.A. McKay Apr 30 '20 at 2:29