What Is Geoengineering, and How Does It Impact Climate Change?

Geoengineering, also known as climate engineering or climate intervention, broadly refers to the intentional, large-scale manipulation of Earth's natural climate processes. Applications of geoengineering are usually described in relation to how they could help offset the impacts of climate change.

As the Earth nears 2 degrees C of warming, an amount the International Panel on Climate Change (IPCC) aims to stay below, policymakers and scientists alike are seriously considering the use of geoengineering. The world is currently projected to exceed this temperature threshold based on current emissions rates. Although geoengineering technologies have yet to be scaled to levels great enough to affect Earth's climate, the potential of these strategies to combat — or even reverse — the effects of climate change has gained attention in recent years.

Types of Geoengineering

There are two primary types of geoengineering: solar geoengineering and carbon dioxide geoengineering. Solar geoengineering would manipulate the radiation the Earth receives from the sun, while carbon dioxide geoengineering would remove carbon dioxide from the atmosphere.

Solar Geoengineering

Solar geoengineering, or radiative forcing geoengineering, refers to methods of cooling the planet by altering the rate at which the Earth collects radiation from the sun. The Earth receives a relatively consistent amount of radiation from the sun. While this solar radiation is not considered to be a cause of climate change, reducing the amount of solar radiation the Earth receives could lower global temperatures, one of the main effects of climate change. Certain predictive models indicate solar geoengineering could return global temperatures to pre-industrial levels.

While solar geoengineering is expected to reduce global temperatures, it would not reduce the amount of greenhouse gases in Earth's atmosphere. Climate change effects that are not directly tied to warming temperatures, like ocean acidification, would not be reduced by solar geoengineering.

Carbon Dioxide Geoengineering

Carbon dioxide geoengineering refers to the manipulation of the planet to reduce the amount of carbon dioxide in the atmosphere. Unlike solar geoengineering, carbon dioxide engineering would target the root of the climate change problem by reducing atmospheric greenhouse gases directly.

In general, carbon dioxide geoengineering techniques leverage natural biological processes to pull carbon dioxide out of the atmosphere and store it. Carbon geoengineering would enhance these natural processes to fast-track the removal of carbon dioxide from the atmosphere.

How Exactly Is Geoengineering Conducted?

When it comes to solar geoengineering, scientists suggest manipulating the radiation the Earth receives by adding mirrors to space, injecting materials into the Earth's atmosphere, or increasing the reflectivity of Earth's land. The primary methods proposed for carbon dioxide geoengineering include fertilizing the ocean with iron, increasing forest surfaces on Earth, and implementing radiation reflection techniques.

Mirrors in Space

Walter Seifritz first suggested reflecting the sun's solar radiation through the addition of mirrors to space 1989. The concept was elaborated upon in a publication by James Early just three months later. A more recent 2006 estimate proposes the installation of a "cloud" of small sunshades in the Lagrange orbit, the location between the sun and the Earth where their respective gravitational pulls cancel each other out. In this location, mirrors would receive, and therefore reflect, solar radiation constantly. The study's author, Roger Angel, estimated the mirrors would cost a few trillion dollars.

Atmospheric Radiation Reflection

Others have suggested creating a mirror-effect in the Earth's atmosphere as a means of solar geoengineering. When fine particles, or aerosols, are suspended in the air, they similarly reflect solar radiation back towards space, preventing the solar radiation from coming through the atmosphere. By deliberately adding aerosols to the Earth's atmosphere, scientists could enhance this natural process.

The atmosphere could also be made more reflective by spraying clouds with droplets of seawater. The seawater would make the clouds whiter and more reflective.

Land-Based Solar Radiation Reflection

Scientists have also suggested a variety of ways to reduce the solar radiation Earth receives by adding sources of reflectivity on Earth's surface. Some land-based reflection ideas include using reflective materials on building roofs, installing reflectors in subtropical countries, or genetically modifying flora to produce lighter-colored species. To be most effective, these land-based reflectors would need to be in places that receive substantial sunlight.

Fertilizing the Ocean

One of the most discussed methods of carbon dioxide geoengineering is through the ocean's algae. Algae, or microscopic seaweeds, convert atmospheric carbon dioxide into oxygen and sugars through photosynthesis. In about 30% of the ocean, algae exist in low numbers due to a lack of an essential nutrient: iron. The sudden addition of iron can trigger a massive algae bloom. While these blooms do not normally produce dangerous byproducts like the harmful algal blooms that can wreak havoc on coastal waters, they can become just as large, with some growing to over 35,000 square miles.

Iron deliveries occur naturally, but relatively infrequently, through the upwelling of nutrients in the deep ocean to the surface, through wind carrying iron-rich dust, or by other more complicated means. When an algal bloom inevitably runs out of nutrients once again, most of the carbon stored in dead algae cells sinks to the ocean floor where it can remain stored. By fertilizing iron-deficient portions of the ocean with iron sulfate, scientists can induce these massive algae blooms to convert atmospheric carbon into carbon stored in the deep ocean.

Adding Forests

Similarly, by increasing the amount of the planet covered by forests, we could enhance the amount of photosynthesizing trees available for capturing and storing carbon dioxide. Some take this idea further by suggesting the burial of cut trees deep underground where the tree would not be subject to standard decay processes that re-release a tree's stored carbon. New trees could replace the buried trees, continuing the photosynthetic removal of carbon dioxide from the atmosphere. Biochar, a carbon-rich form of charcoal produced from burning vegetation without oxygen, could also be buried to store carbon.

Mineral Storage

Rocks accumulate carbon over time from rainwater through a process called geochemical weathering. By manually injecting carbon dioxide into basalt aquifers, carbon can be stored in rocks quickly. Absent an aquifer, the carbon dioxide needs to be injected with water. By storing carbon dioxide in minerals, the carbon dioxide is converted into a stable state that's difficult to convert back to carbon's greenhouse gas form.

The Pros and Cons of Geoengineering

Geoengineering is controversial due to the uncertainty of the effects of various geoengineering actions. While scientists rigorously study the potential effects of all potential geoengineering actions and often study geoengineering methods on small scales, there will always remain potential for unintended consequences. There are also legal and moral arguments for and against geoengineering in addition to international roadblocks to taking large-scale geoengineering actions. However, the potential benefits are also massive.

Benefits of Geoengineering

The various methods of solar geoengineering alone stand to return global temperatures to pre-industrial levels, which could directly benefit many parts of the planet affected by rapidly rising temperatures like coral reefs and melting ice sheets. Carbon dioxide geothermal engineering comes perhaps even higher potential rewards as it would target the cause of climate change at its source.

Consequences of Geoengineering

While geoengineering techniques aim to ameliorate the effects of climate change on the planet, there are known and unknown consequences to taking these large-scale actions. For example, lowering the Earth's temperature by reflecting the sun's solar radiation is expected to reduce precipitation around the world. In addition, the benefits of solar geoengineering are predicted to be lost if geoengineering stops.

Triggering massive algal blooms using iron is also known to have consequences. These artificially-induced blooms can disrupt the relative abundance of different types of algae, unbalancing the algae's natural community structure. These induced blooms can also allow toxin-producing algae to proliferate. Fertilizing the ocean, too, has so far been unsuccessful when attempted, although the idea still being rigorously studied with modifications.

Legal Interpretations of Geoengineering

The scale at which geoengineering would need to occur to meaningfully counteract climate change makes these ideas particularly challenging to implement. One of the main legal principles often invoked by those wary of geoengineering is the precautionary principle. The principle is generally interpreted to prohibit actions with uncertain outcomes that could have negative environmental consequences. However, some argue the precautionary principle is equally applicable to the continued release of greenhouse gases as the full effect of these emissions is unknown.

Restrictions to geoengineering may also apply under the United Nation's 1976 Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modifications Techniques (ENMOD), which outlaws creating environmental damage as a means of warfare. Geoengineering actions that could directly affect large regions of the planet could constitute "hostile use of environmental modifications" if actions are taken without the consent of all nations affected.

The legal treaties governing the use and ownership of space present similar challenges for the solar geoengineering planned for outside the atmosphere. Under the 1967 Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space Including the Moon and Other Celestial Bodies, or the Outer Space Treaty, the need for international cooperation for scientific endeavors, such as the addition of reflective devices, is indicated.