Somewhere in Joyce Penner’s office, perhaps under a pile of papers, is a Nobel Peace Prize certificate that recognizes her work with the United Nations Intergovernmental Panel on Climate Change.
“The certificate is actually quite nice; I really should get it framed,” says Penner, the Ralph J. Cicerone Distinguished University Professor of Atmospheric Science and CLASP associate chair for atmospheric science.
Penner has coordinated and contributed to IPCC climate reports since 1994 and was lead author on the report for which the group shared the 2007 Nobel Peace Prize with Al Gore. She led the compilation of the 2001 report’s chapter on aerosols – the fine, tiny bits of solid and liquid suspended in the atmosphere and in the air we breathe. She was on stage at the final summary meeting as the report on Aviation and the Global Environment was edited and tweaked, sentence-by-sentence, to satisfy the disparate tribes of scientists and policymakers.
The aerosols Penner studies constitute things like fog, haze and air pollution. In the atmosphere they affect the way clouds form and reflect solar radiation, resulting in a cooling effect that can mask the warming from greenhouse gasses. Penner develops mathematical and computer models to help us better understand what how aerosols and clouds interact and how that affects the climate.
These aerosol-cloud interactions represent one of the least-understood areas in climate science. Much of what we do know has come through Penner’s efforts to fine-tune the global climate model with equations that help give a clearer picture of the mechanisms that affect climate.
There are plenty of unknowns. But the unknowns, she says, don’t change the bottom line.
“The Greenland ice cap is breaking apart,” she said. “So is the Western Antarctic ice cap. If those break off you could lose some low island nations and get rid of one-third of Florida.”
Penner, who has a masters and PhD in applied mathematics from Harvard, started out working in atmospheric chemistry in the late 1970s, when chlorofluorocarbons were destroying the ozone layer in the atmosphere. Early on, she found ways to represent what was happening chemically in global climate models. When aerosols emerged as an important factor in the early 1980s she had the chemistry-based expertise to incorporate them into the global model. By the time she came to Michigan from the Lawrence Livermore National Laboratory in California in 1996, she’d already turned her attention to aerosols.
“I started looking at what they do to climate, and that has just expanded.” she said. “It always excites me when there are unknowns and when you think, by applying the tools we have, we can shed light on these unknowns.”
Though humans control the biggest sources of aerosols in the atmosphere by virtue of the fossil fuels we burn, volcanic eruptions and an ocean algae called phytoplankton also contribute to the aerosol load. Some advocate geoengineering – purposefully releasing aerosols into the atmosphere in order to offset the warming effect of carbon emissions. But Penner cautions against relying on geoengineering to save the day.
“As time goes on, the situation will be more and more obvious to everyone that something is going on and we need to do something,” she said. “We need to cut greenhouse gas emissions; we need to decarbonize the energy system.
“People say, ‘It’s only a 3-4 degree Celsius change by 2100. What’s the big deal?’ Well, it’s the difference between living in Michigan and living in Arkansas.…It’s an extremely difficult problem because time keeps marching on, emissions keep growing, and the whole problem gets harder.”
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