Loretta MickleyProjected annual mean surface temperatures in the eastern United States. The green lines represent temperatures with no change in present-day aerosol levels; the red lines indicate what temperatures would be if aerosols were absent from 2010 onward.
When you hear the word aerosol, a can of hairspray, spray paint or whipped cream may come to mind.
But technically an aerosol is any suspension of liquid or solid particles in a gas. And both natural aerosols, resulting from phenomena like erupting volcanoes or desert winds, and manmade aerosols, like those from crop spraying or burning coal, can have serious climate implications — far more serious than whether your hair stays in place for 12 hours after that squirt of hair spray.
After Mount Pinatubo in the Philippines erupted in 1991, the massive plume of ash it sent into the sky cooled global surface temperatures by about 1 degree Celsius (1.8 degrees Fahrenheit) for a year.
Atmospheric aerosols affect the climate directly, through the scattering and absorption of sunlight, and indirectly, by functioning as seeds for cloud formation. Injecting aerosols into the atmosphere is one of the most hotly debated geo-engineering strategies put forward to combat climate change.
Over the last century, anthropogenic aerosols from industrialization have partly offset the warming effect associated with rising greenhouse gas emissions related to human activity.
In the United States, however, campaigns to improve air quality and reduce acid rain have led to a sharp decline in atmospheric aerosols. Since 1980, for example, the amount of sulfur dioxide produced by coal plants has dropped by 83 percent. While this trend has clear health benefits, it has also been implicated in regional warming consequences.
Relying on given climate predictions for 2010 to 2050 from the Intergovernmental Panel on Climate Change, a team of scientists recently set out to investigate the potential climate consequences of eliminating atmospheric aerosols in the eastern United States. The team, led by Loretta Mickley, an atmospheric chemist at Harvard, used a high-resolution computer model developed at NASA‘s Goddard Institute for Space Studies.
“We knew there was an experiment going on in the atmosphere over the eastern U.S., and we wanted to know what regional climate response would result,” Dr. Mickley said.
In an article in the Atmospheric Environment journal, she and her colleagues projected that the elimination of atmospheric aerosols over the eastern United States would increase ground temperatures across the region by 0.4 to 0.6 degrees Celsius (0.7 to 1.1 degrees Fahrenheit) and increase the severity of heat waves by 1 to 2 degrees Celsius (1.8 to 3.6 degrees Fahrenheit). The rise was driven by positive feedback related to drier soils and less low cloud cover.
The estimates are conservative, given that the model only analyzed the direct effects of aerosols on climate; including indirect effects would have led to an even greater predicted warming.
While no one is suggesting that the nation revert to the air quality standards of the 1960s, experts say that the study highlights how cleaning up our act when it comes to aerosols is just the beginning of thinking through the changes that may be needed to protect the planet’s inhabitants.
