Modeling the atmosphere is very difficult because there are so many different interactions that have to be considered. It's like trying to put together a gigantic jigsaw puzzle.

Karen Castle

Climate change is one of the most pressing issues of our time. For Professor Karen Castle, chemistry, understanding this complex topic is looking up. Way up.

Castle studies the physical and chemical processes in Earth's upper atmosphere, roughly 60 to 120 kilometers above Earth’s surface. As in the lower atmosphere, levels of greenhouse gases such as carbon dioxide have increased in the upper atmosphere. Rather than warming, however, their effect in the upper atmosphere is cooler temperatures.

"Since the 1960s we've seen about a 12-degree Celsius decrease in temperature at altitudes of 300 kilometers," Castle says, which represents a significant change in a region that is normally very stable. Along with the temperature changes come shifts in atmospheric density. This rapid response to minute changes in greenhouse gas concentrations means that monitoring conditions in the upper atmosphere could provide an early indicator of climate-changing processes taking place in the lower atmosphere.

Castle and her students use a technique called laser spectroscopy to measure the kinetics of energy transfer in collisions between different gases in the laboratory. The results will inform climate models. "Modeling the atmosphere is very difficult because there are so many different interactions that have to be considered," she says. "It's like trying to put together a gigantic jigsaw puzzle. The problem modelers face is that up to one-third of the pieces of their puzzle are not defined very well. My group tries to work on individual pieces of the puzzle to help make the modelers' job a little easier."

Castle's work has implications not only for climate change, but also for the design of space vehicles that travel through the upper atmosphere and for interpreting data retrieved by certain NASA satellite missions. Funded by NASA, she also studies energy-transfer mechanisms that are important for Martian atmospheric models. She is also pursuing exploratory research related to the atmospheres of Venus and Titan, the largest moon of Saturn.

Castle involves her students directly in her research. A co-founder of the Discovery Residential College, she has mentored dozens of research students, all of whom have presented their work at local, regional or national research symposia. She aims to take at least one student to a national meeting of the American Chemical Society every year.

“When you work in a research lab, you need to work toward something,” Castle says. “It’s nice for the students to have concrete goals, such as the chance to present their results to experts in the field. They make a lot more progress on their projects knowing that’s an experience that they’ll get to have. Plus it’s part of the culture here; research is a thing our students and our faculty members want to do.”

Updated Sept. 23, 2016