Stratospheric aerosol injection (SAI) can cool the world in two years: we need a treaty to stop climatechange

Summary

The summer of 2023 has shattered numerous records on climatechange impact and numbers have jumped of the scales.“Climate breakdown has begun”, the United Nations chief has warned as the world went through its hottest Northern Hemisphere summer on record. The image above shows iconicly how numbers have jumped of the the already expected increase: often without clear explanations yet at hand. This makes a clear example how climatechange will likely keep accelerating faster than previously believed, crossing several (irreversible) Tipping points speeding up climatechange even more. At the same time reports tell how humanity is not cutting down emissions fast enough, but rather 12 times slower than needed to reach the goals of the Paris agreements: so in the short term humanity will just not decrease emissions enough.

The head of the UN Convention to Combat Desertification, Ibrahim Thiaw, stated that “Humanity is at a crossroads” when it comes to managing drought, and accelerating means of slowing it down must happen “urgently, using every tool we can”.

This blogs shows SAI can cool the earth in about 2 years back to the 2020 temperatures and keep it there even if CO2 keeps rising, this will stop a large part of the rampage of destruction we have seen in 2023 brought by climatechange warming the earth. This claim follows from the scientific papers and sources in paragraph four and five.

I know how strong people feel against any form of geoengineering, and the internet is full of people telling us not to use any kind of geo-engineering listing all kinds of credible to far-fetched risks. But at the same time the internet is full of scientists warning us “We are afraid, as world enters uncharted Territory”. A distinguished international team of scientists on Tuesday issued the starkest warning yet that human activity is pushing Earth into a climate crisis that could threaten the lives of up to 6 billion people this century

Anno 2023, after reading numerous scientific papers with the latest insights from scientific research, this blog argues it is high time we start to seriously investigate and prepare for stratospheric injection (SAI) as a tool we can and must use.

To drive the point home SAI at this point should not count as unsafe, and SAI is essential for survival, this blog takes 6 paragraphs to describe:

1. The painful conclusion we need to choose an undesired path to save humanity and ecosystems: and a summary of how we can implement SAI safely, considering all real risks
2. A weighing of current climatechange destruction with or without SAI
3. The devastation climatechange is bringing and will bring
4. What SAI is and what it can deliver and how fast
5. The risks of SAI and howto deal with them
6. A rebuttal of real risks of SAI and far fetched or bull shit arguments

Hopefully this blog will point people to the right resources to discuss SAI in depth in stead of the light dismissals currently popular. If anything I do not believe there is a better resource on the topic at this moment (but please do send me relevant resources to take up and I will add them).

Please share this blog widely and copy from it freely!

Written by Hans-Cees Speel. Version 2 (added more sources, rephrased items, increased depth of research)

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1. The painful conclusion we need to choose an undesired path to save humanity and ecosystems: and a summary of how we can implement SAI safely, considering all real risks

I do not desire a world with stratospheric aerosol injection: it is painful to have to conclude, against my feelings, that we however better start it as soon as possible. This pain comes from realizing how bad the impacts of climatechange already are, and then also realizing it will get much worse and if we don’t act our children will face all this powerless. But here we are in 2023 facing reality, if you dare to take it all in.

So my conclusion after reading many scientific papers is we should use SAI nevertheless its risks. How do I get to this conclusion? Well this is the argumentation in short. In the rest of this lengthy blog I will underpin the argumentation point painstakingly with sources.

In summary, the basic reasoning:

1. Climate change has had an enormous impact in 2023 and future impact will likely get much much worse. Impacts are so devastating they can lead to civilization collapse (by means of massive food and water shortages leading to war and chaos). Scientists are literally writing this in papers and politics (weakened by decennia of neoliberalism) largely ignores it. Here a fairly recent paper: We Are Afraid’: Scientists Issue New Warning As World Enters ‘Uncharted Climate Territory
2. Stratospheric aerosol injection (SAI) can take away the most dramatic impacts of climatechange within 2-5 years or so. So we should take this path to avoid collapse and to buy us time to reduce CO2 emissions.
3. However, if SAI would have risks that make it impossible to use, this course of action would be foolish. Therefore I have researched the most important risks and written a plan to manage them. My conclusion is it looks very promising, we are not out of the woods yet, but lets start to find out for sure if its safe enough to cross the street.
4. Given the 3 arguments above we must start building an international coalition to research and decide on implementing SAI (again underpinned at depth below to mitigate governmental and escalations risks.)

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2. A weighing of current climatechange destruction with or without SAI

So what devastation do we get with or without SAI? The mind-map below presents impacts of a world with and without SAI, where climatechange plays out.

If its too small for your screen: here is a pdf

On the right side of the mind-map you can see how most climatechange impacts will diminish or disappear when SAI is deployed. However, we do get a number of risks, which I will address at length below.

As you can see if you compare the left part where SAI is not implemented with the right where it is, SAI does one thing with immense positive impact: it cools the earth and keeps it within a specific temperature boundary. The simple act of cooling down the earth has the following positive impacts:

1. Floods caused by extreme rain events will largely stop
2. Heatwaves on land and in sea will largely stop
3. Forest- fires caused by heat and the resulting dried out soil will diminish
4. Hurricanes and cyclones will be less big and less frequent
5. Weird weather events (like sudden very cold or warm months) will largely stop because the jet-stream won’t wobble as much
6. Arctic ice sheets will stop melting and start growing again. Hopefully not to late to stop slowing of the Amoc
7. Antarctic ice sheets will start growing again, although some melt will continue the first years because of warmer ocean water.
8. Worldwide glaciers will start growing again and water levels in large rivers depending on it will stop going down (unless other causes are lowering water levels like in the Ganges, see monsoon paragraph)

Disclaimer for all of the above: there will of course always be floods and droughts and fires and hurricanes and so on, but the intensity when implementing SAI will be back to the way it was in 2010. And also, how much exactly all this will diminish will probably correlate with the specific design of SAI. If the Irvine half-SG SAI design is chosen impact will be different than a design where more cooling is aimed for (see paragraph on SAI and monsoon).

What about the risks of SAI? However, what about the risks of SAI? In paragraph 5 I will sum up all relevant risks in the categories Governance, Social escalation, and risks to the climate system. Since the main reason to dismiss SAI until now is their fear of its risks paragraph 5 is the longest part of this blog.

But before delving into that tedious tasks I present the summary of how to manage the SAI risks shortly here:

How can we plot a responsible course toward a decision to yes/no deploy SAI? In paragraph 5 I argue we should asap start to built an international coalition to:

1. Research SAI by modelling, testing and gaining knowledge
2. Craft an international treaty to base SAI deployment on, so when it is deployed its goals and implementation will be balanced to protect humanity from run-away climatechange while reducing unwanted impacts, and
3. In this treaty a coalition of India and its neighbouring countries should have a veto, since they bear the largest risks (see risk one on monsoons)
4. Include international monitoring and evaluation of impacts so the deployment can be continuously corrected, and
5. Include controls to help countries or regions that are negatively impacted by monetary means or by accepting refugees, and
6. Include an exit plan, since SAI can only be a temporary control. The real solution to climatechange is reducing CO2 levels in the atmosphere, because SAI cannot solve ocean acidification, which will hit humanity in 20-100 years in an unpredictable but probably relevant way.

So in conclusion, this blog argues: When comparing risks of SAI with a future without it, the risks are manageable. We should dismiss the false argument SAI is too risky: climatechange it too risky not to fix it. This fix must have two parts: decreasing fossil fuel emissions and SAI. We need both. Those who oppose this have not thought about it hard enough.

The rest of this blog I will underpin this central argument with sources and argumentation

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3. The devastation climatechange is bringing and will bring

I completely understand those arguing against SAI: its unnatural and we shouldn’t mess with the earth we depend on. However, we have already messed with the earth so this argument is moot. They go on to argue: but surely we shouldn’t add to this with more meddling? Yes we should. We have meddled and made a mess. We have the responsibility to clean it up as well and there is ample evidence cutting back emissions is not happening timely to avoid disastrous impacts.

Well but how big is the mess we made of the earth by causing climatechange? It is not a pleasant task to sum this up, and people shield themselves from the conclusions and understandably dive away from the pain. Diving away includes making excuses as: you shouldn’t wallow in sorrow and its all a hoax. But we must be responsible and face the dragon.

Below in three parts:

1. A list of disastrous impacts in 2023 and what predictions are made on the basis of this
2. What huge and more silent impacts are not generally in the news
3. The reasons why it will get much worse (tipping points and science being too careful

3.1: A list of disastrous impacts in 2023 and what predictions are made on the basis of this

The summer of 2023 has shown us how climatechange fastly turns into climate disaster. In 2023 climatechange suddenly made a leap for the worst and worsened beyond what scientists could explain. The iconic pictures of the global temperature in September jumping beyond anything seen before and the ice-growth staying behind around the south pole (Antarctica) are presented below.

If you click on the button below you can scroll though a list of sources describing rainfall causing floods world-wide, record forest-fires across the globe, record heatwaves across the globe, worldwide droughts leading to crop failures and water shortages for humans, and heatwaves in the oceans causing animal die-off. In between the disastrous events also predictions how climatechange on its current course will cause water shortages for 5 billion people and food shortages before 2030.

Click here for a list of news sources on 2023 impact of climatechange

3.2: What huge and more silent impacts are not generally in the news

In paragraph 2.1 a long list of impacts that made the headlines is presented, but what less “news-flashy” impact do we have? Below a list of less news worthy impacts. The most concerning are probably slowly depleting water sources that are almost completely depleted now worldwide and ecosystems collapse.

Slowly depleting water resources do not need much explanation probably: humans are causing this because governments are just not managing water sources at all and economic forces without proper government actions have no problem depleting anything. Eco-system collapse for me as a biologist is crystal clear, but it is probably not an impact in the news every day. In short the problem as far as we know it consists of a worldwide insect population collapse. While it is unknown how much of this collapse is caused by human produced and sprayed poisoning by insecticides and herbicides, by habitat destruction or by rising temperatures and haphazard droughts and rain, we are in the middle of a biodiversity collapse at least partly caused by climatechange.

Click here for a list of sources on less news catching 2023 impact of climatechange

3.3 What do scientists already expect to become reality given current levels of climatechange

Human suffering and death

1. By 2050, over 5 billion people — probably more than half the planet’s population — will be exposed to at least a month of health-threatening extreme heat when outdoors in the sun
2. The “crazy” extreme weather rampaging around the globe in 2023 will become the norm within a decade without dramatic climate action, the world’s leading climate scientists have said
3. If warming reaches or exceeds 2 °C this century, mainly richer humans will be responsible for killing roughly 1 billion mainly poorer humans through anthropogenic global warming
4. Editorial: Rapidly intensifying storms are the climate-driven new normal
5. Home insurers cut natural disasters from policies as climate risks grow

On water and food supply

1. Global heating likely to hit world food supply before 1.5C, says UN expert
2. Iraq’s two main rivers could completely dry up in less than 20 years.
3. Globally, total consumer biomass (all ocean life except algae and plants) in the oceans is projected to decrease by 16.7 ± 9.5% more than net primary production (NPP) by 2090–2099. This means food supply from the oceans decreases

3.4 When increases in intensity keep going on we will see food shortages, increasing fascism, nationalism and war

The grave danger of climatechange is however not the threat of how the hotter temperatures and floods directly endanger humans that undergo these tragedies. The gravest danger to our societies and civilization is probably the threat to our globalized food systems. Our civilization is ultimately built upon food security and thus our ability to grow crops on a large scale, fishery and the availability of water for humans and crops. When crops fail, food gets scarcer and prices go up.

Click here for a list of sources on actual or predicted food and water shortages caused by climatechange and how this lead to war and more fascism

3.5: The reasons why climatechange impacts will get much worse (lagging effects, tipping points and science being too careful)

Most items in the paragraphs above consider impacts already happening. Depending on your knowledge level, climatechange can and will get much much worse: not because we are all doom and gloom, but because of lag effects, tipping-points and because science is too careful not to predict too much doom. In the dropdown below this is underpinned by articles and arguments.

Click here for sources on why impacts of climatechange will be way worse than you might think

If you haven't been living under a rock lately you probably have heard about tipping points.

3.5 A: Climatechange has a large lag effect: energy already in the earth climate system has not expressed itself into impacts: but those impacts are already baked in

Lag Effect. Climatechange has a huge and long lag-effect: this means that if we see such extreme effects of it in 2023 and we would stop emitting CO2 (which we won’t, mainly because of politics) the effects will keep getting worse for years to decades. It is important to understand that we have already “dialed in” so much heat into the earth system, climatechange will keep worsening for a long time: even if we really start to smoke out big-oil and all the politicians it has bought and persuaded in every country of the world.

Some articles that describe this:

1. Climate conference hears loss of Arctic summer sea ice now inevitable by 2050
2. James Hansen: There Is a Lot More Warming in the Pipeline and Biggers science story of the week youtube
3. Major sea-level rise caused by melting of Greenland ice cap is ‘now inevitable’
4. Sea-level rise: West Antarctic ice shelf melt ‘unavoidable’

3.5 B: Climatechange will likely proceed by crossing irreversible tipping points causing worse impact and acceleration. Many tipping points are not reversible: once crossed there is no going back

Source of image here

Tipping points cause climatechange’s (largely unknown) non-linear properties. Most likely climatechange will not gradually worsen. It will worsen suddenly, worsen gradually again for a while and then suddenly worsen greatly again and so on. This is caused by tipping points that suddenly change the whole system. That tipping points will occur is partly predictable, but when and how they will alter the climate system is not. Take for instance the warming of the poles. Science has predicted that warming earth temperatures would lead to less ice. But science did not predict this would cause the jet-stream to start wobbling, which in turn accelerated ice-melting on the north-pole because warm blobs of air suddenly could move from south to north, which they did. So suddenly ice-melting became faster than predicted and the poles warmed up much faster than predicted.

Tipping points are often also irreversible. This means that if we stop emitting CO2 tomorrow, and after that even lower CO2 levels, a tipping point like the Amazon dying off, will not reverse. This may produce a different climate system as the one we had. Nobody can predict these things for sure. A dying Amazon forest might never return or if the AMOC stops, it will never start again and the climate in Europe may change for centuries even if climatechange is halted.

For those who want to read more here are some pointers about various tipping points:

1. Exceeding 1.5°C global warming could trigger multiple climate tipping points
2. AMOC. Observation-based early-warning signals for a collapse of the Atlantic Meridional Overturning Circulation
3. See ice extends diminishing
4. Antarctica risks ‘cascades of extreme events’ as Earth warms and Runaway W. Antarctic ice sheet collapse not ‘inevitable’: study
5. Rising methane could be a sign that Earth’s climate is part-way through a ‘termination-level transition’
6. Amazon rain forest degradation and deforestation endanger the South American monsoon and
7. Tropical forests are approaching critical temperature thresholds, and
8. Extreme Australian bush fires pose serious threat to global climate, scientists warn
9. Could Subsea Methane Hydrates Be a Warming “Tipping Point”?

3.5 C: Climatechange will likely proceed faster than predicted because science is too careful

The IPCC has predicted for instance how fast climatechange would cause see levels rise. However, their predictions over the years have become more extreme in the sense that what was formerly predicted as a worse case scenario has been replaced by a more extreme scenario.

Science is by nature prone to predict only what its models can model. And since tipping points are not modeled yet, their effect is not taken up in IPCC scenario’s. This is why IPCC scenario’s are way too conservative in their predictions of impacts of climatechange. When scientists say “impacts are off the charts” and “we are on unknown territory " they are effectively saying “we cannot predict climatechange very well”.

And they can’t because of the scientific method they are currently using for predictions of a system they do not understand (because nobody does at the moment). But this means many of the possible worsening of climatechange are not on the table of political decision makers (not that it would make a difference probably, he said cynically).

A paper predicting how science is much to conservative and predicting way worse climatechange:

1. The planet is heating up faster than predicted, says scientist who sounded climate alarm in the 1980s
2. The paper can be found here. Global warming in the pipeline

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What Stratospheric aerosol injection (SAI) is and what it can deliver and how fast

Wikipedia explains how stratospheric aerosol injection (of sulfur particles) is a form of SRM or Solar radiation modification. In effect stratospheric aerosol injection (I will call it SAI form now now), blocks sun rays from entering the atmosphere.

SAI will diminish further warming of the atmosphere and oceans immediately, because it filters heat (well sunlight) coming in. Why is SAI a near ideal solution at this time:

1. Unlike other unproven forms of geoengineering SAI actually works fast and significantly. There is no doubt SAI will cool the earth: Scientific data from volcanic eruptions proofs this beyond any doubt. Also in the numerous papers mentioned in this blog that feature simulations with SAI the mechanism is never doubted at all. For instance (Lohmann et all 2023) show how historical volcanic outbursts have caused cooling because of massive sulfur emissions.
2. It works right away. From the moment it is used it will work and atmospheric cooling begins: only because of safety reasons implementation will probably begin at a reduced speed. So we can cool the earth in a year or a few years if less speed is desired in the design of the implementation. For instance this paper from 2023 shows how scientists use modelling to determine where and when how much aerosols (well the precursors of them) should be dispersed in the atmosphere to reach specific effects. If you read this paper you will find how in a period of 5-10 years earth temperature can be slowly brought back half a degree, while ensuring cooling down is managed in such a way that for instance the monsoons are not disrupted. Compare this with CO2 removal (CDR): this takes decades to do anything at all (wikipedia tells as of 2023, CDR is estimated to remove around 2 gigatons of CO2 per year, which is equivalent to 4% of the greenhouse gases emitted per year by human activities). So CDR (carbon dioxide removal) takes decades to make a dent in CO2 emission reduction.
3. It is (relatively) cheap. I’ve heard people arguing geoengineering will make big corporations even richer. But in comparison to CDR, the costs of SAI are insignificant (200 million - 1 billion per year). Big oil companies will profit from CO2 removal into gas-files, not from SAI. Sovacool (2021) in paragraph 4.2 describes the costs of SAI (200 million - 1 billion) versus the costs of a full geoengineering solution (100 billion), versus what mitigation of climatechange will cost (100x more = 1000 billion)
4. It stops working really fast again also, which is a great thing: should we inject too much it will disappear in just a few years

The Intergovernmental Panel on Climate Change concludes that SAI “is the most-researched [solar geoengineering] method, with high agreement that it could limit warming to below 1.5 °C (2.7 °F).”

The image below taken from Irvine (2009) paper illustrates what SAI can do: the four graphs show different SAI scenario’s. As you can see in the first graph (a) all cool the earth. Graph B and C show how the scenario’s differ in specific variables like inter-hemisphere temperature gradient or equator-to-pole gradient. The D graph shows how much rain will fall under the different scenario’s.

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The risks of SAI and howto deal with them

This blog argues SAI risks are relatively small. Is that actually true and to what extend? And while I do think SAI is inevitable (if we want to keep a livable earth) I do not think it has no significant risks at all.

Below I will list a long list of risks that are commonly stated in various places, categorized in Governance risks, escalation risks and risks to the climate system. However, to make these risks manageable, rather than just a big pile of discouraging FUD, I will do so by viewing SAI as a global project. Lets envision a global SAI project with a good risk management section. In this way we can address every risk and attach risk management actions to each risk. This will clarify what risks are inherently unsolvable and can’t be mitigated, but also what risks can be mitigated (which of course will take time and effort.) In this way we circumvent the primal human emotional reaction to simply avoid all risks by considering them unmanageable and without looking for solutions to manage risks.

So what risks are there to SAI? A good primer on SAI risks is this blog / article by Yale environmental review. It cites good resources, being firstly Reckless or righteous? Reviewing the sociotechnical benefits and risks of climate change geoengineering (may 2021) and also The Ethics of Geoengineering: A Literature Review (article from 2020). These two articles in their turn provide us with more citations, which help to clarify risk factors.

Drawing from the above sources lets make our risk list and fill the project with tasks.

5.1 Governance risks

Governance risks are risks about the issue how mankind should implement a decision making and implementation structure to make sure balanced and fair decisions are taken.

This risk can be managed by establishing a treaty in an international coalition.

Read more on managing governance risks of SAI

5.2 Social escalation risks Apart from the governance risks of setting up an SAI project, so to speak, there are what I would call the “social escalation” risks (or political if you like). Some scientific papers cite these risks without any referral to how they can be managed. For instance Keys at all (2022) in their paper Potential for perceived failure of stratospheric aerosol injection deployment describe how, even if SAI would lower global temperatures, specific areas due to local climate could still get hotter, and present a model that produces such a state of affairs. After pointing out this risk this paper seeks to manage this risk by a calls for more research into SAI, but also by a forward thinking SAI research agenda.

As I see it, again implementing a fair treaty is the most important step when mitigating social escalation risks.

Read more on managing social escalation risks of SAI

5.3 Climate risks as in risks to the climate system The set of risks most often cited, even a lot more than governance risks, are risks SAI might have for the climate. Often these risks are deemed so large we should never begin with SAI unless in dire need because of climate change

But as you may have red, I don’t think FUD (fear uncertainty and doubt) should cloud this discussion. Lets get serious and name those risks. And yes compare them to the current and near-future climatechange risks. As also stated in the intro, this is important since our human brains are very good in noticing danger (risks) and reacting to it, but not good at all for dealing with risk (Behavioral science has numerous books and articles like this online blog Our Brains Were Not Built for This Much Uncertainty explaining why). Because we are not very good at comparing risks, those arguing against SAI often cite the dangers of it, and also acknowledge the dangers of climatechange. But choosing between two evils is not often done. But I argue we must, because in our current world choosing against SAI is choosing to accept already locked-in ongoing climate change (given insufficient action to curb emissions).

While reading a great number of papers I have distilled these risks:

1. SAI can cool down the world, but some parts of it can still get hotter or monsoons might stop
2. SAI will cool the climate but sea level rise will not stop.
3. SAI will cause drought because there is less rain
4. SAI does not lower CO2 and therefore ocean acidification will keep on getting worse
5. When SAI is stopped while CO2 levels are high, earth will get a heat shock and will warm up very quickly

Please drop me a note if you have found another risk I can include in this blog. But let’s dive in and see how big these risks are and if we can manage them in a relevant way.

1. Perceived risk to climate system: SAI can cool down the world, but some parts of it can still get hotter or monsoons might stop Early modelling of SAI has brought up fears that SAI implementation will help cooling down the earth in some places, while causing negative results elsewhere.

The studies mentioned in the drop-down below show how progress is made in reaching optimal SAI scenario’s through more research and how a finding a design that does not overly harm specific regions is probable. Studies seem to point toward research on scenario’s where not all warming is compensated for by SAI. In the current scientific simulation papers a need for further improvement is noted: better predictions might be possible if more detailed simulations can be run. Given the impact of the monsoon risk, improving research seems sensible. It also seems sensible to let the Indian region decide when predictions are accurate enough to start SAI with, yes or no.

Read (a lot) more on the SAI Monsoon risk

2. Perceived risk to climate system: SAI will cool the atmosphere but sea level rise will not stop entirely.

This claim is true but it is also true that SAI will stop most relevant sea level rise. As Irvine et all (2012) shows, sea level rise will be stopped at 30cm rise or less in the period until 2100.

Read more on SAI and sea-level rise

3. Perceived risk to climate system: SAI causes drought because there is less rain If the earth cools off again, because of SAI, rainfall will again be less catastrophic, because colder air can hold less water. (I will use the word rainfall to refer to all kinds of precipitation, so rain and snow and so on)

However even if rainfall diminishes somewhat, it will still stay on par with levels reached between the years 2000-2010. SAI will cool off the earth somewhat, but won’t cool it down below levels before climatechange began.

Read more on SAI and rainfall (precipitation)

4. Perceived risk to climate system: SAI does not lower CO2 and therefore ocean acidification will keep on getting worse

Ocean acidification is when CO2 in the atmosphere keeps rising and the PH of ocean water lowers because of CO2 uptake. When SAI is used to lower global temperatures this does nothing to lower CO2 levels, and so if CO2 keeps rising we may have a cooler earth, but ocean acidification keeps rising. This is true of course. For a short explanation see this short film explanation
https://oceanservice.noaa.gov/facts/ocean-acidification.mp4

Ocean Acidification (OA) is very complex. I have compiled a rather large text on OA at the end of this blog, including many recent scientific resources. Here I will only show the conclusions.

Read more on managing SAI and ocean acidification (OA)

Conclusion: Ocean Acidification and SAI

OA of course is result of rising CO2 levels in the atmosphere. The specific risk SAI brings in this regard is that the urgent calls to reduce CO2 emissions may / will fade when SAI takes away many problems caused by climatechange. This risk can of course become reality easily enough. Therefor a treaty on SAI deployment must include bringing down CO2 emissions, as stated earlier. Ocean acidification is a real danger to both ecosystems and humanity: on the other end OA will probably play out slowly and there is quite some time before its impacts really become dire.

5. Perceived risk to climate system: When SAI is stopped while CO2 levels are high, earth will get a heat shock and will warm up very quickly

This of course is true: when CO2 levels are very high, but the earth is cooled by SAI, temperature will be much lower then without SAI. If SAI is then stopped aerosol particles will naturally diminish, and heat will go up in a year or two.

The risk here is probably best described as the risk of how human society can become so unstable it stops implementation of SAI while CO2 levels are still too high. Mitigation of this risk lies in a stable governance: All the more reason to have a treaty in place to legitimize SAI, that makes sure SAI is not stopped unless CO2 levels are below a safe level.

In my view this risk is minor.

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6 Conclusion and who wrote this

The conclusion of this blog is of course what the beginning tells you, since not many people will read all the way until the end:

1. Climatechange is madly out of control and the level of panic is way too low. Scientists are grieving and mourning and we are really living the movie Don’t Look up.
2. Humanity has a solution that can stabilize the climate right away. To deploy SAI an international treaty is needed where many thing must be overcome (see the beginning of this blog). We should start experimenting with stratospheric aerosol injection tomorrow or rather last year and improve simulations to manage the larger real risks (like stability of the monsoon)
3. At the moment, there isn’t a real discussion on SAI, probably because people can’t grasp how deep in climatechange shit we really are, but also because no serious risk analysis is taking place by governments or the IPCC. The lack of a serious risk analysis feeds FUD on SAI and is in the way of a proper scientific discussion.

Climate change disaster can be avoided by SAI and it is our duty to protect the next generation.

Who wrote this blog.

Hans-Cees Speel is a father of 55 years old with two children he would like to see having a future. He has a university degree in both Ecology and Environmental sciences (Natuurwetenschappelijke Milieukunde in Dutch) and is a risk manager in IT (CISO). His Crappy website is here His website on European trees can be found here

Please post your feedback on this blog on mastodon aimed at Hans-Cees

https://en.wikipedia.org/wiki/Biological_pump#/media/File:Oceanic_Food_Web.jpg

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7. Several rebuttals of arguments against stratospheric aerosol injection

When discussing SAI online (aka on mastodon mostly) many false arguments are brought to bear on why SAI should not be implemented. Even people warning that SAI is genocide. These arguments are probably made by well-meaning individuals that do not want our earth to be abused. That may be so, but they blind a real discussion.

Therefore I have compiled a list of rebuttals to often heard argumentation against SAI that sound right, but are misguided.

Rebuttals of false arguments against SAI:

1. SAI is geoengineering and that’s dangerous, we shouldn’t start with geoengineering. Climatechange as it exists today has been one big geoengineering experiment all along. We as humanity have caused climatechange by knowingly or unknowingly implementing geoengineering (adding CO2 to the atmosphere). You cannot argue we shouldn’t start to use geoengineering, when we are already doing that. Climatechange is also geoengineering and SAI will counter the harmful effects of climatechange. Humanity has caused problems and should solve them as well.
2. SAI is the wrong solution, we should stop emitting CO2 and other gases. This argument is really false: that one solution is right does not mean the other is automatically wrong. Reducing greenhouse gases is the only lasting solution to climatechange: that is true. But cutting emissions takes far too long to protect the earth climate system right now and it does not stop the already locked in climate change effects. We need multiple solutions at the same time
3. If we start SAI right-wing people and oil companies won’t cut back emissions because they will have an excuses not to. Well this is of course a real risk. But this risk is already a big problem of course, also without SAI. So this risk will stay a constant problem we will have to deal with anyway. However, it is highly unethical to not use SAI and counter harmful effects of ongoing climatechange because of what oil companies say or do: they are evil either way. We should do what is good for humanity and ecosystems: and that is start negotiating and planning SAI right away. I think the majority of humanity wants to get rid of oil and fossil fuels and the movement toward sustainable energy is unstoppable: it just takes long.
4. We don’t need this dangerous SAI / geoengineering, because as climatechange gets worse people will start cutting back emissions faster and that is what we really need. Again we are already geoengineering and its gone horribly wrong, we should correct that. Beside that point already made above, people won’t start cutting back emissions when things get worse. If we learn from history, when things get bad (hunger strikes, prices sore), people will vote for “strong leaders” and these leaders will simply deny climatechange exists and more likely start wars and will certainly let the most vulnerable people starve. Since Trump sand Brexit we know what insanity politics produces when it is in bed with big-oil. If climatechange worsens likely emissions won’t go down at all: we need a world without constant disasters to solve this problem, and therefore we need stability and strong democracies. SAI can give time to cut back on emissions in a relative stable world.
5. SAI will start an ice-age and has caused mass die-outs in history: its just too dangerous. Won’t SAI cause an ice-age? Well no, because unlike unchecked vulcanism, we can be very careful how to implement SAI. With the human monitoring capabilities using satellites and so on, we can monitor how much aerosols where and when have what effect. For instance this paper from 2023 shows how scientists use modelling to determine where and when how much aerosols (well the precursors of them) should be dispersed in the atmosphere to reach specific effects. If you read this paper you will find how in a period of 5-10 years earth temperature can be slowly brought back half a degree, while ensuring cooling down is managed in such a way that for instance the monsoons are not disrupted.
6. Climatechange was caused by putting chemicals in the atmosphere, and SAI is more chemicals, so that is extremely dangerous and we shouldn’t risk that. If you think about this kind of reasoning its like saying: “Look, we have these children in this room and we took their food away and now they are crying from hunger. So someone wants to go in the room to bring them food, and you say “no don’t bring them food, its messing with food that started all this”. This argumentation is nothing but misguided fear, ignoring how the impact is totally different and also ignoring our responsibility to make right what we did wrong.

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8. Extra research on Ocean Acidification

This part is the background information underlying the conclusion about ocean acidification (OA): SAI does not lower CO2 and therefore ocean acidification will keep on getting worse

Ocean acidification is when the PH of ocean water lowers because of CO2 uptake. When SAI is used to lower global temperatures this does nothing to lower CO2 levels, and so if CO2 keeps rising we may have a cooler earth, but ocean acidification keeps rising. This is true of course. For a short explanation see this short film explanation
https://oceanservice.noaa.gov/facts/ocean-acidification.mp4

Worries are that a lower PH will wreak havoc on ecological networks because every organisms in the ocean that uses calcium might die out or become less prolific: shellfish, clams, A host of information is available on this website by NOAA PMEL carbon program.

However, as often with scientific research on biological earth cycles: it is much more complicated and things are not what they seem to be. To explain the broad picture I will need a lot of text I am afraid. To make all this insight manageable I will break up the text below in parts: 8.1 Ocean Acidification (OA): what is it and some oceanography? 8.2: Ocean Acidification (OA): what risks and how big are those risks

Ocean acidification (OA): what is it and some oceanography

Essentially as CO2 levels in the atmosphere rise, more CO2 gets dissolved in the ocean. Now dissolved CO2 in the ocean does not stay CO2 but reacts with water molecules and other chemicals. The processes involved are pretty complex as pretty well explained by Paul Webb here on the website on Carbon Dioxide, pH, and Ocean Acidification. In short: the more CO2 in the atmosphere: the lower the PH of the ocean gets.

Now because may ocean organisms have skeletons partly based on calcium-carbonate, and calcium carbonate minerals (calcite and aragonite) dissolve when put in acidic water, it is feared that ocean acidification can wreak havoc on oceanic life and also particularly on food-chains humanity depends upon. Since the first alarm-bells on OA went off about 2005 however, the risks of OA seem to diminish somewhat, but also still more facts and insights are emerging from research into these matters today (2023 as I write this).

The deeper you get the more dissolved CO2 But before delving into the risks in detail: some context on CO2 and calcite in the oceans. Very bluntly put: the deeper you get into the ocean, the more CO2 is dissolved in water and the less (solid) calcium-carbonate particles are found in the water and in the sediment (the ocean floor). This mainly has to do with the temperature of water: more gasses will dissolve when its colder and they will “boil” out of it when it gets hotter, just like water will become vapor when boiled (I know the explanation isn’t perfect, but for most readers this will drive the point home). So colder water means more dissolved CO2. But more CO2 dissolved also means the water becomes more acid (PH goes down). Now if the PH goes down, calcium-carbonate will start to dissolve (because of chemical / physical forces).

Coastal plane, deep sea and phytoplankton Now the oceans of course have different depths: broadly near shore there is a coastal plane that is not very deep (well, upto 300-400m, which is pretty deep with your snorkel [pun intended]) but compared to the deep see, which can be 5000m the coastal plane is not deep. The ocean floor where it is deep is called the benthic zone : it is also the largest ecosystem on earth, of which humanity knows surprisingly little (because its hard to get that deep under water and stay alive and also its pitch-black). Now like on land ecological food-chains always start with the energy of the sun being fixed into sugars by mainly green organisms (by photosynthesis) we call plants and algae. Now on land most photosynthesis is carried out by trees in forests (if there’s enough water for them to grow): not so in the sea. In the sea organisms do not need wooden structures to be closest to the light: algae just float on the water. So in the ocean photosynthesis is not carried out by large plants but mainly by very small organisms we call phytoplankton. The growth of this phytoplankton is limited by both nutrients but even more so by zooplankton: lets say organisms that eat the phytoplankton (of course its more complicated, read more about plankton here). We are always told trees give us oxygen (which is true), but phytoplankton produces a lot more oxygen than trees do (so before you think who cares about this sea stuff..: humanity depends on it).

The biological pump: sinking biological matter including calcium-carbonate particles

Image showing biological pump, see wikipedia

Back to Ocean Acidification: much of the plankton lives in shallow water: since below 500-1000 meter there is no light anymore so no phytoplankton can grow there. So there’s a whole lot of microscopic life going on in the most upper layers of the oceans. Now many plankton species have calcium-carbonate structures: calcium-carbonate is firstly used like turtle shells: it can protect you from being eaten (bivalves like mussels use their shell in that way) and secondly calcium-carbonate functions to strengthen organism (much like bones do) as well. All this teeming life in the upper ocean layer thus collectively produces calcium-carbonate structures big and small. And as zooplankton eats phytoplankton and bigger organisms eat zooplankton again, a lot if these calcium-carbonate structures end up inside droppings or feces. These droppings, together with simple deceased plankton organisms slowly sink to the bottom of the sea and therefore a lot of calcium-carbonate along with other biological carbon is buried in the sea-floor. There is a name for this ocean phenomenon: the biological pump. Also, specific species like krill actively play a role in the biological pump, because krill species eat during the night in shallow water, then by day migrate to deeper water, where they digest and produce droppings deep in the oceans. As Wikipedia states: The biological pump (or ocean carbon biological pump or marine biological carbon pump) is the ocean’s biologically driven sequestration of carbon from the atmosphere and land runoff to the ocean interior and seafloor sediments.[1] In other words, it is a biologically mediated process which results in the sequestering of carbon in the deep ocean away from the atmosphere and the land.

Acidification: depth and calcite saturation levels Above I explained how colder and deeper water has more dissolved CO2 and thus is more acid which makes calcium-carbonate dissolve. With the CO2 levels of the last 65 million years (until now) this adds up to an ocean where:

1. The shallowest and thus warmest layers of water are saturated with aragonite and calcite and the layers below it only with calcite. “Saturated” here means that calcium-carbonate particles will naturally grow bigger, because calcium-carbonate particles in the water will naturally deposit on it. This makes it a good environment for organisms with shells and other calcium-carbonate body-parts
2. Below a certain depth, as water gets colder and thus more acid, water is called “unsaturated” and calcium-carbonate structures will dissolve. In this depth organisms with calcium-carbonate body-parts can still exists, but maintaining them costs more energy and not all species can live here.
3. Everywhere in the oceans we have this carbonate-rain, remember the biological pump? Now below the depth where water gets unsaturated (and this depth differs as water temperature differs) calcium-carbonate does sink to the bottom, but it also slowly dissolves once it is on the bottom. This means that deep water floors have very little calcium-carbonate in them. Above the depth levels where water becomes saturated calcium-carbonate quickly becomes the main ingredient of the sediment.

Sulpis et all (2018) has some nice graphical material to show this

Atlantic Ocean sediment calcite content profiles and calcite marker horizons. Calcite fraction in dry sediments (Xcalcite), ±1 SD, for the basins defined by the maps below the plots. The number of measurements (n) comprised within each basin is also reported. The preindustrial calcite compensation depth (CCD) and saturation depth (CSD) are represented with dashed horizontal lines (on the Left of each profile), whereas the solid horizontal lines correspond to current values (on the Right of each profile). Both the CCD and CSD are reported along with their uncertainties.

How does acidification fit in? Sulpis (et all 2018) show how all carbonate matter starts to dissolve into the ocean below the level where undersaturation first occurs: the calcite saturation depth (CSD): below this depth calcite levels in the sediment decrease. Secondly they define the depth where the deposition rate of CaCO3 is exactly balanced between calcite deposition and dissolution as the calcite compensation depth (CCD): at this depth calcite levels stay the same. Thirdly the “snowline” is defined as the depth where the calcite (CaC03) part of the sediment falls below 10%. When CO2 concentration in the air rises (as with climatechange at the moment), water gets more acid and the CSD shallows. Below the CSD calcite in the sediment starts to dissolve and calcite fractions get less. However, it takes quite some time for calcite to dissolve as the rate of dissolving is foremost dependent on the movement of he water directly above the sediment (as Sulpis proves).

In the graphics from the Sulpis paper it is visible where acidification has already effected the oceans: mostly in colder waters just south of Greenland. Ocean acidification and bottom-water [CO32−]SW decrease. (A) Preindustrial bottom-water [CO32−]SW, (B) current bottom-water [CO32−]SW, and (C) difference between preindustrial and current bottom-water [CO32−]SW (Δ[CO32−]SW = current bottom-water [CO32−]SW − preindustrial bottom-water [CO32−]SW), below 300 m. Uncertainties are indicated by the red outline on the color bar, corresponding to 1 SD of 16.9 µmol⋅kg−1 for Δ[CO32−]SW.

This graphic shows how deep the saturation zone is where in the oceans and also how much calcite is dissolved currently Chemical and physical parameters for calcite dissolution. (A) Overall mass transfer coefficient k for CaCO3 dissolution, (B) current bottom-water saturation concentration [CO32−]eq at in situ temperature, salinity, and pressure, and (C) present-day calcite compensation depth (CCD), regionally averaged as described in Materials and Methods, where the light gray identifies areas where the CCD is deeper than the depth of the seafloor, that is, where calcite can undergo net sediment accumulation. The CCD is not computed in the Arctic and Southern Oceans (south of 60°S).*

When will ocean acidification take place? Before we will start to look at the risks of OA, lets see when OA will become a significant factor.

In the same special issue of Oceanography of the Kump paper above “The Future of Ocean Biochemistry in a High-CO2 World (2009)” Feely at all, write:

The model projections indicate that aragonite undersaturation will start to occur by about 2020 in the Arctic Ocean and 2050 in the Southern Ocean. By 2050, all of the Arctic will be undersaturated with respect to aragonite, and by 2095, all of the Southern Ocean and parts of the North Pacific will be undersaturated. For calcite, undersaturation occurs when carbonate ion concentration drops below 42 µmol kg-1. By 2095, most of the Arctic and some parts of the Bering and Chukchi seas will be undersaturated with respect to calcite. However, in most of the other ocean basins, the surface waters will still be saturated with respect to calcite, but at a level greatly reduced from the present.

I have searched for other reports if those estimates might have changed between 2009 and 2023 in scientific papers, but haven’t found indications of a slowdown because of new insights for instance. Searching through many papers on OA it does become clear how different parts of the word will see a faster or slower OA impact.

Gruber at all (2012) ran models and these predict how under CO2 ppm values of 541 (A2 SRES scenario) in 2050, the annual mean aragonite saturation horizon (in the Californian ocean system) is as shallow as 100 m in the offshore region, but shoals to less than 50 m in the nearshore regions in the annual mean. In the summer, the aragonite saturation horizon breaks to the surface in many parts of the central California CS (fig. S4). Thus, ocean acidification will severely reduce the habitat for organisms that are sensitive to the saturation state, and particularly for those who cannot tolerate undersaturated conditions for an extensive period of time. Within the next 20 to 30 years, the volume of undersaturated waters quickly expands, and by around 2035 in the SRES A2 scenario, nearly the entire twilight zone of the central California Coast will be undersaturated year-round (…) The projected evolution of the upper ocean in the nearshore 10 km of the central California CS toward low Ωarag conditions is similar to that projected for the Southern Ocean and the Arctic (Fig. 3), which previously have been proposed as the first oceanic regions to become undersaturated (9, 18). The upper twilight zone and the bottom layer of the central California CS become undersaturated even faster than the surface Arctic, highlighting the imminent nature of reaching this threshold

So if Gruber is right “the twilight zone” part of the ocean (60-500 meters of so) in California will be significantly impacted by OA within a decade or two, since aragonite undersaturated waters (where it will cost organisms more energy to maintain their bodies) will be present year-round. Remember how aragonite is one of the two important calcium-carbonate minerals commonly used by many ocean species.

Xu et all (2023) describe how aragonite rates in a Chinese estuary vary over time and also:

1. how up-welling deeper water has little aragonite and lower temperatures cause lower aragonite levels
2. how stratification takes place, where deeper colder water has less aragonite and top-level warmer water has more aragonite
3. how aragonite levels thus variate considerably throughout the year
4. how incoming river water usually has lower aragonite values than sea water
5. Aragonite decreases if oxygen-consuming processes dominate (respiration) and increases when photosynthesis dominates
6. coastal acidification may occur more rapidly than that in the open ocean, with considerable variability and complexity

Both Xu and Gruber show how there is a great variety in timescale when OA will become impactful on ocean eco-systems. The levels of the different chemicals involved in OA vary and fluctuate depending on many factors like water temperature, the amount of calcium-carbonate in the sediment (lower in Pacific and higher in the Atlantic ocean), currents with different levels of chemical and estuaries where water from rivers mingles with sea water.

OK, so the impact of OA will vary according to the specific region where (ant)arctic colder waters are hit earlier and also pacific waters will generally suffer OA earlier than Atlantic regions. The first significant events are estimated to start happening between now (2023) and 2035. The first impactful event being “twilight-zone waters year-round undersaturated by aragonite”. Why is that significant:

1. Firstly because most biological ocean production takes place in the upper layers of the ocean (remember the floating phytoplankton)
2. And secondly because this production for a significant part also takes place above the continental shelve parts of the oceans
3. Thirdly because many coral-based ecosystems function as the nurseries of many species. And since coral exists of creatures excreting calcium-carbonate which forms the reefs, impact of OA on the nurseries might possibly be large. Lefcheck et all (2019) conducted a meta-analysis on the nursery function in the oceans and conclude Our results confirm the basic nursery function of certain structured habitats, which lends further support to their conservation, restoration, and management at a time when our coastal environments are becoming increasingly impacted.

Ocean acidification (OA): what risks and how big are those risks

The risk of OA depends of course on what impact it will have on the current state of:

1. Ecosystem services: things like:
   1. Oxygen produced by phytoplankton in the oceans
   2. Harvested fish and other seafood for consumption
   3. Value generated by tourism
   4. Carbon burial in the ocean floor and carbon take-up in the ocean
2. Intrinsic values of oceanic biodiversity and life

There are many studies reporting possible impact on specific oceanic processes. To name a few:

James et all (2017) experiment with plankton communities trying to assess how these will react to OA but also write: How this broad range in the frequency and magnitude of elevated pCO2 exposure impacts DOC processing by bacterioplankton remains largely unknown. DOC stands for dissolved organic matter and a hypothesis is that higher acidification could lead to less C burial in ocean floors, thus forming a positive feedback on CO2 levels.

Sulpis (et all 2018) show how OA leads to weathering of ocean floor calcium-carbonate thus forming a negative feedback on CO2 levels in the atmosphere. The dissolving process produces more calcite matter in the water, which counteracts the acidification. This is essentially the same process as weathering, which is also a negative feedback on rising levels of CO2.

Ravaglioli at all (2020) show how ocean acidification alters meiobenthic assemblage composition and organic matter degradation rates in seagrass sediments.

Tagliabue at all (2021) reports how Persistent Uncertainties in Ocean Net Primary Production Climate Change Projections at Regional Scales Raise Challenges for Assessing Impacts on Ecosystem Services. and if this is coupled to Stock et all (2017) that report about Reconciling fisheries catch and ocean productivity, the conclusion is there is currently no general understanding how ocean food-webs work in a quantitative way.

Nagelkerken and Connel (2015) performed a metaanalysis of 632 published experiments and quantified the direction and magnitude of ecological change resulting from ocean acidification and warming to conceptualize broadly based change. They conclude Primary production by temperate noncalcifying plankton increases with elevated temperature and CO2, whereas tropical plankton decreases productivity because of acidification. Temperature increases consumption by and metabolic rates of herbivores, but this response does not translate into greater secondary production, which instead decreases with acidification in calcifying and noncalcifying species. This effect creates a mismatch with carnivores whose metabolic and foraging costs increase with temperature. Species diversity and abundances of tropical as well as temperate species decline with acidification, with shifts favoring novel community compositions dominated by noncalcifiers and microorganisms.

https://upload.wikimedia.org/wikipedia/commons/f/f6/General_characteristics_of_a_large_marine_ecosystem.jpg

However, as with other climate scientific research the overall impact of OA remains unclear: Currently, we have insufficient knowledge to predict confidently the future impacts of ocean acidification on marine organisms and ecosystems writes Kump et all (2009, Ocean acidification in deep time) in a special issue on OA. They write how in the past geological timeline there have been times with high CO2 levels where nevertheless calcium deposits are found (suggesting see creatures could build calcium based structures). But they also warn that in times of fast CO2 level fluxes mass-extinctions took place, suggesting species cannot adapt quickly to CO2 level and/or temperature changes thus causing mass-extinctions.

My conclusion after reading scientific papers on OA is there is at this moment (2023) no general conclusion or prediction what impact OA has or will have. This is probably because current studies look at climate change as a package of both warming and acidification and do not consider acidification alone. For instance Luzinais et all (2023) compute how primary production (in the ocean) changes from +5% to -5% until 2100 in comparison to the last 20 years if climatechange progresses as it does now. However, consumer biomass (fish and all living forms in the sea except phytoplankton), will probably shrink by 5 to 25% until 2100. I have until now not found any studies that project this in an situation where oceans do not warm up, but that do leave acidification in place as a variable.

So if there are no quantitative studies projecting OA under a SAI scenario, what will OA probably do qualitatively? Can we take a guess? We can of course try. Firstly we know OA will hit different parts of the oceans in different timescales. The impact will start in the pacific oceans and in the arctic and antarctic oceans within 20 years. before 2100 (in 80 years) all oceans will feel the impact (according to the studies above) The qualitative effects will probably include:

1. What will happen if the ocean becomes more acid? Well we know firstly aragonite will become undersaturated and later on calcite Figuerola at all (2021) A Review and Meta-Analysis of Potential Impacts of Ocean Acidification on Marine Calcifiers From the Southern Ocean.
2. Secondly this will happen at different times in different parts of the oceans as explained above, cold waters and Pacific oceans first, Atlantic ocean later
3. While many species with calcium-carbonate structures can probably take some acidification, it will cost them more energy and so in ecological webs species will be out-competed or really die out. Some may also evolve into species with less structures or other mineral composition in their structures, especially species with many generations in a short time. See Stanley and Hardie (1998) for a study on reef forming species and mineral changes in the Phanerozoic Eon
4. Specific structures like coral reefs may completely disappear, especially in cold waters. Coral reefs do have an ecological function as nurseries for fish, but there are many other nurseries besides coral reefs (TODO find ref)
5. Some fish larvae are impacted by OA, for instance growth rate may diminish, but the level of impact will probably vary between species and individuals. See for instance Siegfield and Johnson (2023)
6. Climate change will alter biomass production in the oceans. I already mentioned how Luzinais et all (2023) compute how primary production might change from +5% to -5% until 2100 and consumer biomass will probably shrink by 5 to 25%. Above I already wrote how I have not found studies that project this in an situation where oceans do not warm up, but that do leave acidification in place as a variable. But I did find studies on krill: a number of species of small crustaceans (shrimp-like) that produce a significant biomass in the oceans and especially in the ocean around the south pole (the southern ocean) are a key-stone species. Key-stone species are species that characterize an ecosystem because of their important role. In the southern ocean krill is the main species that eats the phytoplankton (algae and so on) and in its turn krill is eaten by the typical species of Antarctica like seals, seabird, fish, whales, penguins and so on. Kawaguchi et all (2010) showed how the larvae of krill won’t develop properly if acidification ramps up. No significant effects were detected on embryonic development or larval behaviour at 1000 µatm pCO2; however, at 2000 µatm pCO2 development was disrupted before gastrulation in 90 per cent of embryos. (…) Model projections demonstrated that Southern Ocean sea water pCO2 could rise up to 1400 µatm in krill’s depth range under the IPCC IS92a scenario by the year 2100 (atmospheric pCO2 788 µatm). Rowlands at all (2021) found that a combination of acidification and micro-plastics as found in the southern ocean, will hamper development of embryo’s before acidification alone will, pointing to the fact that in real life situations species encounter more negative stressors than only acidification. They also found that at 900ppm no development of krill was hampered yet. So while there probably is an acidification level at which krill populations in the southern ocean will collapse, and with it the entire current ecosystem, it is not clear at what levels of OA this might start to happen. If Rowlands research is right this might be at CO2 levels around 780, which the world may reach already in 2080

Conclusion Studies on OA generally study it as a part of an ocean where also warming takes place. If SAI is deployed, this is not accurate. However, it is clear that unless CO2 levels in the atmosphere stop rising, OA will become a significant force in the oceans, firstly in the Pacific, the Arctic and Antarctic oceans (situations where water is completely unsaturated all year round). This will cause species die-out and specific structures like corals will probably disappear. However, while this means a reshuffle in ecosystems it is not certain / likely this will result in collapse of food-chains or production. It is however certainly possible that specific fish species important for human consumption will vanish and its also possible ecosystem collapse occurs much sooner, because scientific knowledge is lacking. However, with for instance krill we see an example where in 70-150 years ecosystem collapse is probable, causing a significant biomass collapse. And logically these effects are not yet taken into account in the modelling of Luzinais where a decrease of 5-25% of consumer biomass is predicted by 2080 (see longer text below the blogtext).

As for the different risks we started this part of ocean acidification with, we can conclude:

The risk of OA depends on what impact it will have on the current state of:

1. Ecosystem services: things like:
   1. Oxygen produced by phytoplankton in the oceans. We found no papers describing impact on oxygen production by OA (unless krill collapse will lead to algae blooms that cause oxygenation problems).
   2. Harvested fish and other seafood for consumption. We found how krill collapse might cause significant alterations in the southern oceans in 70-150 years. I do not know how this will play out in other parts of the oceans. Specific fish species (perhaps many) important for human consumption may die-out unexpectedly. This has to do with fish-larvae being vulnerable to OA.
   3. Value generated by tourism: collapse of coral reefs will have impact here. But ocean warming might very well wipe them out before OA will (unless SAI is implemented of course).
   4. Carbon burial in the ocean floor and carbon take-up in the ocean. There will certainly be impact here, and certainly when krill populations collapse, because krill plays a significant role in the biological pump.
2. Intrinsic values of oceanic biodiversity and life. Of course OA will cause many species will die out worldwide. It is probable that mass die-out events will take place, because many calcium-carbonate dependent species will be impacted.

So there we have the conclusion: Ocean acidification will within 100 years or so probably cause mass die-out events of many species beginning in the pacific and the southern oceans. After a certain tipping point it is likely krill collapse will have a snow-ball effect in specific oceans, but perhaps other oceans won’t have such a collapse of biomass production. Since acidification is such a systemic factor, it is unlikely these impacts can be mitigated without lowering CO2 levels in the atmosphere.