Aerosols and their impact on climate

Aerosols are small particles that float in the atmosphere. They can be produced by a number of sources, such as wildfires, volcanic eruptions, sea spray and air pollution. However, not all aerosols are alike when it comes to their impact on the climate.

Volcanic aerosols can be ejected very high into the atmosphere and even into the stratosphere, which allows these tiny particles to survive for as long as a few years. These volcanic aerosols reflect some of the sun's light back into space, which in turn means there is less of the sun's energy reaching the ground. The result can be a 0.7 to 0.9 of a degree Fahrenheit (0.4 to 0.5 of a degree Celsius) lowering of the Earth's average temperatures for as long as a few years. One example of this was the cooling impact from the Mount Pinatubo eruption in the Philippines back in 1991 (see image above).

Air pollution particles do not get nearly as high in the atmosphere compared to volcanic particles, thus their lifespan is much shorter (three to five days on average). However, air pollution in most areas is fairly constant, so these particles are continually replaced. Air pollution particles also reflect some of the sunlight, and this has a slight cooling effect. Back in the days before the Clean Air Act, there was much more air pollution over the United States, and this certainly had a cooling influence. After the Clean Air Act, there was a notable decrease in air pollution and an uptick in average temperature due to the decrease in air pollution aerosols in addition to climate change.

Wildfires, industry and diesel engines also produce soot, which is a heavier type of aerosol that can fall to the ground and collect on the surface. In areas that are snow or ice covered for much of the year, the accumulation of soot can have significant impacts on regional temperatures. The darker-colored soot that accumulates on the snow and ice leads to a lowering of the albedo, which in turn means more of the sun's energy gets absorbed at the surface, causing an increase in temperature.

Overall, aerosol pollution has made the planet about 0.7 of a degree Fahrenheit (0.4 of a degree Celsius) cooler than it otherwise would be; however, greenhouse gas emissions have made our planet 2.7 F (1.5 C) warmer than it otherwise would be, leading to a net gain of warming, according to the NASA report.