Department of Climate and Space Sciences and Engineering in the College of Engineering at the University of Michigan


AOSS Professor Penner: Move beyond CO2 to better understand climate change

Posted: August 2, 2010

AOSS Professor Penner: Move beyond CO2 to better understand climate change

Scientists and policymakers should look beyond carbon dioxide for strategies to curb and to understand global warming, say a group of high-profile climate scientists led by AOSS professor Joyce Penner.

Penner is a professor in the Department of Atmospheric, Oceanic and Space Sciences. She and several colleagues outline their arguments in a commentary newly published online at Nature Geoscience.

They argue that reducing emissions of short-lived greenhouse gases and black-carbon aerosols, as well as quantifying their effects on the climate, could mitigate global warming in the short-term and improve long-term climate predictions.

Short-lived pollutants can have an atmospheric lifetime of less than two months (though methane has a lifetime of about a decade). Carbon dioxide, by contrast, can stay in the atmosphere for more than a century.

Some short-lived pollutants are known to contribute to global warming. These include methane, low-atmosphere ozone, and black carbon, also known as soot. The researchers say these should be actively curbed, both to reduce warming and to provide insights and the time to understand how the remaining pollutants are impacting the climate. Most climate policy proposals have focused on reducing carbon dioxide.

The climate effects of other short-term pollutants, including nitrogen oxides, carbon monoxide and volatile organic compounds, are still uncertain.

And an important class of short-lived gases actually decreases the warming effect of carbon dioxide. These include sulphate, nitrate and organic aerosols. But scientists don't fully understand the extent of their cooling effects.

If researchers can determine the roles of all of these transient gases, Penner says, that will help them figure out just how sensitive the planet's climate is. During the past 100 years, has the climate been highly sensitive to CO2 build-up, in which case the cooling pollutants would have acted like air conditioning on full blast? Or is the climate minimally sensitive and the veritable a/c on low?

"These two possibilities lead to very different projections for future climate change," the commentary states. "We argue that to distinguish between these possibilities, and to provide short-term relief from climate warming, the short-lived compounds that induce warming need to be brought under control within a timescale of a few decades."

Penner will be a review editor of a chapter in the International Panel on Climate Change's Fifth Assessment Report, due out in 2014. She was the lead author of a chapter in the 2007 report for which the United Nations-sponsored panel shared the Nobel Peace Prize with former Vice President Al Gore.


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