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Small Particles, Big Impact

by Daniel Huffman

From the wildfires Australia to the flooding of Indonesia, the symptoms of the climate crisis are now here, and serve as warnings of even worse to come. It is common knowledge that the emission of greenhouse gases, especially carbon dioxide and methane, are to blame for the planet’s rise in temperature, and hence there is an almost universal consensus that a reduction in fossil fuel combustion is necessary to lessen the effects of the climate crisis. At the same time, however, it is true that some of our emissions have a more complicated relationship with climate, and thus the optimal course of action may not seem as straightforward.

Much like greenhouse gases, liquid and solid particles present in the atmosphere, called aerosols, carry significant implications for earth’s climate. While many of the aerosols in the atmosphere, such as those resulting from organic plant emissions or volcanic eruptions, are of natural origin, the excess particles are of anthropogenic origin. With sources ranging from hairspray to the combustion of fossil fuels, aerosols are yet another type of substance propagating beyond their natural concentration due to human actions. Now, as society is growing more aware of how its emissions impact the climate and environment, scientists are increasingly interested in researching the effects that this specific class of substance has on climate and what implications it may have on efforts to combat the climate crisis.

Once aerosols are emitted, whether it be through natural or anthropogenic means, they typically make their way into the lower atmosphere, where they may remain for a few days or weeks. While in the atmosphere, aerosols produce a variety of effects. For one, aerosols tend to reflect sunlight directly away from the earth’s surface, reducing the extent to which solar radiation is absorbed as heat. Moreover, certain aerosols are critical to the formation of clouds, especially those closer to the earth’s surface. While clouds exhibit a range of effects on temperature depending on their size and location, those lower in altitude predominantly cool the surface through the reflection of incoming solar radiation. Thus, the net effect of aerosol emissions has been that of a lowering in global temperature, which some scientists estimate to be on the range of 0.5 to 1.1 degree Celsius.

Since the presence of aerosols in the atmosphere induces a net cooling effect, the natural result of removing said aerosols would likely be an increase in temperature. This projection has driven many to rationalize that a reduction in fossil fuel consumption would serve the opposite of its intended effect, shrinking the supply of aerosols to the atmosphere and diminishing their cooling potential. However, as a recent study in Nature suggests, the interval over which the phaseout of fossil fuels takes place may prevent such a drastic spike in temperature from occurring. While most considerations of this phenomenon assumed an immediate removal of emissions, Shindell and Smith modeled the resulting warming that would occur if emissions were reduced at rates that coincided with the pathways to 1.5 degrees Celsius of warming listed in the International Panel on Climate Change’s 2018 report. Their findings demonstrated that a realistic phaseout in emissions would still result in an increase in temperature, though the extent of warming due to the removed aerosols would likely be lower than half a degree.

                Although they may not contribute to global warming as greenhouse gases do, aerosols are just as dangerous in regards to health. Due to their miniscule size, aerosols may easily enter the body through inhalation or other means, potentially damaging one’s cardiovascular system and leading to the contraction of potentially fatal diseases. The proliferation of aerosols due to daily activities such as driving automobiles results in nearly inevitable human exposure, putting virtually everyone at risk. In fact, air pollution, largely consisting of aerosols, was the fourth leading cause of death as of 2016, responsible for approximately 5.5 million deaths per year. Consequently, despite the warming that may occur as a result, eliminating anthropogenic aerosol emissions is a necessary measure to improve public health.

                As we begin to address the climate crisis head-on, it is useful to consider the full range of effects a reduction in emissions will entail. Although the presence of aerosols in the atmosphere counters the rapid warming of the earth to some extent, a reduction in atmospheric aerosol concentration may not necessarily result in a spike in global temperatures. Further, the danger aerosols and other forms of air pollution pose to public health emphasizes the need to cut emissions of such chemicals. Allowing fossil fuel usage to continue under the guise of preserving the aerosol masking effect would produce greater warming than a reduction in aerosol concentration ever would, and accordingly, we must not hesitate to curb emissions for the sake of our planet.