Stuart Evans researches how airborne sediments can impact climate, influencing patterns of precipitation & drought
University at Buffalo researcher Stuart Evans studies dust – not the balls of stale gray fluff that collect under your bed, but the tiny bits of mostly reflective material that hang in the Earth’s atmosphere, influencing weather conditions like temperature, rain and wind.
It’s a curious field of study that matters a lot – especially as the planet’s climate changes.
“The level of dust in the air can have far-reaching effects on climate, but there are still a lot of unknowns in the field,” said Evans, Ph.D., an atmospheric scientist who is an assistant professor of geography in the UB College of Arts and Sciences and a faculty member in the UB RENEW (Research and Education in eNergy, Environment and Water) Institute.
“I’m interested in fundamental questions about precipitation and drought,” Evans said. “How does the atmosphere respond to dust? Where does the rain move as the levels of dust change? How does the timing of the wet season change?”
What is Dust?
Though the word “dust” may conjure images of nebulous masses of matter, the term, as applied in Evans’ work, refers to something quite specific.
The dust he studies consists of particles of clay and minerals that have been ground up into pieces so small that they can stay aloft for days or even weeks once they’ve been whipped into the air. Most of this sediment comes from ancient lake beds that have since gone dry.
Another form of airborne debris – ash from wildfires or industrial combustion – doesn’t count as dust in Evans’ line of work.
“In my field of research, you don’t get dust from burning things. You get dust from ground up rocks,” he said.
“One reason we want to make this distinction is because different types of particles have different climate impacts,” he added. “So if you have dark particles, they tend to heat the Earth, and white particles tend to cool the earth. So something like a wildfire puts all this black soot into the air, and it makes things slightly warmer. Sea salt is the other end of the spectrum. It’s highly reflective. Dust falls somewhere in the middle — it consists of mostly reflective bits of fine sediment that can be picked up by the wind and carried for long distances.”
Dust and Rainfall
Evans uses computational modeling and satellite observations to study how dust impacts climate. He has researched some of the dustiest places on the planet, including the Sahara and the Sahel in Africa.
Evans explained that, by scattering and absorbing sunlight, dust can alter the temperature of the Earth’s surface, which can, in turn, impact rainfall and, eventually, plant growth in a region.
One example of how this might happen: “Most thunderstorms start with a hot surface and rising air,” Evans said. “If you make the surface cooler, you get less of this rising air as a result. That makes for less rain. In a place like the Sahel, it can weaken the monsoon. This is important because this is a region of the world where even small changes in rainfall can have large impacts on agriculture and people.”
As the planet gets warmer, Evans is interested in how a reduction in rainfall might create a feedback loop in some areas, where a loss of precipitation could cause increased dust, leading to even lower levels of rain.
“Dust is really interesting, and as a field of study, we have still have a lot of fairly fundamental questions we can ask,” Evans said.
“I’m a physical scientist, so I want to know how the Earth works,” he added. “Dust is a part of that. If you look at the geologic record, there have been times in the Earth’s history where there’s wildy more or less dust. There have also been times where you have an asymmetry between the amount of dust in the Northern and Southern Hemispheres. How does all of this affect climate?”