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September 21, 2007 > News > Documentary raises question of global dimming

Documentary raises question of global dimming

By Jocelyn Wright | Thresher Editorial Staff

“Dimming the Sun,” a Nova documentary screened at the Rice Media Center on Wednesday, raised the possibility that global dimming, a phenomenon scientists have observed in the past 30 years, could be keeping the earth cooler, despite increased carbon emissions.

Assistant Professor of Civil and Environmental Engineering Dan Cohan introduced the documentary and stayed for a question-and-answer session with the audience.

Global dimming occurs when less sunlight reaches the earth due to changes in cloud types from air pollution. Clouds form when droplets of water attach themselves to naturally occurring particles in the air. When the air is heavily polluted, though, water droplets form around the air pollution particles instead.

Air pollutants have many more edges to which water droplets can attach themselves, resulting in a greater number of small water droplets that make up each cloud. The high quantity of water droplets diffuses the light and reflects more of the sun’s energy, which keeps the earth cooler. Some scientists now suspect that the combination of global warming and global dimming keeps the earth cooler and masks global warming’s full effects.

As countries take more steps to reduce air pollution, we might see a spike in global temperatures as global dimming lessens and we feel the full effects of global warming.

In the question-and-answer session following the documentary, students asked Cohan about potential solutions to global warming. He explained that scientists from around the world have devised a series of partial solutions, called wedges, which, when combined, could reduce greenhouse gas emissions enough to keep the climate from warming to crisis-causing levels. Although implementing each of the wedges is difficult, it is doable, Cohan said.

“Stopping global warming is conceivable but it’s not something that’s going to happen on its own,” Cohan said. “One of the biggest unknowns is what these changes will cause.”

Students generally reacted positively to the documentary.

“I think it brings up really good points,” Sid Richardson College freshman Yilong Yao said. “It makes global warming seem more like something that we might have underestimated and makes it more important [that we] do more to counteract it.”

“I guess I’ve always been concerned about global warming so it’s scary to think that as we think about cleaning up the air we can make the forecast worse for ourselves,” graduate student Katherine Horn said.

The documentary inspired students to take steps to address global warming.

“I had vaguely heard about [global dimming] but I thought [the documentary] was good because it provided another perspective on global warming,” Baker College senior Karla Gleichauf said. “I’ve always believed that [global warming is] happening but this is just a warning that something needs to be done.”

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