Understanding Global Warming

Tornadoes form one after another above the Los Angeles skyline. Flood waters engulf the streets of New York. Sub-zero temperatures cause a massive freeze of the northern United States. These calamities result from a fictional shift in global oceanic circulation patterns, inspired by the very real trend of global warming and illustrated Hollywood-style in director Roland Emmerich’s film “The Day After Tomorrow.”

The 2004 film’s success at the box office left audiences wondering if such a drastic climate change and its apocalyptic aftermath could actually happen. Catastrophic hurricanes, along with unusually warm winters throughout the southeastern United States, have only added to concerns about the effect of global warming on our planet.

Global warming is part of what is known as the greenhouse effect, or the increase in temperature due to the presence of greenhouse gases—such as carbon dioxide and methane—that prevent heat from escaping the Earth’s atmosphere. Although most people think of the greenhouse effect as a dangerous contributor to global warming, UAB civil and environmental engineer Jason Kirby, Ph.D., points out that “the greenhouse effect is also a necessity. If it weren’t for greenhouse gases, we would all be frozen.”

Temperature in- creases caused by greenhouse gases can trigger worrisome changes in climate—but these changes are not the same as changes in weather, Kirby points out. To explain the difference, he quotes writer Robert A. Heinlein: “Climate is what you expect, and weather is what you get.” Climate change, he says, “is a statistical variation in the average state of the climate over an extended time period—decades or longer. When a storm blows through, that’s weather.”

Kirby, who works on climate change and its impact on water availability, thinks that “global warming” is an overused phrase. He does agree with the majority of the scientific community who say that the Earth is warming up and has been since the Industrial Revolution. In the 20th century, the United States experienced a 0.6-degree Celsius temperature increase and a 5 to 10 percent change in precipitation, based on national averages.

“Climatic change has the potential to exert significant influence on the economy and human society as a whole,” he says. “Global climatic change may affect established hydrologic cycles, natural ecosystems, water management infrastructure, and the nature of water supply and demand.”

In other words, Kirby believes that global warming’s effect on climate is cause for concern. But as for Emmerich’s film, he says such dramatic changes in climate over three days are not possible. “The worst-case scenario would be a dramatic spatial or temporal shift in regional temperature and precipitation patterns,” he says. “For instance, Birmingham may become the new Seattle, but even this phenomenon would take decades to materialize. Temperatures are going up; precipitation patterns are changing. But what exactly global warming is going to do, I can’t tell you.”

—Molly Folse