Removal or Failure of Climate Engineering by Sulfate Aerosol Injection Poses Dangerously Abrupt Temperature Increases

Sulfate aerosol injection as a method of geoengineering and cooling the planet has been showing great promise and growing in popularity in regards to fixing the climate crisis. It has long been suggested that geoengineering could function independently and provide researchers with more time to improve and create methods of removing CO2 from the atmosphere, which is the real fix. Ross et al. (2009), however, claim that if we rely on geoengineering and do not implement it alongside the removal of CO2, there will be drastic temperature changes if the geoengineering strategy is removed or fails. If CO2 emissions do not decrease, the failure or removal of climate engineering methods would result in a large temperature spike, increasing global temperatures by a maximum of 4.5 °C, which would have catastrophic impacts on the planet’s ecosystems and possibly result in mass species extinctions.— Ellie Pickrell
Ross, A., Matthews, H., 2009. Climate engineering and the risk of rapid climate change. Environmental Resolution Letters 4, 045103.

 In this study, Ross et al. used a climate model to predict the effects of the implementation and subsequent removal of climate engineering by injection of sulfate aerosols with the A1B emissions scenario. The control group consisted of a business as usual emissions scenario. The second simulation consisted of a model exposed to climate engineering that started in the year 2020 and was removed in 2060. These two simulations were repeated 40 times each, varying with climate sensitivity of the model from 0.5 to 10 ° C. Climate sensitivity is the response of global mean surface air temperature to a doubling of atmospheric CO2 concentrations. An estimated climate sensitivity probability density function was used from another paper (Hegerl et al. 2006) to identify the likelihood of each set of model situations.
In the control group where climate engineering was not applied, temperatures increased consistently from 1990 to 2100, ranging from 0.6 to 5.1 °C for climate sensitivities ranging from 0.5 to 10 °C.  Atmospheric CO2 concentrations at the year 2100 ranged from 690 to 739 ppmv, with higher climate sensitivities containing the higher concentrations. In the climate engineered simulations, temperatures dropped to values very similar to the temperatures in 1990 between 2020 and 2059, with respect to the control scenario. As soon as the engineering was removed, however, temperatures increased rapidly, ranging from 0.15 to 4.5 °C between 2060 and 2100. The temperature change after the removal of the engineering was higher with higher values of climate sensitivity. The final CO2 concentrations in the geoengineering runs were similar to those in the control simulations (between 689 and 722 ppmv).
Next, Ross et al. looked at the annual rate of temperature change between 1990 and 2100 for each simulation. In the control scenario, the annual rate of temperature change increased until 2060, whens greenhouse gas emissions decline with the A1B emissions scenario. This resulted in a decreased rate of temperature change. In the climate engineering scenarios, the rate of temperature change was relatively small up until 2020, when geoeningeering was implemented and temperatures dropped. From 2020 to 2060 the rate of temperature change was insignificant, until temperatures abruptly increased after the removal of geoengineering. The maximum rate of warming ranged from 0.13 to 0.76 °C/year. These high rates of warming, however, only lasted for a few years and within a decade, the rates decreased to less than 0.1 °C/year. The maximum rate of sea level rise was also higher in the geoengineering simulations than in the controls.
Finally, Ross et al. looked at the probability density functions between 1990 and 2100, which measures the likelihood that these temperatures will change. For the control group, the most likely maximum annual temperate change was 0.031°/year. The geoengineering simulation showed a likely maximum rate of temperature change just under 0.5 °C/year, which occurred in 2060 at the high temperature spike. 

Positive Effects of Geoengineering on Ocean Acidification and Aragonite Saturation Levels

In the past geoengineering has been considered as a promising strategy for global cooling, although it has had some drawbacks. One of these drawbacks was the common belief that engineering the climate would not have any beneficial effects on ocean acidification, which is a negative component of climate change. The writers of this paper, however, proposed that geoengineering could have a beneficial impact on ocean acidification and offset some of the impacts that greenhouse gas emissions have had on our planet’s oceans, specifically pH levels. Aquatic organisms that rely on shells for survival can only build these shells in waters with higher aragonite saturation values, and as the ocean becomes more acidic, the aragonite saturation levels go down, and these organisms cannot survive. Climate engineering could potentially slow the ocean’s current pH decreases, which would ideally slow the rapid reduction of aragonite saturation in the oceans (Matthews et al, 2009). But, although simulations from this experiment do show an increase in oceanic pH values, but not a significant enough increase to stop the rapid decline in aragonite saturation levels. — Ellie Pickrell
Matthews, H., Cao, L., Caldeira, K., 2009. Sensitivity of ocean acidification to geoengineered climate stabilization. Geophysical Research Letters, 36.

 Matthews et al. conducted a series of experiments on an earth system model that resembled a world exposed to climate engineering. They performed five simulations which all began at a preindustrial climate equilibrium, and compared the model’s results at what represented conditions in the year 2100. The control group, A2, lacked climate engineering and consisted of prescribed SRES CO2 emissions. The next simulation, A2+eng consisted of prescribed CO2 emissions and climate engineering, which began after 2010. Next was the A2A+ eng, which consisted of the same CO2 emissions as simulation A2, but again was exposed to climate engineering after 2010. The first three simulations were representing a world with an active biosphere, which means that the land biosphere was exchanging carbon with the atmosphere, i.e. carbon sinks. The fourth simulation, A2nb, consisted of a neutral biosphere (the land biosphere does not exchange carbon with the atmosphere after 2010), prescribed CO2 emissions, and no geoengineering. The final simulation, A2nb+eng was the same as the previous simulation, but was exposed to climate engineering.
     After all of the simulations were tested, Matthews et al. compared the results of the pH and the aragonite tests between the different scenarios. In both the A2 and A2+ eng simulations, pH values were reduced (7.6 and 7.85), compared to the control group with a pH value of 8.05, and aragonite concentrations of 1.85. A model with climate engineering showed a slightly higher pH value at the 2100 mark in comparison to the A2 non-engineered simulation, but a lower aragonite saturation value (1.80 to 1.90). Climate engineering was also effective at reducing the average atmospheric temperatures, as well as lower atmospheric CO2 concentrations, due to an increase in carbon uptake by natural carbon sinks as a result of the cooler temperatures.
     In the A2A+eng simulation, the change in ocean pH was smaller and was extremely close to the control simulation’s pH, but the aragonite saturation decreased more rapidly as a result of climate engineering. An increase in dissolved inorganic carbon and colder temperatures lead to aragonite saturation values that were 9% lower than the values in the A2 simulation (from 1.72 in A2 to 1.58 in A2A+eng), because colder temperatures lead to slightly higher pH values, but result in lower aragonite saturation values.
     Next, A2nb+eng and A2nb were compared. In A2nb+eng, surface temperatures were colder, and ocean dissolved inorganic carbon values were higher than in A2nb, which created unaffected pH values and a further decrease in aragonite saturation relative to the non-engineered simulation. The A2nb+eng simulation had a pH value of 7.75, and aragonite saturation values of 1.7, while the A2nb simulation had a pH value of 7.25 and aragonite saturation values of 1.85.
     These effects and results are dependent on the enhanced accumulation of carbon in the land biosphere. Without this accumulation of carbon, climate engineering will have little effect on ocean pH levels, which would then lead to accelerated declines in aragonite saturation. 

Although Sulfate Aerosol Injections May Cool the Planet They Still Reduce the Amount of Ozone in the Earth’s Atmosphere

Geoengineering is a climate manipulating strategy that could potentially cool the planet and give researchers more time to find an efficient way to remove CO2 from the atmosphere. Injecting sulfate aerosol particles into the Earth’s atmosphere is one of the most popular strategies of geoengineering, as it would increase the albedo of the planet and reflect more light back into space. These sulfate aerosols, however, have to be a certain size to be effective in increasing the planet’s albedo, and particles with a radii of roughly 0.1 mm are the most efficient in cooling the planet (Heckendorn, et al, 2009). This paper shows which injection strategies will produce the smallest and most efficient aerosol particles, and how long these particles will stay in the atmosphere. This is of large concern since there is great speculation regarding aerosol injection, and if it ends up having negative impacts it would be even worse if the particles remained in the atmosphere for long periods of time. This paper also explains how risky injecting sulfate aerosols into the atmosphere can be, as increase aerosols reduce the amount of ozone in the atmosphere. Ellie Pickrell
Heckendorn, P., Weisenstein, D., Fueglistaler, S., Luo, B., Rozanov, E., Schraner, M., Thomason, L., Peter, T., 2009. The impact of geoengineering aerosols on stratospheric temperature and ozone. Environmental Resolution Letters 4.

     Heckendorn et al ran a series of experiments on a global model. These calculations were carried out with two types of sulfur injection methods. The first was a continuous pumping of sulfur into the clouds with fluxes of 1,2,5 and 10 Mt/a, while the other simulations were pulsed injections with periods of one month and six months with fluxes of 5 Mt/a. The control group consisted of zero sulfur injections. All simulations were run for twenty-years with present day concentrations of ozone depleting substances, green house gas, carbon dioxide emissions, sea ice and sea surface temperatures.
     The results of the simulations show that the surface area density of the aerosol particles increases as concentration increases.  In simulation GEO5 (continuous injection with fluxes of 5 MT/a) the surface area density is larger than 40 mm2 cm-3. In the simulation where the injection takes place twice a year (GEO5p2), the surface area density is larger than 100 mm2 cm-3.
     Next, Heckendorn et al looked at how the injection strategies affected the stratospheric residence time of the aerosols. They found that smaller particles have a longer residence time. For the GEO1 simulation (continuous injection with fluxes of 1 Mt/a), the residence time, referred to as aerosol burden, is 1.4 Mt S. For all the other simulations, the aerosol burden is less than one year with 3.7 Mt S for the GEO5 simulation and 6.0 Mt S for the GEO10 simulation (continuous injections with fluxes of 10 Mt/a). They also found that if the sulfur injection occurs at a higher altitude, the residence time increases.
     Finally, Heckendorn et al looked at how the injection strategies would affect the mean O3 column. For the GEO5 simulation, the O3 column is predicted to decrease by 4.5%, and the GEO10 model predicted a decrease by 5.3%. These values are greater than the O3 loss due to the emission of greenhouse gases from 2002 to 2005, a decrease by 3.5%.
     Although geoengineering by injection of sulfur aerosols into the Earth’s clouds has shown promise in cooling the planet and decrease levels of atmospheric CO2 concentrations, it also has the negative impact of reducing the Earth’s ozone layer. 

Solar Radiation Management Geoengineering: Possible Solution for the Shrinking Greenland Ice Sheet

The effects that climate change has on polar ice sheets, particularly Greenland in this study, are important for many reasons. The two most important reasons that are discussed in this article involve rising sea levels and decreased planetary albedo as the globe’s ice sheets melt. Solar radiation management has been suggested to reduce the warming of the globe and buy some time while engineers and scientists address the larger problem of removing CO2 from the atmosphere. The installation of a solar “sunshade” or the injection of sulfate aerosols into the clouds are the two most promising methods of geoengineering. Previous studies have shown that a world exposed to climate engineering would experience warming at the poles, cooling in the tropics, and a decreased precipitation rate, which may have certain effects on the Greenland ice sheet (Irvine et al.). In this study, the melting of the Greenland ice sheet was prevented at levels of partial climate manipulation, which suggests that the geoengineering required to cool the planet and reduce the impacts of greenhouse warming may not be as thorough as geoengineers originally believed. Ellie Pickrell
Irvine, Peter J., Lunt, Daniel J., Stone, Emma J., Ridgwell, Andy, 2009. The Fate of the Greenland Ice Sheet in a Geoengineered, High CO2 World. Environmental Research Letters, 4.

Irvine et al. conducted twelve 400-year simulations on a climate model. The first model was control simulation that modeled a climate similar to that of a pre-industrial world, and wasn’t exposed to climate engineering. The second has atmospheric CO2 concentrations of 1120 ppmv, which is four times the pre-industrial amount, and 0% climate manipulation. The last ten simulations have the same CO2 concentrations and range from 10% to 100% climate engineering by intervals of 10%. At each simulation, Irvine et al. measured the temperature and precipitation anomalies in comparison to the control simulation. The results were then combined with an observed climatology to create an ice-sheet model—Glimmer. Glimmer is a three-dimensional ice sheet model representing the Greenland region, and provided results showing the impact of solar radiation management on the ice sheet.
In the simulation with 0% climate engineering, the center of the Greenland ice sheet had an annual temperature increase of 8°C, and an average summer temperature that increased by 6°C when compared to the pre-industrial simulation. This 0% geoengineering simulation also showed an increase in annual precipitation of over 6 meters a year, which would increase the amount of annual snowfall, which could potentially cause the ice sheet to grow.
For simulations experiencing 100% engineering, the annual average surface air temperature was significantly lower than simulations with lower climate manipulation, although Greenland remained warmer than it was in the pre-industrial period. The island showed an increase of at least 0.5°C, with its northern and southern coasts undergoing an increase of 0.75°C, and a 1°C increase at the southern tip. For simulations experiencing 50% engineering, the model predicted a warming of 3°C across the majority of Greenland. Both 100% and 50% simulations showed an increase in precipitation rates, although it was lower than the 0% engineering simulation. A 100% simulation resulted in a precipitation rate of 21 mm per year.
The results from the Glimmer test were then used to predict the change in sea level of the Greenland region. In the pre-industrial control simulation, the sea levels were at 8.6 m. In the 0% simulation, only 12.8% of the original ice sheet remained, which could result in a sea level rise of 6.4 m.  The remaining 12.8% of the ice sheet is located at the high altitude regions on the southern tip and on the eastern coastline. In the 100% simulation, there was a sea level increase of 0.1 cm. These results show that as the climate engineering percentage came closer to 100%, the volume of the ice sheet increased.
The Glimmer test also showed that there was no linear relationship, rather a step-like behavior, between an increase in climate engineering and an increase in height and coverage of the ice sheet. The 20% simulation showed an ice sheet that was slightly larger than the 0% simulation, but the remaining ice sheet was more inter-connected. The 30% and 40% simulations show slight increases from the previous simulation, with a partial ice sheet in the north that wasn’t present in the 20% simulation. The ice sheet at the 60% simulation was at full height and coverage, and the pre-industrial ice sheet was maintained.
For all of the simulations that include geoengineering, Greenland experiences a warmer and wetter climate in comparison to the pre-industrial period. On average, the temperature and precipitation rates of Greenland decrease relatively linearly with increases in the level of climate manipulation.

Cloud Seeding: A Promising Strategy for Cooling the Planet and Rebuilding the Polar Ice Caps

Cloud seeding has been seen as a possible method of decreasing the overall surface temperature of the globe. Seeding our planets maritime boundary layer clouds would increase the number of raindrops released from these clouds and reduce the average droplet size, thus increasing their albedo (Rasch et al. 2009). This could result in the cooling of the planet and compensation for some of the negative effects of climate change. The effects of cloud seeding were looked at on a model that represented a globe whose atmospheric CO2 concentrations were twice as high as they are today. Global surface temperature, polar sea ice cover, and the global precipitation rate would experience drastic changes if this cloud seeding strategy were put into action. We would see an overall cooling of the planet, a halt in the rapid shrinking of the polar ice caps, and an overall decrease in the global rate of precipitation.—Ellie Pickrell
 Rasch, Philip J., Latham, John, Chen, Jack, 2009. Geoengineering by Cloud Seeding: Influence on Sea Ice and Climate System. Environmental Research Letters, 4.
     Philip J. Rasch and the Pacific Northwest National Laboratory conducted an experiment where they examined the effects of cloud seeding on an “Earth” with atmospheric CO2 concentrations that were twice as high as present day values. They used a Community Climate System Model and set up four different geoengineering situations, with a control system that consisted of zero climate engineering. The four cases were 20%, 30%, 40%, and 70% cloud seeding of the areal extent of the ocean surface. They then examined the effects that these four situations had on global surface temperature, polar sea ice, and global precipitation.
     The test showing effects of cloud seeding on the Earth’s surface temperature produced promising results. The control group showed an increased surface temperature by 1.8 K compared to the Earth’s current conditions, but the models that included cloud seeding show much more positive results. In the 20% case, the warming is reduced to 0.8 K more than the current day temperatures, which is almost half as much heating if we were to dismiss the idea of cloud seeding. The 70% case actually produced a cooling of 0.4 K less than the current day temperatures, which would actually result in an overcooling of the planet. Based on the results, it is clear that the maximum amount of cloud seeding isn’t necessary, and even the minimum amount of 20% would make a fifty percent difference in the surface temperature.
     Next, they compared the results regarding the polar sea ice covers and their reaction to cloud seeding. In this experiment they looked at the effects that cloud seeding would have on the Northern Hemisphere and the Southern Hemisphere separately, as the clouds in the Southern Hemisphere require less seeding than the clouds in the Northern Hemisphere (they are more susceptible to brightening). The control group shows a 20% decrease in the Northern Hemisphere and a 36% decrease in the Southern Hemisphere from the current sea ice levels. In the 40% case the sea ice is 9% smaller than the control group in the Northern Hemisphere, and 8% smaller in the Southern Hemisphere. To really make a difference in the polar ice caps, the Earth requires a 70% cloud seeding strategy, which is almost impossible as it may overcool the Earth. Regardless, in the 70% case the sea ice is restored to within 2% of the present day level.
     Finally, they looked at the effect that cloud seeding could have on the global precipitation rate. As the percentage of cloud seeding increases, the global precipitation rate decreases. The control group shows an increase by 0.1 mm of rain, compared to the current day precipitation rate, per day. The 20% case shows an increase by 0.01 mm of rain, while the 70% case shows a decrease by 0.08 mm of rain. These reductions in precipitation occur along the equator between the eastern Pacific and the maritime subcontinent, especially across South America. For all the cases there is, however, an increase in precipitation in the South Pacific convergence zone.
     It is important to realize that this study shows how difficult it is to address multiple changes resulting from climate change. If the atmospheric CO2 concentrations were to double, it would be impossible to simultaneously cool the planet, or return sea ice and global precipitation to the present day amounts. —Ellie Pickrell