Can we geoengineer our way out of climate change?

 We are facing an unprecedented threat to our planet. What are some solutions?

Climate Change and Global Warming

We see the results of climate change every day, including global warming, sea-level rise, acidification of the oceans (1), and heatwaves (2). Periods of global warming and cooling, together called climate change, have happened naturally many times during Earth’s history (Figure 1). The natural fluctuations in Figure 1 are called Milankovitch cycles and are caused by variations in the planet’s tilt, orbit, and rotation; these changes determine how much sunlight reaches the Earth (3). When more sunlight reaches the Earth’s surface, a major effect is the warming of the oceans. This lowers the solubility of the vast amount of carbon dioxide (CO₂) dissolved in the ocean and leads to its release into the atmosphere (1). CO₂ is a greenhouse gas, which means that an increase in atmospheric CO₂ causes more heat to be trapped in Earth’s atmosphere (4).

The current bout of global warming differs from past natural warming events. Figure 1 shows that today’s warming episode is more rapid, coinciding with an increase of atmospheric CO₂ from 314 parts per million (ppm) in the 1950s to about 414 ppm now (5). The increase in CO₂ is caused mostly by human activities that involve the burning of fossil fuels, which release CO₂ when burned. Fossil fuels power factories and vehicles and supply much of the energy we need to heat our homes and supply our electricity (6).For years, international organizations, governments, scientists, and individuals have been trying to find ways to reverse or slow global warming by reducing CO₂ emissions. Geoengineering seeks to go further and directly address global warming by either reducing the concentration of CO₂ in the atmosphere or by changing the amount of solar radiation reaching the Earth’s surface (7). This article discusses the pros and cons of three types of geoengineering. The first type harnesses the chemistry of the oceans to remove CO₂ from the atmosphere. The second reflects light to space from sea ice. The third solution condenses CO₂ and stores it in the ground in a process called sequestration.

Iron Fertilization: Changing Ocean Chemistry

         One geoengineering approach for removing CO₂ from the atmosphere is changing the chemistry of the ocean by adding iron sulfate. This process of iron fertilization has been tested in many locations, such as the northern part of the Pacific Ocean (8) and in the South Pacific and South Atlantic Oceans (9). Soluble iron increases the growth of plankton, which are microscopic photosynthetic creatures that live near the ocean’s surface. This increased growth enhances the amount of CO₂ removed from the atmosphere (10). 

         There are many advantages of iron fertilization as a method for removing CO₂ from the atmosphere. Iron fertilization would be relatively inexpensive, and its effectiveness has been proved. Preliminary experiments show that one atom of iron would lead to enough plankton growth to remove 10,000 to 100,000 molecules of CO₂ from the atmosphere (11). Removal of such a large number of CO₂ molecules would enable this process to be extremely effective. 

         Some drawbacks to iron fertilization are possible overstimulation of phytoplankton growth, leading to an unbalanced ecosystem (9). Live plankton also produce gases that can erode the layer of protective ozone in the upper atmosphere (12). Dead plankton can increase the nitrous oxide and methane levels in the atmosphere when they decompose on the seafloor (12). Although this process would not completely negate the benefits of iron fertilization, methane and nitrous oxide are themselves greenhouse gases.

Glass on Arctic Sea Ice

Geoengineering has also been tested as a method to preserve Arctic Ocean sea ice. Ice formed from sea water in the Arctic Ocean is vital for keeping Earth cool. When sunlight hits the ice, it returns 80% of this light to space. Without the ice, 90% of this sunlight is absorbed into the ocean, a process that contributes to further warming of the oceans and ultimately Earth’s climate (13).

As shown in Figure 3, the area of annual arctic sea ice has decreased by 43% or by more than 3 million square kilometers of sea ice (about one-third the area of the United States) since the 1980s. Scientists that founded the Arctic Ice Project developed a geoengineering approach to reverse the rapid decline of sea ice by spreading 65 micron natural silica (glass) beads on the surface of ice floes. The beads, which are hollow and too large to be inhaled by animals, reflect sunlight while protecting the ice and allowing it to grow thicker. The beads can also be spread on the ocean surface, where they reflect sunlight as sea ice would. This geoengineering solution is achievable and environmentally-friendly (14). 

However, the approach is expensive, costing an estimated $1 to $5 billion annually to disseminate the beads in the Fram Strait, which is a small part of the Arctic Ocean. Ocean currents may cause rapid dispersion of the beads, which would reduce their effectiveness. In addition, zooplankton called copepods, which are at the bottom of the food chain, consume particles of the same size as the beads. If the copepods eat the beads instead of actual food, they would starve and more advanced organisms that depend on them for food would also be affected (14).

Carbon Sequestration

         One of the most commonly discussed geoengineering approaches is carbon sequestration, which can be either biologic or geologic. Sequestration refers to keeping CO₂ out of the atmosphere by trapping it. Biologic sequestration involves increasing the biomass of organisms (such as plants and phytoplankton) that use or absorb CO₂. Geologic sequestration involves capturing CO₂ as it is being emitted to the atmosphere, condensing it into a liquid, and injecting this liquid into rock far below Earth’s surface (15) or on or under the seafloor. Depending on where the CO₂ is injected, it may remain as a liquid, combine with water to form a type of CO₂ ice, or react with basalt and solidify into rock (16).

         Carbon sequestration occurs naturally, and the geoengineered concept of carbon sequestration has been proved in demonstration projects. The process can keep CO₂ out of the atmosphere for millions of years (17). The U.S. government has assessed and identified land areas that would be appropriate for geologic sequestration (18), and the U.S. and others have completed preliminary tests.

         Geologic carbon sequestration has many advantages, but there are a few challenges as well. Diverting CO₂ from smokestacks is already possible, but expensive, and significant energy must be used to prepare CO₂ for sequestration, often leading to the use of more fossil fuels (19). CO₂ might also be extracted directly from the atmosphere. A company called Climeworks has developed technology to filter up to 90% of CO₂ from the air (17). However, the applicability of this technology on a global scale is unknown. In addition, finding and preparing sufficient locations for geologic sequestration will require time and a significant financial commitment.  

Is Geoengineering the Solution?

The examples here are only three of the many types of geoengineering that are being evaluated. The United Nations has said that “inevitably” some method of atmospheric greenhouse gas removal (or other type of geoengineering) will be required to address global warming (20). However, all available types of geoengineering have disadvantages in terms of cost, energy consumption, or logistics.Opponents of geoengineering are concerned about making changes to Earth’s complex systems and producing unforeseen consequences. Geoengineering is not currently regulated, and implementation of a geoengineering solution by one country may have a negative impact on another area. In lieu of geoengineering, opponents offer working towards zero emissions of CO₂. However, the goal of zero emissions may not be reached fast enough to reverse global warming (7), meaning that geoengineering will likely be one of the tools needed to address climate change in the 21st century.

– Amelia How

References

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Images

1. https://www.ncdc.noaa.gov/sites/default/files/Temperature-change-and-carbon-dioxide-change-measured-from-the-EPICA-Dome-C-ice-core-in-Antarctica-v2.jpg
2. https://lh4.googleusercontent.com/KLvIaHVL7cp4KY4H5Nw6IyvCDa7K1JHio5OVmuVvXij1ysZ5QhxvRASMMFHFuulX0WFn6xQNXAr3r94cXHBuVfzV8zXZFxwe9egXGqJttqdyN9bbjX6GaSBd78czlLuJZfzZdotR
3. https://climate.nasa.gov/vital-signs/arctic-sea-ice/