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Aslam Khalil
Aslam Khalil

From Source to Sky

Tracking greenhouse gases

Physics professor Aslam Khalil has shaped scientific understanding of global climate change. He was one of the first to identify methane's role as a powerful greenhouse gas, tracing its increase to human activities such as rice farming. Establishing these connections has proven crucial in the battle to alter behaviors that contribute to global warming.


Scientists have long understood that carbon dioxide (CO2) in the atmosphere contributes to the “greenhouse effect”—a trapping of energy that results in higher temperatures.

But it was research by atmospheric physicist Aslam Khalil that in 1981 first recognized the rapid increase of another gas in the atmosphere 20 times more potent than CO2: methane.

Khalil, now a professor of physics at Portland State University, is one of the field’s most widely cited experts, as he has worked to understand methane and other greenhouse gases, their sources, and the human and natural behaviors producing them.

In China, farmers began planting a hybrid breed of rice that needed less water. That allowed for periodic draining of rice paddies. By not leaving land flooded year-round, and alternating other crops, Khalil and others found that farmers reduced the anaerobic conditions that produce methane.

His body of work led to the inclusion of a half-dozen greenhouse gases in the 1997 Kyoto Protocol. Over 190 countries worldwide (though not the United States) eventually adopted the international environmental treaty aimed at monitoring and curtailing greenhouse gas emissions.

Much of Khalil’s recent work has focused on methane—a gas 20 times more effective at trapping heat than CO2. As populations grow and urbanize, methane production increases. Seemingly paradoxically, global methane levels in the atmosphere have stabilized over the past two decades even as concentrations of other greenhouse gas levels have increased. Whether this leveling is permanent or just a temporary stay remains unclear.

Computer models and additional research will continue to improve projections of greenhouse gas emissions. But Khalil has come to accept an “irreducible uncertainty” in that science.

“More work in the field is not going to solve these problems,” Khalil says. Taking action to combat global warming will mean moving forward with policies and investments—without definitive answers or guaranteed results. That remains a major stumbling block to advancing climate policies, says Khalil.

For Aslam Khalil, an important piece of the solution is engaging scientists from across disciplines. It also means expanding curriculum to capture growing interest from students.

His undergraduate course, “The Earth’s Atmosphere: Global Change and Human Life” (Physics 375), is open to non-majors and one of only a handful in the nation to explore the systems that intertwine climate change and human (anthropogenic) activities. He is also developing a textbook addressing the topic.

Khalil was lead author of the Oregon Climate Assessment Report’s chapter on “Climate change in Oregon: Defining the problem and its causes.” Commissioned by the Oregon State Legislature and published in December 2010, the document is the first comprehensive assessment of climate issues facing Oregon.

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