advancing the mitigation of Climate Change and Global Warming through Geoengineering education and research
Solar Radiation Management
What is Solar Radiation Management?
Solar radiation management or solar geoengineering is a large category of diverse climate engineering approaches that mitigate or reverse Global Warming by reflecting sunlight (i.e., solar radiation/shortwave radiation) into space before it is absorbed by the environment and converted into heat (i.e., transformed solar radiation, thermal radiation, thermal motion of particles, vibrational energy or longwave radiation). These approaches include:
Solar radiation management also has approaches that try to move heat away from the Earth’s surface and/or outside our atmosphere (into space). These approaches are known as Earth Radiation Management. For a summary of Earth Radiation Management approaches, please see
Solar Radiation Management Background
Solar radiation is electromagnetic radiation (Figure 1) emitted by the sun. The sun emits wavelengths of radiation from radio waves to gamma rays. Most of the radiation produced by the sun is energy emitted by nuclear fusion reactions.
Figure 1. The electromagnetic spectrum. Courtesy of NASA.
Although the sun does produce small amounts of radio waves, x-rays and gamma rays, the vast majority of the radiation emitted is in wavelengths between 0.25 and 2.4 µm (microns or micrometers/which is one millionth of a meter). The solar spectrum (the solar radiation that hits the Earth’s upper atmosphere) includes infrared (52-55%), visible light (42-43%) and ultraviolet (3-5%) (Figure 2).
Figure 2. The Solar Spectrum. Courtesy of NASA and Geoengineering.global.
Solar radiation is continually bombarding our planet with both life-giving light as well as harmful radiation. Much of the harmful radiation is absorbed, deflected, reflected, or scattered in the Earth’s magnetic field and upper atmosphere before it hits the ground (Figures 3 and 4). Interactions include:
- The Earth’s atmosphere absorbs and prevents gamma rays (produced from solar flares) from hitting the surface of the planet.
- X-Rays are completely blocked by ozone in the stratosphere.
- Electromagnetic radiation with wavelengths longer than radio waves are completely blocked by electric charges in the upper atmosphere.
- Ozone (O3) and oxygen molecules (O2) in the upper atmosphere absorb most of the ultraviolet radiation below 0.3 micrometers.
As seen in Figures 3 and 4, visible light, near ultraviolet, near infrared and radio waves do penetrate our atmosphere and reach the ground.
Figure 3. Absorption of solar radiation in the atmosphere. Courtesy of Geoengineering.global. Images of the Sun and Earth courtesy of NASA.
Figure 4. Absorption of solar radiation in the atmosphere. Courtesy of the University of Chicago.
As mentioned above (See Figure 2), most of the solar radiation that penetrates our atmosphere and reaches the ground is in wavelengths between 0.25 and 2.4 µm (or 250 to 2400 nanometers) (Figure 5). This spectrum of solar radiation that reaches the ground includes infrared (52-55%/700-2400 nm), visible light (42-43%/400-700 nm) and ultraviolet (3-5%/250-400 nm) wavelengths.
As can be seen in Figure 5, the solar radiation that hits the ground (i.e., sea level) (shown in red) is about 70% of the radiation that hits the top of the atmosphere (shown in yellow). As can be seen in the figure, atmospheric ozone (O3), oxygen molecules (O2), water vapor (H2O) and carbon dioxide (CO2) (called atmospheric absorption bands in the figure) reflect 30% of this incoming solar radiation back into space and prevent it from reaching the ground.
Figure 5. The spectrum of solar radiation at the top of the atmosphere (yellow) and at sea level (red). Courtesy of Robert A. Rohde and the Global Warming Art Project.
The Earth’s Energy Budget (Figure 6) is a scientific model that quantifies the energy (i.e., solar radiation) that the Earth receives from the Sun and the pathways this energy takes as it interacts with and flows through the Earth’s geosphere before it travels back into space.
In the model, 30% (atmosphere (6%) + clouds (20%) + Earth’s surface (4%)) of the incoming solar radiation (shortwave radiation) is reflected back into space before it is converted to heat (thermal radiation or longwave radiation). After entering the Earth’s atmosphere, the remaining 70% of this solar radiation is absorbed (and converted into heat) by the land and oceans (51%), the atmosphere (16%) and clouds (3%). After the conversion to heat, all of this heat (which is the entire product of the conversion of the 70% of incoming solar radiation) radiates back to space through several pathways. This model, in essence, shows that that all the energy that enters the Earth’s geosphere leaves the geosphere.
Based on the fact that the Earth’s atmosphere, lands and oceans are heating up, it is logical to think that perhaps the solar energy coming into the Earth’s geosphere is larger than what is leaving the geosphere (perhaps this is not represented in the model because the imbalance(s) in the energy pathways are very small and the model rounds all the pathways to whole numbers). This imbalance is resulting in Global Warming which is being caused by carbon dioxide emissions and the Greenhouse Effect.
The pathways depicted in this Earth’s Energy Budget model are the focus of Solar Radiation Management Geoengineering. Solar Radiation Management approaches attempt to cool the planet by either reducing incoming solar radiation, reflecting solar radiation into space before it is converted into heat or transferring or moving heat away from the surface of the planet to protect the areas of the Earth that support life (i.e., the biosphere).
Figure 6. The Earth’s Energy Budget. Courtesy of NASA GPM.