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How Anthropogenic Aerosols Have an Impact on Global Warming

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Scientists have discovered a new technique, called Solar Radiation management, or SRM, as a proposed method of cutting down on greenhouse gases and the resulting atmospheric warming that occurs. Inspired by cooling that resulted after volcanic eruptions, research and debate on how we can reduce the effects of anthropogenic aerosols in our environment is now becoming a tool for manually altering the climate.

Aerosols are most often used to describe a substance under pressure to be dispersed in a can with a nozzle of some sort, like a can of spray paint. However, from a scientific perspective, aerosols refer to either naturally occurring or anthropogenic (man-made) particles suspended in the atmosphere. Natural aerosols are substances like fog or dust, while anthropogenic aerosols are potentially harmful pollutants like fossil fuels. Scientists have recently discovered that a higher natural aerosol background can in fact reduce the negative impacts of anthropogenic aerosols, such as a rise in global warming and greenhouse gases (Spracklen, 2013). Through a better understanding of natural and man-made aerosols, scientists will be able to replicate the impacts of natural aerosols. Aerosols caused from natural sources, such as volcanoes and wildfires have actually reduced the effects of man-made aerosols that come from sources such as coal-burning power plants. Scientists are hypothesizing that they can deliberately use aerosols to fight climate change (Robock, 2013, pp. 445-458). Studying the natural aerosol particles in the atmosphere can provide insight into how to geoengineer climate change to our benefit (Harvey, 2018).

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Scientists have recently discovered that cleaning up anthropogenic aerosols (predominantly sulfate) in our biosphere could actually add a half degree of global warming, and strengthen the effects of greenhouse gases (Samset, 2018). Thus, it is important how we go about reversing pollution in the climate.

Global warming should be kept within 1.5 or 2 degrees Celsius, which requires “strong mitigation of anthropogenic greenhouse gas (GHG) emissions (Samset, 2018). This just means that to limit global warming, a harsh decrease in human caused greenhouse gases is necessary. If this occurred, anthropogenic aerosol emissions would decrease from the climate as well. However, the act of removing aerosols would cause the global surface temperature to increase between 0.5 and 1.1 degrees Celsius, and precipitation to globally increase overall 2.0-4.6%. Aerosols can effectively cool the earth by reflecting sunlight (Samset, 2018). Therefore, to slow global warming, we must maintain a balance between greenhouse gas emission and aerosol levels.

Geoengineering is a process to combat climate change, which a few scientists have begun to explore which involves manipulating various aspects of the planet (Harvey, 2018). It has proven to be very controversial in the science community; some believe that manipulating the environment like this could have unintended side effects like altering weather patterns. Others claim that we should focus on preventing further damage with political efforts, rather than introducing new technology to try and reverse damage already done. Still other scientists argue that Geoengineering is not a replacement for “traditional” efforts to prevent climate change (like recycling or using wind turbines) but rather a supplement to enhance current plans as well as serve as a backup plan.

Scientists at Harvard are experimenting with stratospheric aerosols to attempt to understand Geoengineering further. The experiment, Stratospheric Controlled Perturbation Experiment (SCoPEx), is intended to take qualitative measurements on the physics and chemistry of aerosols in our environment to understand the risks or benefits of Geoengineering in a large scale (Dykema, 2014). The experiment’s principal Investigator, Frank Keutsch, Stonington Professor of Engineering and Atmospheric Science and Professor of Chemistry and Chemical Biology along with a small team of four hope to measure on a small scale how aerosols affect stratospheric chemistry, to apply research to large-scale global models, and then understand more about Geoengineering the stratospheric ozone. They explain, “SCoPEx will address questions about how particles interact with one another, with the background stratospheric air, and with solar and infrared radiation. Improved understanding of these processes will help answer applied questions such as, is it possible to find aerosols that can reduce or eliminate ozone loss, without increasing other physical risks?” The experiment will be conducted by propelling a balloon into the atmosphere that will introduce particles to the air. It creates a small, controlled sample of stratospheric air to observe the effects over time.

Frank Keutsch, the pioneer of the experiment is also head of a research group at Harvard called the Keutsch group. They focus on aerosols, and understanding how secondary pollutants affect human health and the climate. They have found that although the long-term effects of aerosols are not certain; they are responsible for the anthropogenic state of our current climate. They hope to understand the process of photochemical oxidation of volatile organic compounds (VOCs) (Keutsch Research Group, 2018). VOCs are pollutants found both indoors and outdoors, that are released as a product of mechanization (or “ photochemical oxidation”). The United States Environmental Protection Agency limits these VOCs because they are known for creating smog, or secondary organic aerosols (SOAs) (United States, Environmental Protection Agency). The Keutsch group specifically targets Formaldehyde and a-dicarbonyls, which are especially important to SOA formation (Keutsch Research Group, 2018).

Scientists have been researching this phenomenon for decades, with inspiration from natural occurrences, like volcanic eruptions. Mount Pinatubo, a volcano in the Philippines, erupted in 1991 and caused cooling in the climate. Scientists claimed that this was not, in fact, caused by a dust cloud following the eruption, but sulfur dioxide that was released that reflected and scattered sunlight. This was seen as “natural Geoengineering” (a phrase which is actually contradictory, because Geoengineering by its nature is caused by man). This also occurred in 1982 when El Chichon erupted in Mexico, causing a small decrease in global temperatures until the warming trend resumed around 1986. The eruption of Mount Pinatubo was much larger than El Chichon, so experts like Dr. Alan Robock, a meteorologist at the University of Maryland who focuses on volcanoes and climate proposed that heat trapping anthropogenic aerosols like carbon dioxide are dispersed with the introduction of aerosols caused by the volcanic eruption. (Stevens, 1991). As these scientists predicted, the eruption of Pinatubo in 1991 dropped global temperatures by about one degree Fahrenheit. This natural event served as an inspiration for the Geoengineering experiments focusing on VOCs in the years to come. Proposed ideas for solar radiation management or S.R.M. that mimic the effects of eruptions such as spraying chemicals into the stratosphere with jets still require research and understanding of the long term effects of Geoengineering. NASA researchers led by Paul A. Newman are doing so by measuring sulfur dioxide in the air before and after a volcanic eruption similar to Pinatubo. By monitoring the aerosols over time, they can see how different sizes of aerosols could stay in the atmosphere for longer or shorter amounts of time, maximizing the effects of reflective aerosols (Fountain, 2018).

While Geoengineering has been seen as a risky measure to minimize the effects of greenhouse gases, it has become less taboo in recent years with an influx of scientists studying in the field. The public tide has shifted from attempting to prevent further greenhouse gas emission, but using technology to try to combat greenhouse gases already present. The American Geophysical Union (or AGU) made a statement this past January endorsing climate intervention in collaboration with the American Meteorological Society. They defined climate intervention as a “deliberate large-scale manipulation of the planetary environment to counteract anthropogenic climate change,” and stated the two most plausible approaches to climate change. The first category is carbon dioxide removal, which is the use of technology to directly remove CO2. The second category of climate intervention is albedo modification (AM), another way of describing putting aerosols into the upper atmosphere to reflect sunlight away from the planet, cooling the climate. The AGU stated:

AM cannot substitute for reductions in greenhouse gas emissions, because its effects on the climate are not simply to reverse warming and because it would have no direct effect on ocean acidification caused by increasing carbon dioxide levels. However, in theory, it could reduce some harm done by climate change during the time it takes for societies to implement deep cuts in greenhouse gas emissions while also potentially developing and deploying CDR systems. It could also, in theory, cool the climate quickly and thus proves highly valuable should society at some point face rapid changes in climate that cause unacceptable damage.

The perception towards preventing climate change has, in fact, reached urgent measures. While outdoor experiments could have problematic results, a last-resort attempt has become the new focus.

Solar Radiation management, or SRM, has become a forefront in scientific research to cut down on greenhouse gases and the resulting atmospheric warming that occurs. Natural inspiration such as cooling that resulted after volcanic eruptions has sparked research and debate on how we can reduce the effects of anthropogenic in our environment, but reflecting sunlight away from the earth.


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