The theme for Earth Day 2020 is climate action. This may bring into mind environmental policy and implementation of sustainable practices such as the usage of renewable energy or water conservation in order to reduce the adverse effects of climate change. Geoengineering may also provide a solution. In this article, the two main branches and the economics of geoengineering will be discussed.
With the ever-increasing threat of climate change, governments must take more action to reduce its effects. Perhaps it would be beneficial to implement and enhance research in geoengineering, i.e. the deliberate manipulation of Earth’s environmental properties such as surface-albedo and ocean photosynthesis. Geoengineering branches out into two techniques: carbon dioxide removal and solar radiation management. These two divisions involve different aims and applications but share similarities in regards to their effects. Current studies mainly focus on modeling the effects of geoengineering practices on global temperatures, precipitation, etc. Aside from the science behind geoengineering, its economic practicality must be considered as well, as this will be a deciding factor on whether or not geoengineering is widely utilized.
A General Overview of Geoengineering
Geoengineering is the intentional large-scale alteration of Earth’s climate and environment through various techniques in order to mitigate the harmful impacts of anthropogenic climate change . It is widely controversial and many critics have raised questions on its ethics and economic risks. It has gained traction in recent decades.
The first use of the term “geoengineering” came with physicist Cesare Marchetti in the 1970s when describing a way in which the effects of fossil fuel combustion could be dealt with by the injection of carbon dioxide into the deep ocean. There is a second branch of geoengineering, however, which is known as solar radiation management .
Currently, most of the research taking place under the field of geoengineering is based on computer simulations to examine how geoengineering practices may affect global temperatures, the ozone layer, sea levels, and precipitation patterns . There are, however, some research groups that have or aim to conduct physical experiments on geoengineering.
Carbon Dioxide Removal
Human disruption of the biogeochemical carbon cycle is caused by processes such as fossil fuel combustion. For the first time in 2018, anthropogenic activities were responsible for 10 gigatonnes (also referred to as petagrams) of carbon emissions, nearly 37 gigatonnes of carbon dioxide . Around half of these emissions are absorbed by the biosphere and ocean, with the rest collecting in our atmosphere . These emissions can persist in the atmosphere for thousands of years. Through techniques that capture carbon dioxide from the atmosphere, it may be possible to reverse human CO2 emissions. One downside is that if implemented, carbon dioxide removal (CDR) would likely take substantial amounts of time. In fact, a computer modeling study conducted in 2010 by scientists Long Cao and Ken Caldeira at Stanford University found that in order to keep CO2 emissions at a specified level, a one-time reduction of excess atmospheric CO2 would have to be followed by long-term removal in order to achieve desired results . This is illustrated in the figure below. Furthermore, anthropogenic CO2 stored in the ocean and on land would have to be removed as well due to the fact that it outgasses to the atmosphere .
There are many approaches to removing carbon dioxide from the atmosphere, each with its own benefits and disadvantages . These methods include afforestation/reforestation, Biomass energy with CO2 sequestration (BECS), land-based weathering, ocean-based weathering, ocean fertilisation, and direct capture from air.
Afforestation and reforestation are two similar but distinct practices. Afforestation involves human-induced forest growth on land that has not been forested in the past. On the other hand, reforestation calls for the conversion of non-forested land to forested land in an area that had been forested previously . An ambitious afforestation and reforestation program has the prospect of decreasing atmospheric CO2 concentration by 40 to 70 ppm (parts per million) by the year 2100 . To put this into perspective, according to the National Oceanic and Atmospheric Administration, the global mean CO2 in January 2020 was 412.30 ppm .
Next, biomass energy with CO2 sequestration (BECS) essentially aims to capture CO2 from biomass-fueled electric power plants, subsequently storing it underground in a deep geological formation . The deep ocean could also be used as a carbon storage site. This technique would be repeatable and could result in net atmospheric CO2 removal as long as the biomass is not harvested in an unsustainable way, i.e., rapidly.
Two other techniques consist of land and ocean-based weathering . Weathering is defined as “the breaking down or dissolving of rocks and minerals on the surface of the Earth” . Natural chemical weathering reactions consume 0.1 Pg of carbon from atmospheric CO2 per year . Thus, it would take millennia for these processes to remove the amount of anthropogenic CO2 emitted in this century. The idea behind these processes is that the intentional acceleration of these chemical reactions could lead to a decrease in excess CO2. In this intentional acceleration, large quantities of silicate minerals would be mined, crushed and distributed on agricultural land with hopes that a portion of the atmospheric CO2 would be stored as a component of carbonate minerals or as bicarbonate ions in the ocean. Furthermore, would increase the pH level and carbonate mineral saturation of soils and ocean surface waters. With the increase of basicity, these silicate minerals may counteract the effects of ocean acidification. In ocean-based weathering, bases derived from silicate and carbonate rocks would be dissolved into the ocean, thereby increasing the ocean’s uptake of CO2.
Following this, there is ocean fertilisation . Photosynthesis in the ocean takes place through microorganisms known as phytoplankton. They are able to convert inorganic carbon compounds into organic ones. Some of this organic matter sinks into the deep ocean. In essence, phytoplankton takes CO2 from the atmosphere and converts it to an organic compound, which is transported to the deep ocean. A carbon dioxide removal strategy relating to this is adding nutrients into the ocean in order to increase planktonic productivity. The most discussed fertilizers have been iron, nitrogen, and phosphate, with iron being the most widely discussed. This method is not without its cons, however, as if not done carefully, ocean fertilisation can lead to eutrophication – excess nutrients in a body of water which can result in a harmful algae bloom .
Lastly, CDR via direct air capture (DAC) involves the extraction of CO2 from ambient air at any location on Earth . Location is not important to this method because CO2 in ambient air is distributed evenly across the globe. This technology allows a reduction of net CO2 emissions without a total transformation of our energy system. There are three methods used in DAC: adsorption on solids, absorption into highly alkaline solution, absorption into moderately alkaline solutions with a catalyst . A common technique includes large fans that move ambient air through a filter, using a chemical adsorbent (a usually solid material that causes a gas or liquid to form a thin film on its surface) to produce pure CO2, which can be stored . Leading companies currently working on DAC technology include Carbon Engineering in Canada, Global Thermostat in the US, and Climeworks in Switzerland . These will be further discussed in the section “Major Research Programs and Companies.”
Solar Radiation Management
The second major branch of geoengineering is Solar Radiation Management (SRM) – also known as solar geoengineering – which aims to reduce the amount of sunlight absorbed by Earth . The Earth absorbs approximately 240 W of sunlight per square meter. Doubling of atmospheric CO2 causes a radiative forcing (defined as the “change in Earth’s energy balance between incoming solar radiation energy and outgoing thermal IR emission energy” ) of approximately 4Wm−2 . In order to offset this, around 1.7% of incoming solar radiation must be reflected. A 2007 computer model study predicted that this reflection of incoming sunlight may produce a cooling effect on Earth within months . This may aid in preventing the many damaging effects of climate change. The study found that in a non-geoengineered simulation, global temperatures increased by 3.5°C from 1900 to 2100. Precipitation increased over the oceans and decreased on land. In contrast to this, in the fully geoengineered simulation, 2100 global temperatures were similar to that of 1900 and global average precipitation decreased by 0.18 mm per day from 1900 to 2100.
Furthermore, the researchers tested the influence of year of geoengineering implementation on achieving climate change countering effects. In the end, in all geoengineering simulations, global temperatures decreased to pre-industrial conditions in a time span of approximately 5 years.
Just as there are many methods in CDR, there are different techniques used in solar radiation management. These are categorised as space-based approaches, stratospheric aerosol-based approaches, marine cloud brightening, and surface-albedo enhancement .
Space-based approaches involve a sort of mirror or glass shield, placed in locations between the Earth and Sun, either in orbit around the Earth or a place in which the forces pulling the object towards the Sun are balanced with the forces pulling the object towards Earth. However, to offset the annual increase in radiative forcing due to human CO2 emissions, more than 10,000 km2 of reflective are would need to be deployed annually .
The stratospheric aerosol-based approach involves the insertion of sulfate aerosols into thelower stratosphere which would scatter solar radiation back into space and consequently produce a cooling effect . A natural version of this can be observed in large volcanic eruptions, such as the eruption of Mount Pinatubo in 1991. This eruption injected enough material into the atmosphere to offset approximately 4 W m−2 of radiative forcing which is the approximate needed amount to offset the global-mean radiative forcing from the doubling of atmospheric CO2. It must be noted that volcanic eruptions do not perfectly imitate geoengineering conditions, but rather, produce similar effects. Also, the aerosols injected into the atmosphere by Mount Pinatubo were removed from the atmosphere in around a year. Had these aerosols stayed in the atmosphere for longer, further cooling would have been observed, in comparison to the approximately 0.5 Kelvin cooling within the year after the eruption. A multitude of techniques have been proposed in order to inject sulfate aerosols into the atmosphere, including high-altitude balloons, artillery guns, high-level aircraft, tall towers, and space elevators, with the last one being currently unfeasible. This method has many disadvantages such as the fact that sulfate aerosols can influence the chemical properties of the stratosphere, specifically ozone concentration. In fact, the injection of sulfate aerosols may provide surfacing leading to efficient chlorine activation, doubling the ozone-destroying potential of chlorofluorocarbon-derived chlorine in the poles. This means that the Antarctic ozone hole would take longer to recover.
Marine cloud brightening works by increasing the quantity of cloud condensation nuclei (CCN) – “particles on which water condenses at supersaturations typical of atmospheric cloud formation”  – which would subsequently increase the reflectivity of low-level marine stratocumulus clouds . More CCN increase the number of cloud droplets but decrease their size. When cloud droplet quantity is increased, total droplet surface area increases as well, which means higher reflectivity. This is merely a prediction, though, as it is not certain that reduced droplet size would mean an increase in albedo.
Finally, there is an approach known as surface-albedo enhancement . Various methods have been proposed regarding this approach: modifying the reflectivities of rural areas, urban areas, deserts, and the ocean surface. One outright disadvantage of the application of technique on land is that approximately 10% of solar radiation on the global land surface would need to be reflected to offset the radiative forcing from a doubling of atmospheric CO2. This stems from the fact that land represents less than one-third of the Earth’s surface, with half of that land being covered by clouds. Some ideas of surface-albedo enhancement involve increasing crop albedo (by increasing crop brightness) and installing white roofs on a global scale.
Economics of Geoengineering
Most likely the greatest issue with implementing methods of geoengineering – other than some environmental risks attributed to certain approaches – is cost. Costs for various solar radiation management and carbon dioxide removal techniques range widely. For instance, when considering SRM, space mirrors are highly expensive, whereas stratospheric aerosol albedo modification is not . This is because the modification of stratospheric aerosol would not require significant advancements in current technology.
A 2009 study by Robock et al. found that injection of 1 teragram (1 Mt or 1,000,000,000 kilograms) of sulfur gas per year would cost $4,175,000,000 annually using an F-15C Eagle, $375,000,000 using a KC-135 Tanker, $225,000,000 using a $375,000,000 KC-10 Extender, $30,000,000,000 using naval rifles, and $21,000,000,000– $30,000,000,000 using stratospheric ballons (all of these values are according to 2008 USD) . The F-15C Eagle, KC-135 Tanker, and KC-10 Extender are US military planes.
Another stratospheric aerosol albedo modification study by McClellan et al. examined costs (based on USD for the 2010 fiscal year) for approaches such as Boeing 747 Class airplanes, hybrid airships, and floating gas pipes, while also taking into account the altitude each technique would be used in . All costs were calculated in terms of 1 Mt (1,000,000,000 kg) of material per year. These results are shown in Figure 4. As demonstrated by these two studies, aircraft usage is estimated to be the cheapest option for stratospheric aerosol albedo modification.
In the case of CDR, a 2011 comprehensive report by the American Physical Society (APS) claimed that Direct Air Capture (DAC) would cost an estimated $600 per tonne of CO2 . Climeworks, a company based in Switzerland, confirm this estimation, stating that capturing a tonne of CO2 at their plant costs around $600 . In contrast to this, some companies such as Carbon Engineering in Canada assert that the price would be much lower. In June 2018, researchers at the company, including David W. Keith – Harvard applied physics professor and acting chief scientist at Carbon Engineering – published a paper on the costs of DAC. They found that costs range from $94 to $232 per tonne of captured atmospheric CO2 . Both the APS and the Carbon Engineering study included a plant that captures 1 Mt of CO2 per year.
Climate change is rapidly worsening, leading to damaging environmental effects. It has become clear that new policies or strategies must be implemented to reduce these effects, such as shifting from fossil fuels to renewable energy, however, many countries are not. As a result, it may become necessary to utilize innovative technologies to combat climate change. Geoengineering, although widely controversial, may be one of these.
Geoengineering consists of carbon dioxide removal (CDR) and solar radiation management (SRM). CDR has many approaches; some, such as re- or afforestation, can be considered more natural, while others, such as ocean fertilisation, involve synthetic manipulation of the environment. SRM is concerned with increasing the reflectivity of Earth in order to decrease absorbed solar radiation.
Numerous studies have examined the potential price of CDR and SRM. Results vary widely but most estimate that geoengineering practices would cost millions, if not billions, of dollars. Some practices may be more economically viable than others. In the end, it is important to remember that the future of planet Earth relies on adjusting either policy or the planet itself.
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Fig. 1: Cao, Long, and Ken Caldeira. 2010. “Atmospheric Carbon Dioxide Removal: Long-Term Consequences And Commitment”. Iopscience.Iop.Org. https://iopscience.iop.org/article/10.1088/1748-9326/5/2/024011/meta.
Fig. 2: Matthews, H. Damon, and Ken Caldeira. 2007. “Transient Climate–Carbon Simulations Of Planetary Geoengineering”. https://www.pnas.org/content/104/24/9949.
Fig. 3: Matthews, H. Damon, and Ken Caldeira. 2007. “Transient Climate–Carbon Simulations Of Planetary Geoengineering”. https://www.pnas.org/content/104/24/9949.
Fig. 4: McClellan, Justin, David W. Keith, and Jay Apt. 2012. “Cost Analysis Of Stratospheric Albedo Modification Delivery Systems”. Institute Of Physics. https://iopscience.iop.org/article/10.1088/1748-9326/7/3/034019.