MSU professor studies green roof carbon absorption

Green roofs are sprouting up on building tops across the U.S., a growth some MSU researchers say could combat the rising amount of carbon dioxide being released into the atmosphere.

Horticulture professor Brad Rowe and doctoral horticulture research assistant Kristin Getter led a two-year study measuring the amount of carbon that various green roofs could sequester, or remove from the atmosphere through photosynthesis.

Traditionally, Rowe said people decide to transform their rooftops into green roofs to cut their summer energy bills.

According to the study, which was published Aug. 25 online in the science journal Environmental Science & Technology green roofs could capture more than 55,000 tons of carbon in an urban area with a population of about one million people. No numerical data on green roofs’ ability to sequester carbon existed prior to Rowe and Getter’s study, Rowe said.

“A lot of people believe carbon dioxide in the atmosphere has increased significantly in the last couple of years and is one of the main causes for global warming,” he said. “There’s been nothing published on carbon sequestration (and how green roofs can impact it).”

In the second experiment in the study, 20 plots of sedum, a drought-tolerant plant species, were placed on the roof of the Plant and Soil Sciences Building, Rowe said. Each plot was 10 square feet. Rowe and Getter took measurements throughout the year for three sections of the plots — above-ground roots and shoots, below-ground roots and the plot’s media — to see how the amount of captured carbon changed over time.

Rowe said the 375 grams per square meter the green roof system sequestered in above- and below-ground roots and shoots is a small amount for the area studied, but it’s better than a traditional roof’s carbon sequestration.

“The number 375 grams per square meter isn’t very much, but it’s … something,” Rowe said. “Just a plain roof is basically nothing.”

Additional research on the different styles of green roofs and plant species began in the summer, Rowe said.

Leigh Whittinghill, a doctoral horticulture student who Rowe advises, is one of a number of people involved in the follow-up study. Continued green roof research will be a necessary step for the U.S. if it hopes to catch up to other countries’ green roof research, Whittinghill said.

“At the moment, the green roof industry in the United States is fairly young compared to other countries,” Whittinghill said. “Green roof is a really important tool we can use to help combat some issues we’re having, especially in our urban areas.”

Steven Peck, president and founder of Green Roofs for Healthy Cities, said the ongoing research in the Green Roof Research Program at MSU will play an important role in expanding the industry.

Green Roofs for Healthy Cities is a Toronto-based nonprofit industry association, according to the group’s Web site, greenroofs.org.

“Brad Rowe has been at the forefront of green roof research, specifically on the plant side,” Peck said. “We need green roof research on different scales to advance the industry.”