Techniques that intentionally change the Earth’s climate, such as geoengineering and cloud seeds, are following the devastating floods in Texas. Although these approaches offer potential for rapid response to certain climate risks, they also bring significant uncertainty, moral considerations, and risks of unexpected environmental consequences. Kara D. Lamb, an associate research scientist in the Department of Earth and Environmental Engineering, introduced the science of geographic engineering and weather modification in the following interview and discussed their impact on future climate mitigation strategies.
What is geoengineering?
Climate geoengineering refers to many large-scale technologies used to reduce the impact of climate change. Some approaches focus on reducing greenhouse gases in the atmosphere, such as through direct carbon capture or targeting methane, a powerful greenhouse gas. Another approach mentioned under the umbrella of Solar Radiation Management (SRM) is designed to increase the reflection of sunlight in the Earth’s atmosphere to cool the Earth’s climate. The most common study of these methods is stratospheric aerosol injection, which recommends sulphate aerosols being placed in the Earth’s atmosphere to cool the climate (this is similar to the cooling effects observed after large volcanic eruptions, such as Mount Pinatumo in 1991). Another method widely studied is ocean cloud brightness. The technology targets low clouds formed on the ocean and proposes to make these clouds brighter so that more sunlight can be reflected back to space. The SRM method is primarily studied by modeling or in the laboratory and is not deployed in any large-scale atmosphere.
Stratospheric aerosol injection (SAI): Strategy to increase the number of small and medium-sized reflective aerosols in the stratosphere to increase the reflection of incoming sunlight.
Ocean Cloud Bright (MCB): Strategy for increasing aerosols in marine areas to increase the reflectivity of low-lying ocean clouds.
Cirrus cloud sparse (CCT): A strategy to modify the characteristics of high-altitude ice clouds to increase the propagation of land radiation into space.
Space method: The proposed method mainly considers large “mirrors” in the space to reflect the sunlight.
Surface albedo enhancement: The reflectivity of the surface is increased by, for example, changes in white roofs or land cover.
What are cloud seeds and how to practice today?
Since the 1940s, cloud seeds have been used to increase precipitation and snow accumulation. This is often called a “weather modification” because the focus is on short-term (on-hour scale) increasing rainfall or snowfall. It is used in many states in the western United States, with concerns over drought and many other countries around the world.
There are many different weather modification methods and methods. Earlier this year, my colleague Jared Donohue and I conducted a study to create datasets of recent weather modification usage in the United States by compiling publicly available records. Our paper is still under review, but we found that the most common method in the western United States is to use silver iodide deployed by airplanes or ground cannons to increase snow accumulation. Iodide particles are dispersed in the clouds and under certain conditions, the amount of precipitation produced (snow or rain) can be slightly increased.
How effective is cloud seeds, and it may help with floods or other extreme weather?
It is difficult to tell exactly how cloud seeds work, because the weather naturally changes greatly, and the exact amount of rain or snowfall in a given area is difficult to predict. However, based on our knowledge of cloud and rainwater forms, the condensation of cloud seeds does not significantly increase precipitation. Most studies show that it may only increase precipitation by 5-15% compared to the absence of cloud seeds.
What problems arise when we consider using geoengineering to manipulate the earth’s climate?
We know that SRM will not simply eliminate warming due to greenhouse gases (the atmosphere is much more complicated than this), so it is not a substitute for reducing greenhouse gas emissions. And there are moral issues, because SRM has the potential to benefit more than other regions. Our current model is not accurate enough to fully understand and predict what these regional impacts may be, and therefore requires improved scientific understanding and governance frameworks to address such challenges.
Is geoengineering a promising approach to climate change?
Interest in climate geoengineering has regained interest, a potential way to reduce the direct impact of climate change, while long-term solutions to reduce greenhouse gases are to reduce climate change. While we still need to learn a lot, doing research in this area helps us better understand how the atmosphere works, which is very important for understanding the weather and climate. Therefore, these areas certainly require further research, but we are not yet at the stage where we should consider large-scale adoption of geoengineering and should not disperse the need to reduce greenhouse gases.
