I recently read this article in Science News and I thought it would be an interesting topic to talk about. I don’t know how much the average person knows about climate engineering, which is a shame because it is a conversation about climate change that scientists and policy makers are starting to have. In theory, it could be part of a solution for climate change, able to undo much of the damage we’ve done to our planet in a short period of time. But among climatologists, it is an incredibly controversial topic with many people calling for it to be restricted, and for some very good reasons. So because this could very well become a hot button political issue in a decade or two, let’s talk about what climate engineering is and its pros and cons.
The Methods
Climate engineering, or geoengineering, is an umbrella term for multiple techniques which we could use to deliberately alter Earth’s climate, specifically to slow or halt anthropogenic climate change. This tends to be divided into two broad strategies; carbon dioxide removal and solar radiation management. Carbon dioxide removal denotes strategies for, you guessed it, removing our carbon emissions from the atmosphere and sequestering it somewhere else. Strategies for this include;
Biological sequestration: Perhaps the most obvious technique, restoring plant life to degraded land would remove a lot of CO2 from the atmosphere. This includes restoring forests, wetlands, peatlands, and prairies, which all naturally store a lot of carbon. Farming techniques have been explored which would sequester carbon in the soil, both removing carbon and improving soil quality. These techniques would have additional benefits to our ecosystem, but they have their limitations due to time and expense.
Biochar: When organic matter is heated to high temperatures but in an environment too low in oxygen for it to burn, this organic matter gets converted into charcoal. Biochar is a particular type of charcoal that has been used throughout history as a soil amendment. You see, healthy soil contains numerous organic compounds which serve a multitude of purposes, from nutrients for plants to pH balancing to preventing soil erosion. When plants die, between 5-10% of the carbon in their bodies is converted into this soil carbon, the rest becoming CO2 in the air. Converting agricultural waste into biochar and then adding this biochar to soil would be a way to convert almost 100% of this waste’s carbon into soil carbon, permanently sequestering it while also improving soil quality and crop yields. Biochar also has potential applications as an additive in asphalt, concrete, animal feed, and plastics. Biochar is a very inexpensive way to sequester carbon, with some proponents suggesting that farmers in developing countries could make money by selling carbon offsets for biochar production. That said, there are limits to how much carbon can be stored in the planet’s farmland and there is conflicting research on just how permanent soil sequestration is.
Direct air capture: Perhaps the most basic, sucking CO2 out of the atmosphere and storing it somewhere else. There are multiple methods of doing this being explored, but the most common is to use giant fans to blow ambient air through an alkali solvent, which absorbs just the CO2 and can release it when heated. This concentrated CO2 can then be compressed and stored like other gasses. What we do with this stored carbon still needs to be determined, with deep geologic sites like former oil wells being a potential depository. But this is still a very inefficient way to sequester carbon, and it would need to be powered by renewables in order to make it remotely useful.
Ocean fertilization: Artificially introducing nutrients to the upper ocean in order to cause algae blooms which would absorb carbon. This one is the most controversial one on the list, as there isn’t enough evidence to suggest this would be effective. Also, these large algae blooms could cause disruptions to marine ecosystems and fisheries. It’s still being researched, but so far this does not appear to be a technique worth pursuing.
I’ve only given a handful of the most well known ways of pulling CO2 out of the atmosphere. Other proposals have been made, such as pumping CO2 into underground deposits of carbon-absorbing minerals or just burying enormous amounts of wood and biochar to remove it from the carbon cycle. While these are all things we should try in order to slow anthropogenic climate change, none of these are solutions that would work in the near term. And to fully discuss climate engineering, we need to talk about solar radiation management.
Greenhouse gasses warm the planet by trapping heat from the Sun in Earth’s atmosphere. Visible light from the Sun passes through CO2 without stopping and warms the Earth’s surface, but when this heat gets radiated back into space as infrared light, CO2 reflects much of this light back to Earth’s surface. The goal of solar radiation management is to reduce the amount of sunlight that makes it to Earth’s surface in the first place, cooling the planet by cutting heat off at the source. Proposals for how to do this include covering large portions of the planet’s surface with reflective materials or putting mirrors in low earth orbit, though both of these strategies would be largely infeasible. A more realistic proposal is marine cloud brightening; wherein sea water is sprayed into the atmosphere as a fine mist in order to brighten marine stratocumulus clouds so they reflect more light back into space. To completely return Earth’s climate to its pre-industrial state would require a fleet of thousands of ships continuously spraying sea water into the air as droplets one-fiftieth the size of naturally forming cloud droplets. This mist would mix with existing marine clouds to make them far larger and the small droplet size would make these clouds more reflective. Using sea water would make the process safe and non-resource intensive and this process has the advantage of being focusable on at-risk regions, such as the Arctic and Antarctic ice sheets. That said, many technologies critical to effective marine cloud brightening are not yet developed enough to be implemented. Specifically, we are not yet able to generate droplets that small en masse or launch them high enough into the atmosphere to have the desired effect. To combat climate change in the near term, we would need something a bit more proven.
This brings us to the climate engineering technique I wanted to talk about most, the one you might have already heard about if you’re at all familiar with this topic. Stratospheric aerosol injection; spraying a fine aerosol into the upper atmosphere in order to partially block out the sun. We know this would work because it happens in nature periodically. Volcanic eruptions launch aerosols (solid particles or liquid droplets small enough to be suspended in air) into the stratosphere and large enough eruptions can launch enough aerosols to significantly alter global climate. 1816 has been called “The Year Without a Summer” due to the cooling effects caused by the 1815 eruption of Mt. Tambora in Indonesia. Less severe but still notable global cooling events occurred in the years following the 1883 eruption of Krakatoa and in the “Summer that Wasn’t” following the 1991 eruption of Mt. Pinatubo in the Philippeans. The goal of stratospheric aerosol injection is to create a volcanic winter like these, but controlled and precise enough to offset the warming caused by climate change.
There is research being done into how stratospheric aerosol injection would work. For one, we’d have to get our aerosol into the stratosphere, or about 11-20 km (6.8-12 miles) above sea level depending on latitude. At this elevation, atmospheric dynamics would keep the aerosols aloft and it’s too high for rain to form and wash aerosols out of the sky. Commercial airliners do cruise in the lowest layers of the stratosphere, so modified aircraft could be used to spray the aerosols into the upper atmosphere. Other delivery system proposals include high-altitude balloons and enormous artillery cannons, with the deciding factor likely being cost. Next, we need to decide on what aerosol to use. Volcanoes cause solar dimming primarily by emitting sulfur-containing compounds that break down into aerosols, so much of the current research looks at compounds like sulfur dioxide, sulfate, and sulfuric acid (more on this later). Other proposed compounds include calcite, aluminum oxide, titanium oxide, salt, or microscopic diamonds. Other areas of research include how best to aerosolize these compounds and the best locations to spray them. The current estimate is that it would take roughly five megatonnes of material sprayed into the stratosphere each year, or about the theoretical carrying capacity of twenty container ships, to return the Earth’s average temperature to pre-industrial levels. It would certainly be a feat of logistics to get this much material airbourne, but it would be within our ability with current technology. Delivering this much material to the stratosphere is predicted to require US$8 billion a year, comparable to the $8.7 per year cost to operate the New York City Subway system and far dwarfed by the roughly $140 billion per year cost of damages and lost productivity linked to climate change. If we stopped all CO2 emissions tomorrow, it would still not be enough to prevent warming of 1.2°C by the end of the century. With this technology, we could prevent even this warming, potentially saving millions of lives and improving the health of the planet.
The Controversy
So if stratospheric aerosol injection is such a magic bullet for defeating climate change, why are there countries that ban the practice? Why has research on the topic been slow in recent decades due to controversy? Why do many environmentalists adamantly oppose it? Well, there are some very notable drawbacks to SAI as well as other forms of radiation management. For one, it is an unproven technology with the potential to have harmful downstream effects of its own. Research conducted after the Mt. Pinatubo eruption found that on top of causing 0.5°C of temporary cooling, there was also a significant erosion of the ozone layer and a global uptick in acid rain. This could be prevented by choosing a different aerosol, but there is less research into other compounds. Volcanic eruptions are also known to cause regional changes in rainfall, potentially impacting agriculture and drinking water in affected regions. While the global effect of these changes would be far lesser than those of climate change, some regions might be more negatively affected than others. Further study is required to ensure it wouldn’t be worse than doing nothing, and over whom these studies are performed has already caused controversy. There’s also the risk of termination shock; if we were to ever stop spraying aerosols, the climate would return to its current state extremely quickly and wreak havoc. We’ve caused a mass extinction by warming the planet 1°C over the course of two centuries, imagine the devastation caused by this much warming in only a few years. Once we start geoengineering, we won’t be able to stop until we’ve lowered our production of CO2 and removed it from the atmosphere.
This all orbits around the biggest criticism of climate engineering in general and stratospheric aerosol injection in particular, the fact that it is a temporary short-term solution. We would have to reapply stratospheric aerosols regularly as they do fall out of the sky at a very slow rate. We can use aerosols to prevent the negative effects of our current carbon emissions, but in the long-term we need to stop emitting CO2 altogether. The concern critics of climate engineering have is that there is nothing more permanent than a temporary solution. That if we took away the destructive consequences of climate change, there would be nothing to motivate governments and corporations to transition to green energy. This wouldn’t just be lazy, but potentially very dangerous in the long-term. If we chose to continue burning fossil fuels and using SAI to prevent their side effects, we would have to inject more and more aerosols each year to account for the new CO2 emissions. Eventually, the aerosols we’d need to inject each year would eclipse our capacity to do so and the planet would begin to warm again. If this warming became destructive enough to prevent further SAI, the termination shock would be apocalyptic. Not to mention that our efforts to prevent climate change do have small-scale benefits to certain communities, such as habitat restoration improving land quality for marginalized communities such as indigenous groups. If we relied solely on SAI to prevent climate change, the benefits might not be as evenly distributed as those from cutting carbon emissions.
Every legitimate discussion of geoengineering considers it to be a stopgap while we decarbonize our energy grid. The process would need to be tightly regulated by a single entity, likely the UN or a similar international treaty group, in order to ensure we’re not injecting too much or too little. And every nation will need to remain committed to cutting their carbon emissions even if we begin geoengineering. But a quick look at the history of international policy on climate change shows why this is such a concern for critics of geoengineering. Numerous nations have deliberately misrepresented their carbon emissions in order to give the appearance they’ve met the goals set out by the Paris Climate Agreement (video from MinuteEarth for more details). And the Paris Climate Agreement was not legally binding, in large part because the United States refused to sign a binding resolution. Also remember the US left the Agreement during the Trump presidency. It’s reasonable to believe that our current political infrastructure is unsuitable for handling a project like SAI, where nations could continue to emit CO2 or back out of agreements without consequence. After all, if our political and economic systems were able to deal with long-term problems like this, we wouldn’t be dealing with climate change in the first place.
My Opinion
Everything I say after this point is my own viewpoint based on the most updated science.
Climate change is the biggest threat to our civilization at this time. To that end, just as I’ve said before with nuclear energy, I don’t believe we should be leaving any option off the table. We are not on target to prevent 1.5°C of warming as the Paris Agreement set out to do. To warm more than this puts millions of lives at risk. If this is a tool that can prevent these deaths, I believe we should be willing to use it. At the very least, we should be doing the research so we at least have it as an option. That said, the use of SAI needs to be married to incredibly strict regulation of CO2 emissions at the international level, with very real legal consequences for nations and institutions who don’t meet those standards, which I acknowledge will be an exceedingly hard sell in our current political climate. That said, I would argue we should be doing all that anyway. The fact that nations have been able to weasel out of the standards set by climate agreements in the past shows that we need to be better at enforcing these standards, regardless of whether or not we employ climate engineering. Perhaps having the conversation about stratospheric aerosol injection would create the impetus to push forward some of these much needed regulations. The problems of geoengineering are similar to the problems of climate change itself, namely unequal impacts on different people and regions and the moral hazards created when those with power aren’t the ones paying the price of their actions.
Fortunately, climate engineering and how to implement it is now being seriously considered. This is in large part due to how bad climate change is becoming and how important it has become for us to deal with the problem. Much research still needs to be done and how to perform this research in ways that are safe and fair to the people affected by it is still being considered. I do believe this will become a hot-button political issue in the near future, with the potential for both cautious consideration of contradicting needs and fracious line-drawing based on existing identities. But the ability to deliberately change our environment is a power we will soon have. Hopefully, we will use that power more responsibly than the powers that brought us here in the first place.
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